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ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V007T00A001. doi:10.1115/IMECE2018-NS7.
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This online compilation of papers from the ASME 2018 International Mechanical Engineering Congress and Exposition (IMECE2018) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 11th Forum on Fluid Measurements and Instrumentation

2018;():V007T09A001. doi:10.1115/IMECE2018-86963.

Green walls are bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. Green walls can be found indoors or outdoors and they are classified as passive or active systems. Their benefits include temperature reduction, improvement of air quality and reduction of air pollution, oxygen production as well as the social and psychological wellbeing. They can produce changes in the ambient conditions (temperature and humidity) of the air layers around them which create an interesting insulation effect. The effect of passive green wall modules on the air temperature and on humidity is investigated in this work. A closed chamber made of acrylic sheets is used to monitor the temperature and humidity variation caused by a green wall module placed at its center. Temperature and humidity are measured at different locations inside the chamber during operation for different modules with different plant species.

Topics: Temperature
Commentary by Dr. Valentin Fuster
2018;():V007T09A002. doi:10.1115/IMECE2018-87472.

Current CFD models fail to accurately predict boundary layer asymmetry on spin-stabilized projectiles, particularly in the transonic and subsonic flow regimes. Consequently, these models cannot accurately characterize the Magnus moment, a key component in aerodynamic behavior. This work seeks to capture boundary layer thickness asymmetry, an indicator of Magnus effects, around a spinning projectile using Magnetic Resonance Velocimetry (MRV). The MRV technique allows for collection of three-dimensional, non-intrusive, high-resolution velocity field measurements that can be used for comparison to and validation of current computational models. In this experiment, a modified M80 projectile was designed to thicken the hydrodynamic boundary layer for technique validation. The scaled projectile was mounted in a custom-designed test rig at a 2° nosedown angle of attack. The apparatus rotated the projectile at various spin rates in a constant flow of copper-sulfate solution. Initial results revealed azimuthal differences in boundary layer thickness for three different cases — no spin, nominal spin, and double spin — particularly in the tapered rear (boattail) region of the projectile. The introduction of spin shifted the boundary layer thickness in the spin direction resulting in lateral boundary layer asymmetry in the boattail region, a phenomenon that likely affects the stability of spin-stabilized projectiles.

Commentary by Dr. Valentin Fuster
2018;():V007T09A003. doi:10.1115/IMECE2018-87948.

Weep hole flow rates due to interlayer gap flow generated by an external pressure source are measured experimentally for an AO Smith Layered Pressure Vessel (LPV) at the NASA Marshall Space Flight Center. A Computational Fluid Dynamics (CFD) model of the flow through the interlayer gaps is also done to provide further insight regarding flow behavior. The objectives of this project were: (i), to devise and conduct a suitable experiment that accurately measures weep hole flow rates based on pressure input at a single weep hole, and (ii), to interpret the data and provide recommendations regarding the management of potential leaks or failures of these LPVs. CFD predictions and experimental results both indicated that weep hole flow rates increase with increasing numbers of available layer gaps and increasing pressure. The highest flow rates occurred between weep holes that were longitudinally aligned, with the shortest path between them having no curvature. Flow rate results were not symmetric for weep holes located on opposite sides of any curved path. Results indicate that the proximity of weep holes to longitudinal welds appears to have a significant influence on flow symmetry, and that weep hole flow measurement may be a good indicator of localized gapping and inconsistent layer concentricity.

Commentary by Dr. Valentin Fuster
2018;():V007T09A004. doi:10.1115/IMECE2018-88013.

Stereoscopic particle image velocimetry (SPIV) is a variant of particle image velocimetry (PIV) that allows for the measurement of three components of velocity along a plane in a flow field. In PIV, particles in the flow field are tracked by reflecting laser light from tracer particles into two angled cameras, allowing for the velocity field to be determined. Particle shadow velocimetry (PSV) is an inherently less expensive velocity measurement method since the method images shadows cast by particles from an LED backlight instead of scattered light from a laser. Previous studies have shown that PSV is an adequate substitute for PIV for many two-dimensional, two-component velocimetry measurements. In this work, the viability of the two-dimensional, three-component stereoscopic particle shadow velocimetry (SPSV) is demonstrated by using SPSV to examine a simple jet flow. Results obtained using SPIV are also used to provide benchmark comparison for SPSV measurements. Results show that in-plane and out-of-plane velocities measured using SPSV are comparable to those measured using SPIV.

Commentary by Dr. Valentin Fuster
2018;():V007T09A005. doi:10.1115/IMECE2018-88555.

Recent studies have shown that adding polymeric additives to hydrocarbon-based fuels can lead to suppression of their splashing behavior, as well as enhance their burning rates. However, there is a lack of objective data on polymeric additives settling times in these fuels. Choosing Dodecane as a representative of diesel-based fuels, present research experimentally investigates the settling behavior of polymeric additives (graphene) when mixed in with Dodecane, and the effects of various surfactants on such behavior. Methodology for experimental setup, data collection and data analysis is presented. Various concentrations of additives and surfactants are analyzed, and trends for settling times are shown.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 14th Forum on Recent Developments in Multiphase Flow

2018;():V007T09A006. doi:10.1115/IMECE2018-86330.

Large eddy simulation (LES) is conducted to characterize oxygen dissolution in the draft tube of a pre-designed and optimized modular pump-turbine system. The air injection is applied over the peripheral surface on the draft tube. Mixture multiphase model is used to predict the spatial and temporal distribution of the air and the water. The simulation is conducted at the best efficiency point with a Reynolds number of 1.06 × 107 which is based on the rotation speed and the reference diameter of the runner. The vorticity is suppressed inside the draft tube, and the standard deviation of the power generation is decreased roughly 70% after aeration. The power generation is reduced by approximately 4–5% with peripheral aeration. Almost uniform dissolved oxygen concentration of 2–3 mg/l is observed in the radial direction near the outlet which is more than sufficient for wastewater treatment process.

Commentary by Dr. Valentin Fuster
2018;():V007T09A007. doi:10.1115/IMECE2018-86710.

Vacuum and low pressures are needed in many applications, and the liquid-ring vacuum pump, which does not have any solid-solid contacts between moving and stationary parts, is widely used because of its low operational cost and long service life. Though progress has been made in advancing this pump, industry still has aggressive goals on improving its efficiency and performance.

In this study, a reduced-order model was developed to predict the ability of liquid-ring pumps to ingest air and thereby create lower pressure as a function of pump design and operating parameters. The model developed is semi-empirical — constructed by first analyzing available experimental data to extract features and trends and then encapsulating them into a model through appropriate dimensionless parameters. This model by being in closed form shows the functional relationship between the pump’s design and operating parameters and its ability to ingest air and create a vacuum. To make predictions, this model only requires the following inputs: suction pressure, impeller’s rotational speed, and a few dimensions of the pump.

The model developed was assessed by using it to predict the ability of the pump to ingest air for a wide range of suction pressures (cavitation pressure to 760 torr), rotor speeds (up to 1,750 rpm), and dimensions of the pump (radius and span of the impeller blade, hub radius) and then comparing predictions with experimental data not used in the creation of the model. The model developed was found to be accurate within 11% of the experimental data.

Topics: Vacuum pumps
Commentary by Dr. Valentin Fuster
2018;():V007T09A008. doi:10.1115/IMECE2018-87108.

In this article, two-phase slug regime in a duct with rectangular cross-section is investigated numerically, using the volume of fluid (VOF) method. Equations of mass, momentum and advection of volume fraction are solved accompanying k-∈ realizable turbulence equations. To ensure the creditability, numerical results have been compared with experimental results using same geometry. With occurrence of instability in the entrance of duct, Kelvin-Helmholtz condition satisfies and with increasing instability, slug phenomenon occurs. With closing the cross-section of duct, slug causes pressure gradient in it. Trapped air behind a slug transfers the momentum and increases the kinetic energy of slug. In this research the kinetic energy of a slug is investigated.

Commentary by Dr. Valentin Fuster
2018;():V007T09A009. doi:10.1115/IMECE2018-87118.

In this research, the two-phase slug regime is investigated analytically with an engineering approach. due to the velocity gradient in the layers of the two-phase flow, numbers of waves form and grow in the liquid phase and may block the duct which in this case is called slug. Blocking the flow, it causes higher pressure accumulation which is the main reason of slug’s momentum through the duct. Simplifying the slug’s geometry and using basic physics laws yielded an equation between the slug’s back pressure and its length.

Commentary by Dr. Valentin Fuster
2018;():V007T09A010. doi:10.1115/IMECE2018-87136.

Unlike the conventional lattice Boltzmann method (LBM), the discrete Boltzmann method (DBM) is Eulerian in nature and decouples the discretization of particle velocity space from configuration space and time space, which allows the use of an unstructured grid to exactly capture complex boundary geometries. A discrete Boltzmann model that solves the discrete Boltzmann equation (DBE) with the finite volume method (FVM) on a triangular unstructured grid is developed. The accuracy of the model is improved with the proposed high-order flux schemes and interpolation scheme. The boundary treatment for commonly used boundary conditions is also formulated. A series of problems with both periodic and non-periodic boundaries are simulated. The results show that the new model can significantly reduce numerical viscosity.

Commentary by Dr. Valentin Fuster
2018;():V007T09A011. doi:10.1115/IMECE2018-87513.

Multiphase flows are encountered in many engineering problems. Particularly in the oil and gas industry, many applications involve the transportation of a mixture of oil and natural gas in long pipelines from offshore platforms to the continent. Numerical simulations of steady and unsteady flows in pipelines are usually based on one-dimensional models, such as the two-fluid model, the drift-flux model and the homogeneous equilibrium model. The 1991’s version of the well-known and widely-used commercial software OLGA describes a system of non-linear equations of the two-fluid-model type, with an extra equation for the presence of liquid droplets. It is well known that one-dimensional formulations may be physically inconsistent due to the loss of hyperbolicity. In these cases, the associated eigenvalues become complex numbers and the model loses physical meaning locally. This paper presents a numerical study of the 1991’s version of the software OLGA, for an isothermal flow of stratified pattern, in a horizontal pipeline. For each point of interest in the stratified-pattern flow map, the eigenvalues are numerically calculated in order to verify if the eigenvalues are real and also to assess their signs. The results indicate that the model is conditionally hyperbolic and loses hyperbolicity in a vast area of the stratified region under certain flow conditions. Even though the model is not unconditionally hyperbolic, some simulations here performed for typical offshore pipeline flows are shown to be in the hyperbolic region.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
2018;():V007T09A012. doi:10.1115/IMECE2018-87571.

Numerical simulation is a very useful tool for the prediction of physical quantities in two-phase flows. One important application is the study of oil-gas flows in pipelines, which is necessary for the proper selection of the equipment connected to the line during the pipeline design stage and also during the pipeline operation stage. The understanding of the phenomena present in this type of flow is more crucial under the occurrence of undesired effects in the duct, such as hydrate formation, fluid leakage, PIG passage, and valve shutdown. An efficient manner to model two-phase flows in long pipelines regarding a compromise between numerical accuracy and cost is the use of a one-dimensional two-fluid model, discretized with an appropriate numerical method. A two-fluid model consists of a system of non-linear partial differential equations that represent the mass, momentum and energy conservation principles, written for each phase. Depending on the two-fluid model employed, the system of equations may lose hyperbolicity and render the initial-boundary-value problem illposed. This paper uses an unconditionally hyperbolic two-fluid model for solving two-phase flows in pipelines in order to guarantee that the solution presents physical consistency. The mathematical model here referred to as the 5E2P (five equations and two pressures) comprises two equations of continuity and two momentum conservation equations, one for each phase, and one equation for the transport of the volume fraction. A priori this model considers two distinct pressures, one for each phase, and correlates them through a pressure relaxation procedure. This paper presents simulation cases for stratified two-phase flows in horizontal pipelines solved with the 5E2P coupled with the flux corrected transport method. The objective is to evaluate the numerical model capacity to adequately describe the velocities, pressures and volume fraction distributions along the duct.

Commentary by Dr. Valentin Fuster
2018;():V007T09A013. doi:10.1115/IMECE2018-87652.

Experimental study of air bubble formation from orifice plates submerged in water pools has been carried out. Air is forced through the orifice by supplying it to a chamber connected to the orifice plate. The chamber volume plays an important role in determining the bubble growth time as well as bubble size and shape at departure. The effect of chamber volume is generally correlated in term of a dimensionless parameter, capacitance number (Nc), which is proportional to the chamber volume and is inversely proportional to the square of the orifice diameter. To better understand and characterize this effect, an experimental study is performed using ten orifice plates of diameter ranging from 0.61 mm to 2.261 mm with six different chamber volumes between 12 cc and 59 cc with the corresponding capacitance numbers varying from 0.2 to 19. The shape and size of the bubble are captured using high speed videography. The orifice plate material is acrylic glass which has an equilibrium contact angle of 38° with pure water. It was observed that the value of critical capacitance number or Nc above which the bubble evolution is affected by the gas chamber volume, is around 0.85. The bubbles are more spherical in shape, and the growth time is significantly smaller. Also, at high capacitance number (Nc > 7), the air flow in the bubble is so high that the bubble departs with a sharp apex and has a large volume. Above Nc > 10, the chamber effects plateau and further increase in gas chamber volume does not alter bubble size and shape at departure.

Commentary by Dr. Valentin Fuster
2018;():V007T09A014. doi:10.1115/IMECE2018-88098.

The detailed characterization of a fluid flow following a convergent shock wave impinging a perturbed density interface is an extremely complex task as this flow combines geometry effects, compressibility effects and turbulence. Nonetheless, more understanding is necessary to be able to develop models that help accurately predict the flow behavior when occurring in engineering applications. Such an application is Inertial Confinement Fusion (ICF), where turbulent mixing induced by the interaction of the shock wave with the fuel pellet is detrimental to the fusion process. This interaction triggers mixing due to baroclinic vorticity deposition at the density interface in a phenomenon known as the Richtmyer-Meshkov Instability (RM). Next, the Rayleigh-Taylor Instability (RT) is driving the final growth of the mixing layer limited by secondary instabilities such as the Kelvin-Helmholtz Instability (KH). These classical hydrodynamic instabilities (HI) trigger the mixing process that leads ultimately to a highly-mixed fluid layer. For this study, we simulate a cylindrical Sulfur hexafluoride (SF6) target immersed into an air medium. The incident shock wave is regarded as a Chisnell-type converging shock wave impinging into a perturbed cylindrical density discontinuity generated with a wave-like spatial perturbation spectra. Parameters of interest are the growth rate and width of the mixing layer at the density discontinuity. This study aims at describing and quantifying relevant aspects of these flows coupling mixing layer growth with perturbation modes.

Topics: Density , Shock waves
Commentary by Dr. Valentin Fuster
2018;():V007T09A015. doi:10.1115/IMECE2018-88438.

Phase separation has been proven to be beneficial to air-cooled parallel flow microchannel condensers for air conditioning systems. The inlet to the condenser with phase separation is located at the middle of the condenser height. After the first pass, in the vertical second header of the condenser, vapor phase separates from liquid phase mainly due to gravitational effects. In ideal case vapor should go to the top exit and liquid to the bottom exit, resulting in increased heat transfer. Due to interaction between vapor and liquid, separation is not perfect, expressed through the separation efficiency.

This paper presents a parametric study of phase separation efficiency in the intermediate headers, with the target to improve separation efficiency. Header prototypes which have two exits are made with transparent PVC to simulate the real header and provide visual access. Using R-134a as a baseline, the measurement of separation efficiency and its general trend will be shown first. The results are compared to those of a mechanistic model based on flow regime and force balance analysis. Inlet mass flux in simulation is controlled at 87 kg·m−2·s−1 – 311 kg·m−2·s−1 and inlet quality at 0.05–0.25. The observed flow patterns in header are compared with the modeling results as well. Then, the header diameter is increased, which effectively improves the separation efficiency due to reduction of vapor velocity in header. Finally, R245fa and R32 are modeled in comparison with R-134a to discuss the effect of fluid properties on separation efficiency.

Commentary by Dr. Valentin Fuster
2018;():V007T09A016. doi:10.1115/IMECE2018-88481.

Over the past 2 decades, GLCC© compact separators have been replacing the conventional vessel type separators in the Oil & Gas Industry, because of its numerous advantages. Despite these advantages, GLCC separators face two critical problems affecting the performance under extreme operating conditions, namely, Liquid Carry Over (LCO) into the gas leg and Gas Carry Under (GCU) into the liquid leg. This study focuses on the LCO phenomenon. Having a deeper insight into the LCO flow phenomenon helps us to enhance the technical performance of GLCC at these extreme conditions. Several studies were presented in the past on experimental investigations and mechanistic modeling of LCO. In the above cases, mechanistic modeling of LCO was based on Zero Net liquid Holdup (ZNLH) parameter. The liquid holdup in the upper part of the GLCC before it is blown out by gas flow is referred to as ZNLH. ZNLH is an important phenomenon affecting the GLCC pressure behavior and performance characteristics. Above mentioned experimental investigations performed to calculate ZNLH were carried out under static conditions where the effects of superficial liquid velocities were neglected. Investigations have been carried out in this study under dynamic conditions to evaluate the effect of superficial liquid velocities on ZNLH. We found that Dynamic ZNLH results are different from static ZNLH data as they show lower liquid holdup for the same gas velocities. A mechanistic model is proposed in this study to predict dynamic ZNLH and this model is validated against the dynamic ZNLH experimental data. It may be noted that a suitable ZNLH model will help in improving the predictions of the LCO mechanistic model considerably.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2018;():V007T09A017. doi:10.1115/IMECE2018-88531.

Periodic mixing using pulse jet mixers is being developed and applied for processing unique slurries of radioactive waste that depending upon the slurry properties may possess either Newtonian or non-Newtonian characteristics. To investigate the performance of these mixing systems, scaled experimental fluid dynamics (EFD) experiments have been conducted and in addition, for certain investigations, computational fluid dynamics (CFD) simulations have been applied. The purpose of this paper is to describe the periodic mixing processes, elaborate regarding the types of scaled experiments that were conducted, and present examples of computational investigations conducted to further define the mixing system performance. The experimental investigations showed the ability to track visual metrics such as cloud height and cavern size. The computational investigations demonstrated the ability to model full-scale experiments with Newtonian slurries.

Commentary by Dr. Valentin Fuster
2018;():V007T09A018. doi:10.1115/IMECE2018-88586.

Sediment erosion is recognized as a serious engineering problem in slurry handling such as screw centrifugal pump, which has wide efficiency region and non-plugging performance. In the present study, the screw centrifugal pump was simulated based on the Euler-Lagrange method. The Mclaury model was adopted for the erosion prediction of flow passage components. By analyzing the correlation factor functions contained in the erosion model and performing some preliminary research with a simplified model, particle velocity, particle shape factor and particle concentration were selected as the influencing factors to analysis the quantitative relationship among particle parameters, erosion wear and performance of screw centrifugal pump. The results show that the erosion of volute casing is higher than impeller, and the erosion rate of suction side is higher than pressure side. The particles velocity is positively correlated with erosion wear and pump performance reduction rate. While the increase of particles shape factor shows the opposite trend. Erosion rate is found to be increases sharply and then slowly when particles concentration increases, because of the adhesion effect of sand particles in the volute casing inhibits the total erosion wear. The increase of erosion rate promoted the reduction rate of pump performance, and the pump efficiency decreased more significantly when the erosion rate increased to a certain extent. The results of this study are of great significance for further optimization of hydraulic design and structural design for screw centrifugal pump.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 16th Symposium on Electric, Magnetic, and Thermal Phenomena in Micro and Nano-Scale Systems

2018;():V007T09A019. doi:10.1115/IMECE2018-86223.

Electrowetting heat pipes (EHPs) are a newly conceptualized class of heat pipes, wherein the adiabatic wick section is replaced by electrowetting-based pumping of the condensate (as droplets) to the evaporator. Specific advantages include the ability to transport high heat loads over long distances, low thermal resistance and power consumption, and the absence of moving mechanical parts. In this work, we describe characterization of key microfluidic operations (droplet motion and splitting) underlying the EHP on the International Space Station (ISS). A rapid manufacturing method was used to fabricate the electrowetting device on a printed circuit board. Key device-related considerations were to ensure reliability and package the experimental hardware within a confined space. Onboard the ISS, experiments were conducted to study electrowetting-based droplet motion and droplet splitting, by imaging droplet manipulation operations via pre-programmed electrical actuation sequences. An applied electric field of 36 Volts/um resulted in droplet speeds approaching 10 mm/s. Droplet splitting dynamics was observed and the time required to split droplets was quantified. Droplet motion data was analyzed to estimate the contact line friction coefficient. Overall, this demonstration is the first-ever electrowetting experiment in space. The obtained results are useful for future design of the EHP and other electrowetting-based systems for microgravity applications. The testing was performed under the Advanced Passive Thermal eXperiment (APTx) project, a project to test a suite of passive thermal control devices funded by the ISS Technology Demonstration Office at NASA JSC.

Commentary by Dr. Valentin Fuster
2018;():V007T09A020. doi:10.1115/IMECE2018-86487.

The influence of an electric field on a water droplet resting at the interface of two immiscible liquids is studied experimentally and theoretically. The droplet is initially in a state of equilibrium due to the balance between gravitational, buoyancy and capillary forces. Application of an electric field across the droplet-interface system disturbs the equilibrium. The electrical force increases the immersion angle of the droplet and eventually causes it to ‘sink’ when a critical immersion angle is reached.

Experiments are conducted with a deionized water droplet, resting at the interface of silicone oil and sunflower oil. Experiments involve the application of an electric field and image analysis to track the voltage dependent immersion angle. The objective is to determine the threshold voltage at which the droplet sinks. Experiments are complemented by an analytical model that balances gravity, buoyancy, capillary, and dielectrophoretic forces to predict the change in the position of the droplet and the immersion angle. Experiments and analysis were conducted for Bond numbers ranging from 0.1 to 1.7, the latter being the critical size at which a droplet will ‘sink’ due to its weight. The predicted immersion angles and threshold voltage show a good match to the experimental measurements. Overall, this work highlights the utility of electric fields to control interfacial phenomena at the interface of two immiscible liquids.

Topics: Drops
Commentary by Dr. Valentin Fuster

Fluids Engineering: 18th International Symposium on Measurement and Modeling of Environmental Flows

2018;():V007T09A021. doi:10.1115/IMECE2018-87697.

Many environmental flows are simulated in a Cartesian domain using buoyancy-driven incompressible Navier-Stokes equations. A significant cost of the simulation is devoted to the solution of the elliptic pressure equation to enforce the conservation of mass principle. The legacy software, FISHPACK, has been used for this purpose for many years. We present a new software package for the direct solution of the pressure Poisson’s equation on a directionally uniform Cartesian mesh with a second-order accurate finite-difference formulation. We use the separation of variables principle and adopt fast Fourier transforms (FFT) to convert the system to a group of independent tridiagonal systems that can be solved directly. The computational complexity of the present methodology is proportional to N2 (O(NlogN)). However, each stage of the solution algorithm can be performed simultaneously leading to a pleasingly parallel problem that is well suited for massively-threaded accelerators, such as modern graphics processing units (GPU). Theoretically speaking, if an accelerator can sustain N2 resident threads, the computational complexity will drop to O(NlogN). We use OpenACC directives with cuFFT library on a GPU to realize substantial acceleration of the overall solution algorithm and compare its performance relative to an implementation that used the FFTW library on central processing units (CPU). For a problem with 5123 points, the GPU version is about 17 × faster than the CPU version.

Commentary by Dr. Valentin Fuster
2018;():V007T09A022. doi:10.1115/IMECE2018-88449.

Miscible displacement flow in a curved pipe with two fluids of equal viscosity and in the regime of low Atwood number is studied experimentally at different Reynolds and Atwood numbers. By using a curved pipe the effect of curvature on miscible displacement flow is studied. Curvature may be present in many displacement flow processes in nature or industry which underlines the necessity of studying its effect on displacement flow. As the flow is controlled by gravity as the main driving force, only low to moderate Reynolds numbers are considered and Atwood number is varied by adding NaCl salt to fresh water. This makes it possible to create different values of Atwood numbers which can be varied continuously. The position of the leading front is carefully recorded using a digital camera and is used as a measure of displacement efficiency. It is observed that the ratio of the front velocity to the mean velocity approaches a certain value as Reynolds number increases. The effect of Atwood number on flow dynamics is also studied based on experimental results and is interpreted following the conventions employed in some of the previous researches.

Commentary by Dr. Valentin Fuster
2018;():V007T09A023. doi:10.1115/IMECE2018-88666.

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment by decreasing moisture content in the air and reducing pollutants concentration. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Generally, it is difficult for wind to change its direction, and enter a room through usual openings, the windcatcher is designed to overcome such problems since they have vertical columns aimed at helping wind to channel down to the inside of a building. The efficiency of a windcatcher is maximized by applying special forms of opening and exit. The openings depend on the windcatcher’s location and on its cross sectional area and shape such as square, rectangular, hexagonal or circular. In this study the effect of different wind speeds on the total air flow captured by different inlet designs is investigated. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a two dimensional room fitted with a windcatcher applying wind speeds from 1 m/s up to 14 m/s and based on different inlet designs such as a uniform inlet, a divergent inlet and a bulging-convergent inlet.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 24th Symposium on Fundamental Issues and Perspectives in Fluid Mechanics

2018;():V007T09A024. doi:10.1115/IMECE2018-86128.

Extracting free energy has long been a goal of science but is mostly considered impossible to achieve. Natural processes having independent movement, such as rivers and wind, are often used but provide varied effectiveness. However, coordinated instability within a statically pressurized ambience can be used to extract a significant percentage of the ambient potential energy. This method creates two pathways between two adjacent points, one being a chaotic or Coriolis swirling path and the other being a direct path, thereby creating a pressure difference between the two adjacent points, which can be harvested to reduce the kinetic energy input required to perform the process.

While some refer to the proposed benefits as “perpetual motion,” it is necessary to understand that 55 to 80% of the required kinetic energy would still be mechanically generated; therefore, they could be better referred to as “coordinated chaos” or a “Coriolis energy extractor” to save energy [1].

This paper studies direct returns—extracting energy directly from a static (not dynamic) ambient energy. While such returns might not be substantial in normal activities, in deepwater or underground applications (e.g., oil or gas wells), they can be significant, often equating to a 20–45% reduction in fuel use or pollutant generation. In operations that use 20,000 horsepower, this could represent a savings of 4,000 horsepower or 10,000,000 Btu/hr with no associated financial costs.

Commentary by Dr. Valentin Fuster
2018;():V007T09A025. doi:10.1115/IMECE2018-86302.

In this work, a central difference finite volume lattice Boltzmann method (CDFV-LBM) is developed to compute 2D inviscid compressible flows on triangular meshes. The numerical solution procedure adopted here for solving the lattice Boltzmann equation is nearly the same as the procedure used by Jameson et al. for the solution of the Euler equations. The integral form of the lattice Boltzmann equation using the Gauss divergence theorem is applied on a triangular cell and the numerical fluxes on each edge of the cell are set to the average of their values at the two adjacent cells. Appropriate numerical dissipation terms are added to the discretized lattice Boltzmann equation to have a stable solution. The Boltzmann equation is discretized in time using the fourth-order Runge-Kutta scheme. The computations are performed for three problems, namely, the isentropic vortex and the supersonic flow around a NACA0012 airfoil and over a circular-arc bump. The effect of changing the grid resolution and the dissipation coefficients on the accuracy of the results is also studied. Results obtained by applying the CDFV-LBM are compared with the available numerical results which show good agreement.

Commentary by Dr. Valentin Fuster
2018;():V007T09A026. doi:10.1115/IMECE2018-86331.

The effect of the inclination angle of a delta winglet vortex generator with a length-to-height (c/h) ratio of 2, at 30 degrees with respect to an Reh = 9000 wind, on the resulting flow along a flat plate is quantified in a wind tunnel. The vortical flow characteristics at 13h downstream of the leading edge of the delta winglet are detailed with the help of a triple-hot-wire probe. Specifically, the local velocity, vortex shape, size and strength, turbulence intensity, integral length and Taylor microscale are deduced. The results show that the into-the-plate velocity in the inflow region increases, while the out-of-the-plate velocity in the outflow area decreases, with inclination angle. The 90-degree inclination angle appears to furnish higher values of turbulent intensity, integral length and Taylor microscale.

Topics: Vortex flow
Commentary by Dr. Valentin Fuster
2018;():V007T09A027. doi:10.1115/IMECE2018-86852.

The formulation of simplified models in the description of flow fields can be highly interesting in many complex network such as the circulatory system. This work presents a refined one-dimensional finite element model with node-dependent kinematics applied to incompressible and laminar flows. In the framework of 1D-FE modelling, this methodology is a new development of the Carrera Unified Formulation (CUF), which is largely employed in structural mechanics. According to the CUF, the weak formulation of the Stokes problem is expressed in terms of fundamental nuclei and, in this novel implementation, the kinematics can be defined node by node, realizing different levels of refinements within the main direction of the pipe. Such feature allows to increase the accuracy of the model only in the areas of the domain where it is required, i.e. particular boundary condition, barriers or sudden expansion. Some typical CFD examples are proposed to validate this novel technique, including Stokes flows in uniform and non-uniform domains. For each numerical example, different combinations of 1D models have been considered to account for different kinematic approximations of flows, and in particular, models based on Taylor and Lagrange expansion have been used. The results, compared with ones obtained from uniform kinematics 1D models and with those come from available tools, highlight the capability of the proposed model in handling non-conventional boundary conditions with ease and in preserving the computational cost without any accuracy loss.

Commentary by Dr. Valentin Fuster
2018;():V007T09A028. doi:10.1115/IMECE2018-86870.

We present a unique method for solving for the Reynolds stress in turbulent canonical flows, based on the momentum balance for a control volume moving at the local mean velocity. A differential transform converts this momentum balance to a closed form, with the longitudinal component, u’2 and the mean velocity, U as its constituents. Validations with experimental and computational data in simple geometries show quite good results. Using this perspective, determination of the Reynolds stress in terms of computable turbulence parameters is rendered possible.

Topics: Turbulence , Stress
Commentary by Dr. Valentin Fuster
2018;():V007T09A029. doi:10.1115/IMECE2018-87178.

This work determines the inaccuracy of using Reynolds averaged Navier Stokes (RANS) turbulence models in transition to turbulent flow regimes by predicting the model-based discrepancies between RANS and large eddy simulation (LES) models. Then, it incorporates the capabilities of machine learning algorithms to characterize the discrepancies which are defined as a function of mean flow properties of RANS simulations. First, three-dimensional CFD simulations using k-omega Shear Stress Transport (SST) and dynamic one-equation subgrid-scale models are conducted in a wall-bounded channel containing a cylinder for RANS and LES, respectively, to identify the turbulent kinetic energy discrepancy. Second, several flow features such as viscosity ratio, wall-distance based Reynolds number, and vortex stretching are calculated from the mean flow properties of RANS. Then the discrepancy is regressed on these flow features using the Random Forests regression algorithm. Finally, the discrepancy of the test flow is predicted using the trained algorithm. The results reveal that a significant discrepancy exists between RANS and LES simulations, and ML algorithm successfully predicts the increased model uncertainties caused by the employment of k-omega SST turbulence model for transitional fluid flows.

Commentary by Dr. Valentin Fuster
2018;():V007T09A030. doi:10.1115/IMECE2018-87212.

Organic Rankine cycle (ORC) has gained an increasing worldwide attention due to its high efficiency in converting low-grade thermal energy into electricity. The expander is the most critical component in the ORC system. Among the influential factors that define the performance of the expander, the velocity coefficient of the nozzle is crucial. This work numerically investigates the effects of the nozzle height, length, surface roughness, outlet geometric angle, and expansion ratio, on the velocity coefficient of the nozzle in the ORC turbine with hexamethyldisiloxane (MM) as working fluid. In the 3-D viscous numerical analysis, the shear stress transports k-ω turbulence model is employed and the numerical method is verified by the experimental data of the nozzle with pressured air based on hotwire technology. The numerical results show that the velocity coefficient is almost independent of expansion ratio compared to other factors due to the relatively small flow boundary layer and high Reynolds number. Since the existing correlations for the gas nozzle cannot well predict the velocity coefficient of the organic nozzle, an empirical equation is proposed according to the numerical results with the maximum deviation of 3.0%.

Topics: Fluids , Nozzles , Turbines
Commentary by Dr. Valentin Fuster
2018;():V007T09A031. doi:10.1115/IMECE2018-87846.

With the increasing prevalence of additive manufacturing, geometries that would not have been possible to manufacture just a few years ago are becoming a reality. One example is the ability to create pipes with integral, geometry compliant lattice structures. These compliant lattice structures offer the potential to greatly enhance heat transfer in arbitrary flow passages. This preliminary paper will focus on the development of an isothermal simulation model in OpenFOAM, to model the nature of the flow for a single unit cell, a unit cell screen, and a series of unit cell screens.

Honeywell FM&T is a contractor of the U.S. Government under Contract No. DE-NA0002839.

Commentary by Dr. Valentin Fuster
2018;():V007T09A032. doi:10.1115/IMECE2018-88187.

A variety of engineering applications involve medium Reynolds number (Re) oscillating flow around spherical objects (e.g. aerosol dispersion, microorganism motion, sedimentation of small particles, etc.), and they usually require accurate prediction of the movement of particles and the forces. Currently, the popular model of predicting forces acting on an accelerated submerged sphere was developed more than 100 years ago, but only limited to Stokes flow (Re << 1). In the 1960s, Odar and Hamilton conducted experiments and extended the model for Re number up to 64 (OH-64 law). The aim of this study is to further extend the Re number to 300 via numerical simulations using ANSYS Fluent, so that the model is more capable for more varieties of engineering applications. It is expected that the results of this study will be beneficial to advance the fundamental understanding of oscillating flow over spheres and the potential applications.

Commentary by Dr. Valentin Fuster
2018;():V007T09A033. doi:10.1115/IMECE2018-88238.

Journal bearings of high torque diesel engines are used to cater for high combustion loads which are applied intermittently. A lubrication layer is provided between journal (crankshaft) and bearing to avoid contact between them. The relative velocity between crankshaft and journal bearing results in viscous shear heating among the different layers of lubricating oil. The shear heating reduces the viscosity of the lubricant that ultimately reduces the load carrying ability of the journal bearing. It offers a physical contact and reduces the designed life of crankshaft. In this study the 2-D transient numerical lubrication model is developed by employing the Reynolds equation to calculate the pressure and film thickness profiles as a function of crankshaft speed. The shear heating effects are determined by coupling the energy equation with lubrication model. The finite difference method is used and an appropriate numerical scheme is employed to simulate the conduction and convection based thermal energy transfer in transient and steady state journal bearing lubrication model. The lateral displacement of crankshaft is incorporated in the thermal model to analyze the effect of secondary dynamics of crankshaft. The viscosity and temperature relationship are used to ascertain its variation with temperature. The characteristic of three different viscosity-grade lubricates are incorporated separately in the model to carry out the comprehensive comparative analysis. The results are simulated for particular application where low operating speed and length to width ratio of journal bearing is fixed and analyzed the results for complete 720 degrees of crankshaft in its two revolutions. The results show that the oil with high viscosity produces high hydrodynamic pressures as compared to the oil that have low viscosity. The viscous shearing temperature reduces the hydrodynamic pressures but still the high viscosity lubricating oil have enough pressures to uplift the shaft after incorporating the shear heating effects. This study determines the hydrodynamic pressure, and variation of density, viscosity and thermal-conductivity with temperature for three different lubricating oils. These analyses will facilities towards the selection of appropriate lubricant for high torque low speed diesel engine in order to enhance the life of crankshaft.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 25th Symposium on Fluid Mechanics and Rheology of Nonlinear Materials and Complex Fluids

2018;():V007T09A034. doi:10.1115/IMECE2018-86044.

Surfactant-based fluids, SB fluids exhibit complex rheological behavior due to substantial structural change caused by the molecules self-assembled colloidal aggregation. Various factors affect their rheological properties. Among these factors, surfactant concentration, shear rate, temperature, and salinity are investigated. One of the most popular surfactants, Aromox® APA-T viscoelastic surfactant (VES) is examined. The study focuses on four different concentrations (1.5%, 2%, 3%, and 4%) over a shear rate ranging from 0.0526 sec−1 to 1944 sec−1 using Bohlin rheometer. For salinity effects, two brine solutions are used; 2 and 4% KCl while for temperature effects, a wide range from ambient temperature of 72°F up to 200°F is covered. The results show that SB fluids exhibit a complex rheological behavior due to its unique nature and the various structures form in the solution. In general, SB fluids at all concentrations exhibit a non-Newtonian pseudo-plastic shear thinning behavior. As the surfactant concentration and/or shear increases, a stronger shear thinning behavior can be seen. Increasing solution salinity promotes formation of rod-like micelles and increases its flexibility. Salinity affects micelles’ growth and their rheological behavior is very sensitive to the nature and structure of the added salt. Different molecular structures are formed; spherical micelles occur first and then increased shear rate and/or salinity promotes the formation of rod-like micelles. Later, rod-like micelles are aligned in the flow direction and form a large super ordered structure of micellar bundles or aggregates called shear induced structure (SIS). Different structures implies different rheological properties. Likewise, rheology improves with increasing temperature up to 100°F. Further increase in temperature reverses the effects and viscosity decreases. However, the effects of temperature and salinity diminish at higher shear rates. Furthermore, a rheology master curve is developed to further understand the rheological behavior of SB fluids and correlate rheological properties to its microscopic structure.

Commentary by Dr. Valentin Fuster
2018;():V007T09A035. doi:10.1115/IMECE2018-86112.

Flow patterns in molten quartz are highly related to the bubble transport and removal. Understanding the flow behavior in molten quartz is of great importance to the manufacture of high-purity quartz glass. In this paper, a numerical model is set up to simulate the flow field of molten quartz in a typical electric heating furnace. Natural convection and Marangoni convection are examined for their respective effects on the flow pattern of molten quartz. Different heater arrangements will change the flow field by varying temperature distributions. Top heating and bottom heating have the same vortex direction; while side heating induces an opposite direction to them. To improve the flow field in molten quartz, forced convection is introduced by crucible rotation. The influences of rotating speed of crucible on the flow field are studied in a wide range varying from 0 to 100 rad/s. With the increase of rotating speed, a reverse vortex to natural convection shows in molten quartz; and the velocity magnitude increase at a growing speed. To find out the optimal flow pattern for quartz glass manufacture, a qualitative analysis is presented on the reliance of bubble transport behavior on the convection modes. Based on the results, useful suggestions are provided towards increasing the bubble-free area of molten quartz and improving the quality of quartz glass.

Commentary by Dr. Valentin Fuster
2018;():V007T09A036. doi:10.1115/IMECE2018-86328.

Computational fluid dynamics (CFD) simulations are conducted to study the transport phenomena in spiral wound membranes (SWM) within a Forward Osmosis (FO) module. The effect of the porous layer on the membrane performance is examined. Simulations are prepared for three different porous layer thicknesses by having the porous layer facing the draw channel, a mode known as AL-FS (active layer facing feed solution). In the current study, a Reynolds number range from 2 to 500 is considered. The Navier-Stokes and the mass transport equations are used to obtain the velocity, pressure and concentration fields in the flow channels. The local osmotic pressure and the membrane properties are used to calculate the water permeation over the membrane surface. The membrane is considered as a semipermeable functional surface of zero thickness. The effect of the porous layer is included in the flux model, but the flow and concentration fields in the porous layer are not resolved. The results suggest that increasing the streamwise velocity decreases the level of the external concentration polarization on both sides of the membrane which in turn leads to higher water flux through the membrane. Also, the existence of the porous layer reduced the membrane performance. The water flux didn’t improve much with increasing streamwise velocity at the same porous layer thickness. The suction velocity over the membrane starts at a high value at the inlet of the draw channel and decreases until reaching the outlet of the draw channel then it starts to increase slightly from the effect of the inlet of feed solution. Moreover, by increasing the net osmotic pressure difference, the water flux exhibited a non-linear increase.

Commentary by Dr. Valentin Fuster
2018;():V007T09A037. doi:10.1115/IMECE2018-86544.

The present study addresses physical phenomena of a suspension composed of magnetic spherical particles in an alternating magnetic field in order to elucidate particle aggregation phenomena and their influence on heat production. For this objective, we have performed Brownian dynamics simulations in a variety of circumstances of the magnetic field strength and frequency of an alternating magnetic field, and the magnetic dipole-dipole interaction strength. As in a time-independent uniform external magnetic field, large aggregates are formed in the case of strong magnetic particle-particle interactions. However, these clusters exhibit completely different behaviors that are dependent on the frequency of an alternating magnetic field. If the frequency is significantly high, then the viscous torque is the dominant factor, so that the formation of the clusters is not significantly influenced by the time-dependent magnetic field. If the frequency is significantly low, the magnetic field have a significant effect on the rotational motion of the particles, so that the formation of the cluster is dependent on which factor dominates the particle motion between the applied magnetic field and the magnetic particle-particle interaction. If the magnetic interaction is more dominant than the external field, stable chain-like clusters are formed in the field direction, and the magnetic particle-particle interaction induces a significant delay for the moments inclining in the alternating magnetic field direction. This behavior gives rise to a hysteresis loop with a larger area and therefore a large heating effect is obtained.

Commentary by Dr. Valentin Fuster
2018;():V007T09A038. doi:10.1115/IMECE2018-87092.

This study is focused on the flow of the shear thinning and shear thickening fluids of Herschel-Bulkley type past a partial vertical wall in between the plates. Upon numerically solving the continuity and momentum equations the flow is analyzed throughout the domain using a finite volume scheme. The shear stress at the wall together with velocity distribution are evaluated and compared to experimental results for several values of Herschel-Bulkley coefficients for fluidity and flow behavior index. Dynamic viscosity and other flow variables are calculated throughout the flow domain.

Commentary by Dr. Valentin Fuster
2018;():V007T09A039. doi:10.1115/IMECE2018-87105.

In the present research, the flow of visco-plastic fluid is investigated in a duct with triangular obstacles on the bottom plate. The effect of different inlet velocities on the flow behavior is observed specially around the obstacles. The viscosity as the function of velocity gradient and hence the Reynolds numbers, are obtained on certain lines for different values of fluid characteristics and flow indexes. Herschel-Bulkley model as a generalized model of visco-plastic fluids is used to simulate the fluid motion along the channel. Reverse flows and vortexes are shown before and past the obstacles.

Commentary by Dr. Valentin Fuster
2018;():V007T09A040. doi:10.1115/IMECE2018-87301.

Subsea separation is an attractive and economic solution to develop deep offshore oil and gas fields producing fluid without hydrate or wax. The subsea separation system should be reliable to ensure successful operation in a wide range of multiphase flow regime. A subsea separator can avoid or simplifying costly surface platforms of floating vessels, as well as being an efficient tool to enhance hydrocarbon production. One solution of interest is the separation and re-injection of water at the seabed to avoid bringing the water up to the surface facility. In this study, liquid-liquid flow characteristics inside in-line type subsea separation system are investigated for the design of subsea separation system. The separation efficiency of the subsea separator is determined through experiments that are the liquid-liquid phased separation. Also internal swirl element (ISE) modeling of the separator was optimized. The analysis results were utilized to improve the reliability and efficiency of the subsea separation system.

Commentary by Dr. Valentin Fuster
2018;():V007T09A041. doi:10.1115/IMECE2018-87549.

A comprehensive model of the selective laser sintering (SLS) process at the scale of the part is presented for application to polymeric powders. The powder bed is considered as a continuous medium with homogenized properties. A thermal model with detailed multiphysics coupling is presented. The model accounts for all elements of the thermal history : laser absorption, melting, coalescence, densification and volume shrinkage. For numerical resolution, a 3D in-house fortran code using FV method is developed. The proposed model is validated through the comparison of modeling data with experimental results available in the published literature. A parametric analysis about the thermal efficiency of the heating process against the laser energy input is proposed and the influence on the densification and thermal kinetics is discussed with regarding the evolution of the structure of the material.

Commentary by Dr. Valentin Fuster
2018;():V007T09A042. doi:10.1115/IMECE2018-87568.

Non-isothermal laminar flow of a viscoelastic fluid through a square cross-section duct is analyzed. Viscoelastic stresses are described by the Phan-Thien – Tanner model and the solvent shear stress is given by the linear Newtonian constitutive relationship. The solution of the set of governing equations spawns coupling between equations of elliptic-hyperbolic type. Our numerical approach is based on the finite-differences method. To treat the hyperbolic part, the system of equations are rewritten in a quasilinear form. The resulting pure advection terms are discretized using high-order upwind schemes when the hyper bolicity condition is satisfied. The incompressibility condition is obtained by the semi-implicit projection method. Finally we investigate the evolution of velocity, shear stress, viscosity and heat transfer over a wide range of Weissenberg numbers.

Commentary by Dr. Valentin Fuster
2018;():V007T09A043. doi:10.1115/IMECE2018-87973.

The relaxation response of viscoelastic fluids associated with the natural frequencies of oscillation that arise as a consequence of the structure of the constitutive equation is explored for the case of pulsating flow. The matching of the forcing frequency to the fluid’s natural frequencies induces a multiple resonance phenomenon.

In this paper, the resonance phenomenon is investigated in pulsating flow in straight circular tubes when the fluid is characterized by the Johnson-Segalman constitutive model. An analytical solution is developed based on an asymptotic expansion in terms of a material parameter. The analysis reveals that the forcing frequency associated with the pressure gradient can generate a sequence of resonances of decaying intensity dependent on the material parameter and other fluid constitutive constants. The effects of resonance on the rate of flow and oscillating velocity field are explored for several values of the relevant parameters.

Commentary by Dr. Valentin Fuster
2018;():V007T09A044. doi:10.1115/IMECE2018-88030.

Mixing in laminar flow regimes is crucial for many engineering applications in which highly viscous and fragile fluids are used. Moreover, the compactness of laminar mixers is a great challenge due to the large mixing time required to obtain the desired homogeneity. The “Split And Recombine” (SAR) static mixers are a promising solution for this challenge. This type of mixers consists of a network of separated and then recombined channels in which two fluids are introduced separately and mixed by a multi-lamination process. The SAR static mixers perform a series of baker’s transforms on the concentration profile enhancing thus the mixing process at very low Reynolds numbers. In the present study, numerical simulations are carried out to analyze the mixing process in a new topology of SAR mixer with double separation and recombination in order to increase the lateral gradients and destroy the concentration profile faster. The new geometry proposed here is compared to two SAR configurations widely studied in the open literature namely the Gray and the Chen SAR configurations. The results show a good enhancement of the mixing process in the new double SAR configuration with decrease in the power dissipation.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 27th Symposium on Industrial Flows

2018;():V007T09A045. doi:10.1115/IMECE2018-86018.

Oxygen content in air is approximately 21% by volume. With many industrial uses, mainly in the manufacture of steel and chemicals, for metal cutting, welding ,hardening & scarfing, it is being transported as a non-liquefied gas at pressures of 138 bar (13800000 Pa) or above, also as a cryogenic fluid at pressures and temperatures below 13.8bar (1380000 Pa) & −146.5°C (126.65K). Commonly we found air separation plants produce ultra-pure oxygen (> 99.9% purity) via liquefaction of atmospheric air and separation of the oxygen by fractionation and thereby transported to the needy areas via pipelines.

The research efforts directed towards technical assessment to establish the correlations between valve construction and turbulence and solving the complications in the transported ultra-pure oxygen gas in the pipelines and through mounted valves. Hence, it is necessary to study the performance, complexities and fire hazards associated with the valves transporting it and the preventive measures to avoid any catastrophic failure in ultra-pure gaseous oxygen services. The study was conducted on two isolation valves — each of ball and globe of relative size. It was realized that velocities of the ultrapure gaseous oxygen on the impingement sites inside the valve are beyond the safe limit as recommended by European Industrial Gas Association (EIGA) [4] and various other prominent industrial gas manufacturers. Moreover, globe valve gave relatively less turbulence and velocity at initial opening of the valve. The study revealed that majority of health hazards & accidents on industrial usage of ultra-pure gaseous oxygen media are the result of the inadequate awareness of the degreasing or cleaning and optimum material selection and construction of the valve and fittings on the industrial pipeline.

Topics: Valves , Oxygen , Hazards
Commentary by Dr. Valentin Fuster
2018;():V007T09A046. doi:10.1115/IMECE2018-86327.

This study investigates the effect of membrane properties — porosity, membrane thickness, and pore radius — on the performance of vacuum membrane distillation (VMD) process by achieving computational fluid dynamics (CFD) simulations on a three-dimensional domain of interest at fixed flow properties. The finite volume method (FVM) is adopted to solve momentum, solute mass transport, and energy equations in the feed channel. To accurately predict the rate of water vapor diffused through the membrane by Knudsen and viscous diffusion mechanism, local concentration, temperature, and flux are coupled at the membrane surfaces. In accordance with the flux, corresponding gradients for temperature and concentration are applied at the membrane boundaries. Since there is a strong coupling of flow properties at the membrane surface, the employed model is validated against an experimental study and further used to characterize the effect of PTFE membrane properties on permeate flux, temperature polarization, and concentration polarization. We found that different set of membrane design parameters substantially changes the total mass flux. The contribution of both viscous and Knudsen mechanism is comparable and, as such, prevents us neglecting neither of them. The temperature and concentration polarization are even more undesirable level for the larger pore sizes.

Topics: Vacuum , Membranes
Commentary by Dr. Valentin Fuster
2018;():V007T09A047. doi:10.1115/IMECE2018-86333.

Computational fluid dynamics simulations were performed on Francis turbine using Reynolds-averaged Navier-Stokes (RANS) with k-ω SST turbulence model. Simulations were conducted at the turbine’s best efficiency point with a Reynolds number of 2.01 × 107. Water injection was admitted from the runner cone in the stream-wise direction. The aim of this process was to investigate the influence of water injection on the turbine performance and the pressure pulsation. The water injection did not affect the nominal value of the turbine’s power generation. Straight vortex rope was observed at the centerline of the draft tube. Moreover, helix-shaped vortex ropes were obtained near the draft tube surface. The water injection expands the central vortex rope, but it did not suppress or disrupt the helix-shaped peripheral vortex rope near the draft tube surface. The pressure fluctuation became less regular after the water injection, but the fluctuation level remained similar.

Commentary by Dr. Valentin Fuster
2018;():V007T09A048. doi:10.1115/IMECE2018-86618.

Pneumatic non-contact holders have been put to practical use for transporting semiconductor wafers and foodstuffs (hereafter “workpiece”) in manufacturing processes. The two main types of pneumatic non-contact holder are the Bernoulli and vortex types. In our previous study, we used a Bernoulli-type non-contact holder to achieve full non-contact holding by attaching a diffuser, but the workpiece underwent irregular rotation. With a vortex-type holder, this rotation could be prevented by generating two vortex flows with opposite rotations. However, the workpiece tended to slip away from the holder so that a guard structure was required, which introduced point contact with the guard into the holding process. This study’s purpose was to create a holder that is fully non-contact and does not cause workpiece rotation. By combining both the Bernoulli and vortex types, we succeeded in holding a workpiece without both contact and rotation.

Commentary by Dr. Valentin Fuster
2018;():V007T09A049. doi:10.1115/IMECE2018-86672.

Previous investigations [1–3] on the effects of rotating cylinder with either a smooth surface or cylinders with different surface geometries, placed at either the leading or the trailing edge of a symmetric airfoil on its aerodynamic parameters have shown that rotation at the leading edge does not provide significant lift, while placing the rotating cylinder at the training edge results in more than 20% increase in lift at all angles of attack (AOA) investigated. Increasing the rotation rate (α), the ratio of tangential velocity at the surface of the cylinders (Uτ) to the free stream mean velocity (U), increases the lift and grooved cylinders produced more lift than the smooth cylinder. There is an increase in drag when the rotating cylinder is placed at the trailing edge of the airfoil. Here we performed unsteady numerical investigations of a rotating wire-wrapped cylinder, placed in steady flow with α varied between 0 and 2. The free stream mean velocity was constant at 10 m/sec. and the smooth cylinder diameter was 5 cm, which corresponds to an approximate Reynolds number of 3.2 × 104. The wire wrapped had a wire diameter of 5 mm and the ratio of pitch spacing to the cylinder diameter was 1. The wire was wrapped tightly around the entire cylinder. The cylinder has a length to diameter ratio of 20. The rotation rate (α) ranged from 0.5 to 2.0. Results indicate wire-wrapped rotating cylinder produce higher lift than the rotating smooth cylinder and at α equal to 2, the lift for the wire-wrapped cylinder is nearly 150% of the lift of the smooth cylinder. However, wire-wrapped cylinder has higher drag force at higher rotation rate. At α = 2, the lift to drag ratio for the smooth rotating cylinder is 3.89, while the corresponding value for the rotating wire-wrapped cylinder is 3.54. Details of the flow indicates wire-wrapping reduces coherency and increases phase angle of vortices, resulting in increased lift.

Topics: Wire , Cylinders
Commentary by Dr. Valentin Fuster
2018;():V007T09A050. doi:10.1115/IMECE2018-87207.

The flow in annular gap with a restrictor mounted on outer cylinder is numerically simulated based on the hybrid Reynolds Averaged Navier-Stokes (RANS)/Large eddy simulation (LES) model. In stationary inner cylinder case, the pressure drop, mean axial velocity profiles and characteristic length scale of the recirculation zones are analyzed. Then the effects of rotating inner cylinder on the axial pressure distributions and the size of recirculation regions are examined. With the increase of rotating Reynolds number, the pressure loss of flow past the forward-backward step pair is greatly increased. Meanwhile, the transient pressure difference between the upstream inlet and downstream outlet gradually becomes fluctuating periodically due to the vortex shielding at the edge of backward step regularly. And the amplitude of the fluctuating pressure difference is comparable to its mean value. Moreover, the size of recirculation regions is reduced with the rising azimuthal Reynolds number, resulting from the interacting with enhanced Taylor vortices.

Commentary by Dr. Valentin Fuster
2018;():V007T09A051. doi:10.1115/IMECE2018-87285.

A special structure named auxiliary impeller is designed in the large capacity canned-motor pump to improve the performance of inner loop cooling system. The structure is set on the rotor shaft using the center hole as the inlet conduit and four holes perpendicular to the center hole as the blade channels. The auxiliary impeller is driven by the rotor shaft of the motor and functions as a centrifugal pump. The inner coolant circulates in the clearance of the pump under the effect of centrifugal force generated by the impeller. In this paper, the output pressure of the auxiliary impeller at different rotational speeds is investigated by numerical simulation. Three geometric parameters including the diameter of the inlet channel, the diameter of the blade flow channel, and the rotating radius are considered in the research. The pressure drop curves of the auxiliary impeller at different rotational speeds are drawn and a mathematical model is given to interpret it. The results show that both the three geometric parameters have influence on the output performance of the auxiliary impeller, and the diameter of the blade channel and the length of the rotating radius are the primary factors.

Commentary by Dr. Valentin Fuster
2018;():V007T09A052. doi:10.1115/IMECE2018-87833.

There are several industrial applications in which two phase solid-gas flows are involved. At times, pipe junctions are involved where flow split takes place. Present study consists of experimental investigation of turbulent gas-solid two-phase flow through horizontal pipe junctions. The effects of air flow rate, branch diameter and pipe orientation at junctions are investigated on mass fraction, phase split and solid particles distribution across the junctions. Silica powder, in the monodispersed size of 15 μm was injected into the pipelines by a micro-feeder. The powder was entrained in an air flow which passed horizontally through a long straight channel of circular pipe with T and Y junctions. The main pipe was 51mm in diameter while the inlet superficial velocity of gas was varied from 5 m/s to 13.5m/s. The particles mass concentration was measured by the aerodynamic particle sizer (APS). Experimental results showed that solid phase split followed air flow split while decreasing the inlet air velocity caused major decrease in the mass fraction at junction pipe. The orientation of junction pipe has a significant effect on the flow behavior along the pipe. These results indicate that the behavior of solid particles is a complex phenomenon in pipe flows.

Commentary by Dr. Valentin Fuster
2018;():V007T09A053. doi:10.1115/IMECE2018-87866.

A standard high-solids vessel (SHSV) concept design approach using pulse jet mixers (PJM) has been proposed by the US Department of Energy (DOE) for the Hanford Tank Waste Treatment and Immobilization Plant (WTP) as a potential replacement for several vessels that will be used to process highly radioactive waste. To assist with the evaluation of the SHSV concept, at DOE’s direction, the WTP Project recently completed qualification testing of the SHSV PJM mixing system to verify the design. Testing of the SHSV design, conducted at full scale, was split into two phases. The first phase of testing developed PJM controls that supported all operational modes under a set of most adverse fluid conditions. The second phase of testing used the PJM operating strategy, established during the first phase, to perform qualification testing to verify that the mixing system design supports the transfer, de-inventory, throughput, and sampling functional requirements of the SHSV. The different control methods that were used to operate PJMs in simulants exhibiting Newtonian and non-Newtonian rheological properties with high solids loading are presented.

The PJM system of the SHSV uses six pulse tubes distributed in a circular array. Each pulse tube (3000 liters nominal volume) is connected to a jet pump pair (JPP) by means of an air link line. The JPP powers the PJM operation by applying a vacuum to refill the PJM (suction phase), pressurizing the PJM to discharge the pulse tube content at a target velocity (drive phase), and releasing the compressed air to allow the PJM to depressurize into a ventilation system (vent phase) designed for contaminated air. A PJM control system was developed to maximize the PJM operation and minimize potential impact to the structural integrity of the vessel. The experimental results showed effective control of the system parameters. The system response demonstrated reliable control of the drive set pressure, the drive time, and synchronization. The PJM control system design also proved robust in mobilizing settled solids.

Topics: Testing , Pulsejets
Commentary by Dr. Valentin Fuster
2018;():V007T09A054. doi:10.1115/IMECE2018-87894.

Numerical investigations of using two different turbulence models of K-ε and K-ω on mixing characteristics of two confined jets in a crossflow at supercritical pressure have been performed. The confined jets were at 180 degrees from each other injecting into a round tube. The jet to crossflow mass flows ratio, r, was 2.96. Reynolds Averaged Navier Stokes (RANS) equations were solved using Siemens PLM CCM+ software. Results indicate higher mixing rate with K-ω turbulence model. Higher vorticity and lower turbulent kinetic energy are observed with k-ω turbulence model. Increased mixing indicate reduced velocity and pressure gradients and cooler fluid toward the tube wall.

Commentary by Dr. Valentin Fuster
2018;():V007T09A055. doi:10.1115/IMECE2018-88564.

Offshore petroleum production operations pose a unique set of challenges. A common undesirable phenomenon that occurs in these multiphase flow systems is known as slug flow. Slug flow is an oscillatory flow regime that creates large bullet shaped bubbles (also known as Taylor Bubbles) followed by large slugs of liquid. This high-rate alternation of liquid and gas production volumes in the surface facilities causes severe pressure oscillations. These oscillations adversely affect the structural health and individual components. A bench-scale closed flow loop was built with capabilities of measuring pressure and flow rates at different relevant sections. PID control strategy to mitigate the harmful effects of slug flow regime showed promise, although the tests were performed in the low pressure conditions of bench scale setup. The sensors and valve were programmed with MATLAB® to provide real time analysis, and a PID controller was utilized to adjust the back pressure. Initial experimental data and visual observation provided better understanding of slug flow regime and some quantitative data was obtained through image processing. Theoretical estimates of Taylor bubble velocities were found to be in agreement with presented observations. Further experiments are being carried out to gather data and showcase this model to develop better multiphase flow control strategies.

Topics: Slug flows
Commentary by Dr. Valentin Fuster
2018;():V007T09A056. doi:10.1115/IMECE2018-88565.

Slug flow is a major problem to the structural integrity and production equipment in offshore production platforms. Pressure oscillations due to the alternation of liquid and gas phases in slug flow regime can cause fatigue on the structural components of the platform. Also, the intermittent high flow rates can cause adverse effects on the production equipment.

A 28-foot pilot scale model was constructed to simulate the riser on offshore platforms. Three pressure sensors were attached to the model to monitor and record pressures in the riser during operations. A PID control strategy was utilized to regulate the pressure oscillations in the system by use of a linear actuated valve. Similarity between the pressure signals in the pilot scale model is qualitative when compared to actual pressures observed in an offshore riser system. A MATLAB® GUI was designed to allow for manipulation of the valve and allow for instant graphing of data for real time visualization of the pressure signals.

Pressure oscillations during slug flow with “no control” vary greatly and result in natural vibrations of the designed system. By pinching down on the choke valve to a designated opening, the back pressure in the riser increased, thereby slowing down the liquid slugs. However, an increase in the magnitude of the higher frequency oscillations can have adverse effects on the system. With the implementation of an active control, such as a linear actuated valve, a better control of back pressure on the riser and reduction in the magnitude of the higher frequency oscillations on the system is achieved.

Topics: Slug flows
Commentary by Dr. Valentin Fuster

Fluids Engineering: Microfluidics 2018: Fluid Engineering in Micro- and Nanosystems

2018;():V007T09A057. doi:10.1115/IMECE2018-86085.

Air bearing is future main supporting way of high-speed machinery such as turbocharger, micro gas-turbine engine. Foil bearing is a new type of air bearing which is lubricated by the thin-film air with its self-adapting elastic foil structure. It has many significant advantages such as non-pollution, longer working life, higher reliability, and lower friction loss. Different from foil journal bearing, in present the study of foil thrust bearing is extremely insufficient, especially about how to accurately predict the pressure distribution and efficiently improve the bearing capacity. The pressure distribution prediction of foil thrust bearing air film directly impacts the bearing stiffness and damping design, and then influences bearing capacity. The Reynolds equation commonly used to do such estimation is not accurate enough since the influence of temperature on air property parameters is ignored. The inaccurate prediction leads a catastrophic reduction to the bearing performance. In order to solve this problem, we propose a model to accurately predict the pressure distribution and capacity of foil thrust bearing using CFD method, as well estimating the relationship between air film clearance thickness, rotation speed, environment temperature and the capacity. Firstly, we simulate the pressure distribution of air film and then evaluate the simulation result by constrained experiments. We also correct the simulation by using modified air parameters obtained from experiment. The experimental results indicate our corrected simulation model is accurate with error less than 4%. Secondly, we compare simulation and experiment pressure results under different conditions. The model accuracy sensitivity varies within 10% under different rotation speed, air film clearance thickness and environment temperature. Finally, we use corrected model to analyze capacity impact parameters. We find the capacity of bearing increases with the decreasing of average air film clearance thickness under fixed speed of the thrust disc. The smaller clearance thickness is, the more influence its variation has on the bearing capacity. Meanwhile, the capacity of the bearing decreases with the reducing thrust disc speed under constant clearance thickness, and it decreases more obviously in the lower speed. The capacity reaches its largest under 200 °C and it falls with the increases or decreases of environment temperature. The model in this paper provides important theoretical foundation when designing the stiffness, damping and temperature control of each bearing area.

Commentary by Dr. Valentin Fuster
2018;():V007T09A058. doi:10.1115/IMECE2018-86289.

Microfluidic applications may involve the control of flows through a series of junctions. For example, flow branching is typically used to deliver specific quantities of fluid to various locations and converging flows are associated with mixing processes. The shape of the fluid interface of the converging flows at and downstream of the flow junction is the focus of this study. In particular, we investigate the transition from planar stratified flow to annular flow. We report results for microchannel configurations which have a main channel and an intersecting (at 90 or 45 degrees) daughter channel. Two 90 degree channels are investigated, one with cross sectional dimensions 129 × 100 um and the other 200 × 100 um. The 45 degree channel dimensions are 161 × 100 um. We compare flows of water over various Reynolds numbers (based on total flow) of 5–400. Flow visualization is achieved using confocal fluorescence microscopy. Flow modules are fabricated using soft lithography techniques and are enclosed by bonding plasma cleaned glass slides to the PDMS module. At lower Reynolds numbers, e.g., < 20, stratified flow is achieved with some curvature at the interface. As the Reynolds number increases, the flow transitions to have large degrees of curvature and eventually into annular flow. This transition is influenced by Reynolds number, flow ratio (daughter/total flow), channel geometry (cross section) and configuration (45 vs. 90 degrees). Flow regime plots are produced for all microchannel configurations. This study should provide insight into intersecting microfluidic flows when the Reynolds number is high enough to produce a non-planar fluid interface at the junction.

Commentary by Dr. Valentin Fuster
2018;():V007T09A059. doi:10.1115/IMECE2018-86602.

In this work, formation water drops as a Newtonian fluid in different bulk fluids are investigated. A MATLAB code has been developed to process the images taken via a high speed camera in the lab to measure the contact angle of drop, as well as the drop’s diameter and volume at different stages of formation. It is found that the water drop shows similar behavior when they shaped in the liquid phase bulk fluid with different properties while the drop formation’s behavior is substantially different when water drops are formed in the gas bulk fluid. In addition, it is tried to predict the frequency of drop formation at different flow rates with regard to the inertial and surface tension forces applied to the dispread fluid.

Topics: Fluids
Commentary by Dr. Valentin Fuster
2018;():V007T09A060. doi:10.1115/IMECE2018-86676.

With the advance of microfluidic platforms and due to the need to solve different implications that still exist on the transport of electrically conducting fluids, the analysis on strategies in micropumps that involve a simplicity in its structure, absence of mechanical moving parts, flow reversibility and low power requirement is current. Therefore, the present investigation contributes with the analysis of the combined magnetohydrodynamic/pressure driven flow of multilayer immiscible fluids in a microchannel formed by two parallel flat plates. The mathematical model is based in a steady fully developed flow and the pumped fluids follow the power law model to describe the pseudoplastic fluids rheology, while magnetic effects on the flow are given from the Lorentz forces. The velocity profiles and flow rate are obtained in the limit of small Hartmann numbers by solving analytically a closed system of ordinary differential equations, together to the corresponding boundary conditions at the solid-liquid interfaces in the channel walls and at the liquid-liquid interfaces between the fluid layers. The results show that the flow field is controlled by the dimensionless parameters that arise from the mathematical modeling being a parameter that indicates the competition between pressure to the magnetic forces, magnetic parameters related to Hartmann numbers, viscosities ratios between the fluids, flow behavior indexes and the dimensionless position of the liquid-liquid interfaces.

Commentary by Dr. Valentin Fuster
2018;():V007T09A061. doi:10.1115/IMECE2018-86980.

The recirculating wake behind the obstacle at moderate Reynolds numbers was devoid of particles, this was discovered by Haddadi et al. (J. Fluid Mech., 2014). However, only one obstacle and narrow Reynolds numbers were considered in their work. In this work, we constructed more confined environment, where the suspensions of solid fraction 0.25% with different particle diameters of 1, 5 and 10 μm flow past the critical confined low-aspect-ratio cylinder arrays (H/D = 0.3) with different arrangements were experimentally carried out. Reynolds numbers performed in the experiments ranged from 14∼550, and different flow patterns were observed. It was found that particles could flow into the region behind cylinder at low flow rate. Then, particle-depleted wake zone was formed behind the cylinder when increasing Re, which is similar with reported literature. It was interesting to find that when increasing Re further, the particles could flow into the recirculating wake zone behind cylinder. We generalized the particle behavior behind cylinder as from “entry” to “particle-free” and to “re-entry”. Additionally, the influence of different layout modes with inline and staggered cylinder arrays were also investigated. We found the particle-depleted wake zones behind the in-line cylinder array were larger than the one of the staggered cylinder array as the velocity were the same at “particle-free” stage. The in-line cylinder array possessed higher ability of allowing 1 μm particles to fill with the recirculating wake, whereas there were always existing particle-free zones in the core of recirculating wake of staggered cylinder array at “re-entry” stage. In order to understand particle-free mechanism better, microparticle image velocimetry (μPIV) technique was utilized to quantitatively measure the flow fields of in-line and staggered arranged cylinders. The obtained fluorescence pictures demonstrated that few particles flow into the zone behind cylinder at the “particle-free” stage, and fluorescence particles can flow into the wake at “re-entry” stage. That is, fluorescence particles also experienced the stages from “entry” to “particle-free” and to “re-entry”.

Commentary by Dr. Valentin Fuster
2018;():V007T09A062. doi:10.1115/IMECE2018-87387.

Dispersion of nanoparticles in pure fuels alters their key fuel physical properties, which could affect their atomization process, and in turn, their combustion and emission characteristics in a combustion chamber. Therefore, it is essential to have a thorough knowledge of the atomization characteristics of nanofuels (nanoparticles dispersed in pure fuels) to better understand their latter processes. This serves as the motivation for the present work, which attempts to gain a good understanding of the atomization process of the alternative, gas-to-liquid (GTL), jet fuel based nanofuels. The macroscopic spray characteristics such as spray cone angle, liquid sheet breakup, and liquid sheet velocity are determined by employing shadowgraph imaging technique. The effect of nanoparticles weight concentration and ambient pressures on the spray characteristics are investigated in a high pressure-high temperature constant volume spray rig. To this end, a pressure swirl nozzle with an exit diameter of 0.8 mm is used to atomize the fuels. The macroscopic spray results demonstrate that the nanoparticles dispersion at low concentrations affect the near nozzle region. The spray liquid sheet breakup distance is reduced by the presence of nanoparticle due to the early onset of disruption in the liquid sheet. Consequently, the liquid sheet velocity in that spray region is higher for nanofuels when compared to that of pure fuels. Also, the ambient pressure has a significant effect on the spray features as reported in the literature.

Topics: Jet fuels , Sprays
Commentary by Dr. Valentin Fuster
2018;():V007T09A063. doi:10.1115/IMECE2018-87832.

Many processes rely on wetting of liquids on surfaces. The way a liquid wets a solid depends on chemistry, geometry, and local energy inputs. Low-frequency surface vibrations can effect wetting changes prompted by droplet oscillations. High-frequency (ultrasonic) surface vibration can also cause a liquid to wet or spread out on a solid, but governing mechanisms are relatively uncharacterized. To investigate, droplets are imaged as they vibrate on a hydrophobic surface over different high frequencies (> 10 kHz). Wetting transitions occur abruptly over a range of parameters, but coincide with surface resonance modes. The wetting change is proportional to droplet volume and surface acceleration, and remains after cessation of vibration, however new droplets wet with the original contact angle. Wetting control has various industry applications, and understanding these basic phenomena will help develop a deeper understanding of how ultrasonic vibration can be utilized to tune the behavior of liquids on any surface.

Topics: Wetting , Vibration
Commentary by Dr. Valentin Fuster
2018;():V007T09A064. doi:10.1115/IMECE2018-87860.

Many important processes depend on the wetting of liquids on surfaces. Wetting is commonly controlled through material selection, coatings, and/or surface texture, however these means are sensitive to environmental conditions. Some “hydrophobic” fluoropolymer coatings are sensitive to extended water exposure as evidenced by declining contact angles and increasing contact angle hysteresis. Understanding degradation of these coatings is critical to processes that employ them. To accomplish this, contact angle measurements were taken before, during, and after slides coated with FluoroSyl 3750 or Cytop were submerged in water, or vibrated while covered in water. Both methods demonstrated similar changes in advancing contact angle though vibration increased degradation rates significantly. However, it does not simply accelerate the process as different trends are apparent in receding contact angles. The FluoroSyl 3750 showed no clear degradation under either condition. Surface profilometry did not detect any surface morphology differences that might cause contact angle change.

Topics: Coatings , Water
Commentary by Dr. Valentin Fuster
2018;():V007T09A065. doi:10.1115/IMECE2018-88054.

This work investigates the effect of negative dielectrophoresis (DEP) on polystyrene particles inside an evaporating DI water droplet on a PDMS surface. Deposition patterns of actuated droplets transitioned from a scalloped rings to a striped deposition pattern as the particle diameter increased from 20 nm to 1 μm. Increased particle size dramatically increases the negative DEP force on particles that push them toward the lower field gradient expected in fluid between active electrodes. Interestingly, deposition patterns became more uniform when particle diameter was increased to 5 μm. This uniform pattern appears to be due to interfacial trapping as the diffusion rate of the large particles was significantly slower than the velocity of the descending interface. This work suggests that DEP can be used to control deposition patterns left by evaporating colloidal droplets, but further work examining the electric field gradient inside the droplet is required to determine if this technique can be applied to a wider range of particle sizes.

Commentary by Dr. Valentin Fuster

Fluids Engineering: Posters

2018;():V007T09A066. doi:10.1115/IMECE2018-86363.

Laser welding is used to join metals of small thickness. The heat affected zone in this process is very small and the temperature gradients encountered are very large (of the order of 104K/mm). We have used numerical methods to analyze the effect of various parameters. For the present study, an in-house C code was developed to model the laser welding process. A Finite Volume based discretization was done and a Semi-Explicit method was used to solve the governing equations. Conduction mode heat transfer was considered by assuming no vaporization of the molten metal. The effect of various parameters like beam intensity and beam radius were studied on the weld dimensions. The beam intensity was varied from 5.2KW to 15KW while the beam radius was varied from 0.14mm to 0.35mm. The effect of welding angle was also studied on the weld dimensions. The welding angles used for the study were 0°, 26.5°, 45° and 56°. It was found that the weld width and depth increased with an increase in beam intensity and a decrease in beam radius, while the weld depth decreased with an increase in welding angle. The change in heat transfer and fluid flow was also studied by varying these parameters.

Commentary by Dr. Valentin Fuster
2018;():V007T09A067. doi:10.1115/IMECE2018-87606.

Jets produced by the interaction of collapsing cavitating bubbles containing high-pressure gases can be utilized for wide variety of applications e.g. particle erosion, medical purposes (lithotripsy, sonoporation), tannery effluent treatment, etc. Among the many parameters, this jetting is largely influenced by spatial orientation of bubbles, their times of inception, relative bubble size ratio. In this context, multiple cavitating bubbles are able to generate numerous simultaneous jets, under suitable conditions, hence operating over a wider coverage area. Such multi-bubble arrangements can go a long way in enhancing the erosive impact on a target location even at cryogenic temperature (< 123 K) and hence necessitate investigation.

In this paper, different configurations of multiple-bubble interactions are numerically simulated to examine jets directed towards a target location (fictitious particle, cell etc.) using computational fluid dynamics. No phase change is considered and the effect of gravity is neglected. The transient behaviour of the interface between the two interacting fluids (bubble and ambient liquid) is modelled using VOF (volume of fluid) method.

In this paper, results obtained for different bubble configurations through numerical simulation are validated against suitable literature and further explored to assess the resulting jet effects. The time histories of interacting bubbles are presented and the consequent flow-fields are evaluated by the pressure and velocity distributions obtained. The same calculation is repeated in cryogenic environment and the results are compared. An attempt is made to approach towards an optimum arrangement and conditions for particle erosion.

Topics: Bubbles , Jets
Commentary by Dr. Valentin Fuster
2018;():V007T09A068. doi:10.1115/IMECE2018-88343.

Cryogenic turboexpanders for nitrogen refrigeration and liquefaction cycles operating near liquefaction conditions are vulnerable to droplet formation. The turboexpander must be devoid of any traces of droplets, as this may cause damage to the blades and also result in performance deterioration. Hence, a multiphase flow analysis was conducted, based on the droplet condensation model in Ansys CFX®, to identify any possible droplet sites and its nature of propagation. A single-phase steady state simulation of the turboexpander was performed initially to identify the regions susceptible to droplet formation, followed by a multiphase analysis to study the flow field behavior and to characterize the droplet nucleation and growth. It has been observed that the low-pressure regions like vortices and wakes are susceptible to sub-cooling and thereby in droplet formation. Also, major geometrical parameters that affect the droplet nucleation have also been identified.

Commentary by Dr. Valentin Fuster

Fluids Engineering: Symposium on CFD Applications for Optimization and Controls

2018;():V007T09A069. doi:10.1115/IMECE2018-86332.

Large Eddy Simulations (LES) are performed to investigate the coherent structures in flows past a single and an array of tandem plates. Lagrangian coherent structures (LCS) are used to investigate the nonlinear vortex dynamics of flow past a single plate. The Finite-Time Lyapunov Exponent (FTLE) is calculated using the velocity data obtained from Large Eddy Simulations (LES). All simulations are conducted at Reynolds number of 50,000. LCS for a single plate is presented in this study to elucidate and comprehend highly turbulent flow interactions in these flows. The LCS is compared against most commonly used Eulerian structures which are contours of the vorticity and the Q-criterion. The FTLE fields reveal much clearer turbulent structures compared to the Eulerian structures. FTLE better describes the evolution of larger scale eddies. The Q-criterion of flows past an array of plates is also presented.

Commentary by Dr. Valentin Fuster
2018;():V007T09A070. doi:10.1115/IMECE2018-86480.

While Reynolds-averaged simulatons (RAS) have found success in the evaluation of many canonical shear flows, and moderately separated flows, their application to highly separated flows have shown notable deficiencies. This study aims to investigate these deficiencies in the eddy-viscosity formulation of four commonly used turbulence models under separated flow in an attempt to aid in the improved formulation of such models. Analyses are performed on the flow field around a wall mounted cube at a Reynolds number of 40,000 based on the cube height, h, and free stream velocity, U0. While a common occurrence in industrial applications, this type of flow constitutes a complex structure exhibiting a large separated wake region, high anisotropy, and multiple vortex structures. As well, interactions between vortices developed off of different faces of the cube significantly alter the overall flow characteristics, posing a significant challenge for the commonly used industrial turbulence models. Comparison of mean flow characteristics show remarkable agreement between experimental values and turbulence models which are capable of predicting transitional flow. Evaluation of turbulence parameters show the general underestimation of Reynolds stress for transitional models, while fully turbulent models show this value to be overestimated, resulting in completely disparate representations of mean flow structures between the two classes of models (transitional and fully turbulent).

Commentary by Dr. Valentin Fuster
2018;():V007T09A071. doi:10.1115/IMECE2018-86584.

Heavy commercial vehicles due to their un-streamlined body shapes are aerodynamically inefficient due to higher fuel consumption as compared to passenger vehicles. The rising demand and use of fossil fuel escalate the amount of carbon dioxide emitted to the environment, thus more efficient tractor-trailer design becomes necessary to be developed. Fuel consumption can be reduced by either improving the driveline losses or by reducing the external forces acting on the truck. These external forces include rolling resistance and aerodynamic drag. When driving at most of the fuel is used to overcome the drag force, thus aerodynamic drag proves an area of interest to study to develop an efficient tractor-trailer design. Tractor-trailers are equipped with standard add-on components such as roof defectors, boat tails and side skirts. Modification of these components helps reduce drag coefficient and improve fuel efficiency. The objective of this study is to determine the most effective geometry of trailer add-on devices in semi-truck trailer design to reduce the drag coefficient to improve fuel efficiency and vehicle stability.

The methodology consisted of CFD analysis on Mercedes Benz Actros using ANSYS FLUENT. The simulation was performed on the tractor-trailer at a speed of 30m/s. The analysis was performed with various types of add-on devices such as side skirts, boat tail and vortex generators. From the simulation results, it was observed that addition of tractor-trailer add-on devices proved beneficial over modifying trailer geometry. Combination of add-on devices in the trailer underbody, rear and front sections was more beneficial in reducing drag coefficient as compared to their individual application. Improving fuel efficiency by 17.74%. Stability of the tractor-trailer is improved due to the add-on devices creating a streamlined body and reducing the low-pressure region at the rear end of the trailer.

Commentary by Dr. Valentin Fuster
2018;():V007T09A072. doi:10.1115/IMECE2018-86629.

Automotive industry in continuously expected to produce more fuel-efficient vehicles. Increasing fuel prices and environmental concerns such as emission of CO2 are two areas in vehicle design improvement. There are multiple factors that affect the fuel economy such as rolling resistance, aerodynamic drag, and weight of the vehicle. As the speed of the vehicle increases, aerodynamic drag force becomes the dominating factor affecting the fuel consumption. This aerodynamic drag is a result of the low-pressure region created at the rear end of the vehicle. This low-pressure region is due to the relative square shape of the vehicle at the rear end which generates vortices.

This project aims to investigate the effects of an underbody in reducing the aerodynamic drag forces and its effects on fuel usage. The underbody in vehicles is one such area in improving the aerodynamics of a vehicle which can have an impact on overall drag force.

Various underbody geometry modifications were carried out on a 3D model of Fiat 500 Electric and Gasoline versions to simulate the effect of underbody geometry on fuel consumption using the CFD simulation tool ANSYS Fluent. It was concluded that the underbody of vehicle influences the overall aerodynamic drag by 20%. Underbody geometry modification helps in reducing the fuel consumption by decreasing the overall aerodynamic drag of the vehicle.

Commentary by Dr. Valentin Fuster
2018;():V007T09A073. doi:10.1115/IMECE2018-86640.

Multiphase flow is commonly found in almost every process related to oil and gas industry. The precise prediction of the flow behavior is essential to provide safe and efficient hydrocarbon recovery. An accurate characterization of multiphase flow plays a major role in well design optimization and development of successful production and transportation facilitiess. Even though the hydrodynamic behavior of multiphase flow in various pipe geometries typically found in the industry has been widely studied, there is still very little known about the flow pattern and hydrodynamic conditions presented in horizontal annular geometry. Current work presents Computational Fluid Dynamics (CFD) simulation of two-phase oil-water flow in horizontal concentric annuli using different turbulence models and Eulerian-Eulerian continuous-disperse interphase drag model. Water was modelled as disperse phase, while oil was considered as continuous phase. Effect of water droplet diameter in the interphase model is extensively discussed in this paper. Results of the simulations are compared to the experimental data for a variety of liquid velocities and water cuts.

Commentary by Dr. Valentin Fuster
2018;():V007T09A074. doi:10.1115/IMECE2018-87075.

An optimization of modified shrouded impeller with a curved spacer to suppress the unsteady flow recirculation was pursed. Centrifugal pumps are required to sustain a stable operation of the system they support under all operating conditions. Effect of minor geometrical modifications on the flow inside the three dimensional impeller passages are yet not fully understood, leading to costly trial and error approaches in the solution of instability problems. The idea of using a curved spacer to enhance the specified centrifugal impeller characteristics was validated. This modification with positioning the successful curved spacer prototype model at the impeller inlet section provided a wider pressure operation range at both low and high flow rates in a high-speed centrifugal pump type.

Seven curved spacer models were numerically analyzed in combination with the same original closed type impeller. The research investigated the effects of each inlet curved spacer model on the impeller’s performance improvement. The flow field inside a centrifugal pump is known to be fully turbulent, three-dimensional, and unsteady associated with secondary flow recirculation and separation at the impeller’s inlet and exit section. The rotor-stator interaction mechanisms or other unsteady effects often influence the water flow. The present research addresses the problem of Net Positive Suction Head Required (NPSHR) increase due to flow recirculation at the impeller suction side. The three dimensional unsteady water flow inside different models were analyzed by using a 3-D Navier-Stokes code with a standard k-ε turbulence model. The computational domain consists of four main zones: inlet, impeller hub, vanes, and outlet. The measurements with test rig were conducted for the pump hydraulic performances and flow field in the impeller passages. The numerical simulation and experimental tests of prototype performance concluded:

(1) Positioning a 3-D curved spacer at the impeller inlet section has a great impact on the centrifugal pump performance.

(2) Favorite effects were achieved on impeller performance by separating the inlet flow region into two lanes.

(3) The curved spacer resulted in improvement of closed impeller inlet static and total pressure values.

(4) Q-ΔP-η data and flow structures in the impeller passages were analyzed.

Commentary by Dr. Valentin Fuster
2018;():V007T09A075. doi:10.1115/IMECE2018-87119.

Direct or inverse design methods for centrifugal pumps play an important role in investigating their performance. In this paper, a very low specific speed centrifugal pump impeller of ns = 9.5 (metric), three blades and 222° wrap angle. This pump was investigated using the direct design method to achieve the blade shape geometry and examine the blade angle distribution. As the blade angle progression affects the pump performance, four models with different blade angle distribution were used to perform the hydrodynamic and suction performance of the pump. The linear and non-linear derived correlation models were designed firstly using ANSYS-BladeGen module then studied numerically using ANSYS-CFX module to solve the three-dimensional Navier-Stokes equations. Validation of the numerical simulation of the investigated centrifugal pump was done using experimental data. Numerical results show that the change in the blade angle distribution has an influence on the blade wrap angle. Consequently, the variation in the blade wrap angle affects the pump head and the relative velocity distribution. The pressure gradient varies in the pump with changing the blade length. Using the velocity streamline and the velocity vector, the eddies existence and distribution in the blade suction side affect the relative velocity distribution and the pump performance. It was found that the blade with the smallest length decreases the pump head and have best velocity distribution.

Commentary by Dr. Valentin Fuster
2018;():V007T09A076. doi:10.1115/IMECE2018-87166.

Numerical simulations with the steady 3D RANS were performed on a 4-stage low speed research compressor (LSRC) with two typical configurations (a shrouded and a redesigned cantilevered stator of the third stator). The shrouded stator (SS) with 0.67% labyrinth seal clearance of the blade height is the prototype, and the cantilevered stator (CS) with 1.2% hub clearance of the blade height is the redesigned cantilevered stator. The fourth rotor that follows after the cantilevered stator was redesigned (RE) according to blade load and inlet flow angle changed based on the redesigned cantilevered stator. The overall performance of the 4-stage LSRC and the distribution of aerodynamic parameters along the blade height were compared between the prototype and the redesigned third stator. Flow characteristics of the third stator and fourth rotor were analyzed in detail. The results indicate that the flow characteristics below the 35% blade height are very different between the prototype and the redesigned due to the effect of leakage flow from seal cavity and hub gap, respectively. The stall margin of CS is 57% higher than SS. The efficiency of CS at the design point is 0.82% higher than SS. Through the redesigned process of R4, the stall margin of RE is 45% higher than CS and the efficiency of R4 is 0.6% higher on average over the entire operating range.

Topics: Compressors , Stators
Commentary by Dr. Valentin Fuster
2018;():V007T09A077. doi:10.1115/IMECE2018-87798.

A thrust bearing is a particular type of rotary bearing permitting rotation between parts but designed to support a predominately axial load. Part I of this study was submitted to ASME 5th Joint US-European Fluids Engineering Summer Meeting. It compared the experimental, TEHD and CFD results for a thrust bearing. Reasonable relative errors between these three results were observed. The outlet oil film thickness at low speeds and the inlet oil film thickness at high speeds as calculated using TEHD were found to be more accurate than their counterparts. Isothermal, non-deforming CFD was found to predict outlet film thickness accurately as thermal deformation has a lower impact in the outlet region. Isothermal and non-deforming CFD was also found to produce a qualitatively accurate film thickness and pressure distribution.

Experimental data from a second paper reported by the same authors in Part I, provides temperature measurements in two different pads and showed some variation of temperature from pad to pad. A thermal CFD, different from isothermal CFD in Part I, was performed in this Part II. Different data analysis methods will be included in Part II including a comparison of leading edge, mid-plane and trailing edge temperature at two loads, two speeds. 24 different speed-load combination TEHD cases and 12 CFD cases were run in Part II in addition to the 32 TEHD cases and 8 CFD cases in Part I.

Both TEHD and CFD underpredict the slope between temperature and shaft speeds. TEHD also underpredicts the slope between temperature and bearing loads while CFD can get an accurate slope between temperature and bearing loads. An improved inlet temperature model would fix the error between temperature and bearing load in CFD, and also can enable CFD to have the same accuracy as TEHD analysis for the temperature versus shaft speed relation. The inlet film thickness from both TEHD and CFD is underestimated. TEHD is more accurate than CFD in outlet film thickness, or minimum film thickness, which is a critical performance characteristic in fluid film thrust bearings. While CFD is more accurate than TEHD in inlet film thickness and power loss.

Commentary by Dr. Valentin Fuster
2018;():V007T09A078. doi:10.1115/IMECE2018-87990.

Simulation of turbulent boundary layers for flows characterized by unsteady driving conditions is important for solving complicated engineering problems such as combustion, blood flow in stenosed arteries, and flow over immersed structures. These flows are often dominated by complex vortical structures, regions of varying turbulence intensities, and fluctuating pressure fields. Pulsating channel flow is one such case that presents a unique set of challenges for newly developed and existing turbulence models used in computational fluid dynamics (CFD) solvers. In the present study, performance of the dynamic hybrid RANS-LES model (DHRL) with exponential time averaging (ETA) is evaluated against Monotonically Integrated Large Eddy Simulation (MILES) and a previously documented LES study for a fully developed channel flow with a time-periodic driving pressure gradient. Results indicate that MILES over predicts mean streamwise velocity for all forcing frequencies while the DHRL model with ETA provides a method for improved results, especially for the lower frequencies. It is concluded that a hybrid RANS-LES model with ETA is a useful alternative to simulate unsteady non-stationary flows but further work is needed to determine the appropriate filter width for ETA to significantly improve the predictive capabilities of the DHRL model.

Commentary by Dr. Valentin Fuster
2018;():V007T09A079. doi:10.1115/IMECE2018-88327.

A number of cars are found to have an unconventional radiator. The radiator is placed at the back of the car instead of front, for which the radiator does not get the incoming airflow to cool the engine down and the engine gets overheated very easily. In order to deal with this problem, a channel has been mounted at the top of the vehicle to navigate incoming air flow and direct it through the radiator to cool down the engine. Three channels are tested computationally with three different lengths, which indicates the different way of studying this problem. Transient state analysis has been performed. Each length has its own characteristics. For example, a longer channel creates little circulation but more axial flow towards the radiator, while shorter channel creates smooth but less axial flow towards the radiator. All these cases in the steady state have the same domain and will have similar inlet variables like velocity, shape, size, and position.

A transient state simulation, most of the circulation were shown in the left-mid plane especially in longer channels. Transient state gives more uniform flow distribution. For longer channels in transient case, the flow is symmetric and smooth, while the flow is not found symmetric for short channel. The results were all made and developed in ANSYS for the final design where the data were simulated.

Commentary by Dr. Valentin Fuster
2018;():V007T09A080. doi:10.1115/IMECE2018-88328.

Transient Scale Resolved Simulations, like the Detached Eddy Simulation, are currently seen to be the preferred modeling approach over the steady-state Reynolds Averaged Navier-Stokes (RANS) simulations for numerical investigations of external flow due to the former’s perceived capability of providing a more realistic flow field prediction. However, the latter approach is still a widely used methodology in road vehicle aerodynamic developments because of its faster turn-around time and cost-effectiveness. However, RANS models, like the SST k–ω, generally fail to produce well-correlated predictions. Studies reveal that good correlations with experiment cannot be achieved by simply refining the mesh when using the SST k–ω model. As such, this study explores the possibility of improving the prediction veracity by investigating the influence of a few selected model closure coefficients on the CFD prediction. This involves first identifying the effect of each individual model parameter on the prediction, and then formulating the best combination of the model closure coefficient values that yield the best correlation with the experiment. This procedure is applied to three different test objects: NACA 4412 airfoil at 12 degree angle of attack, the 25 degree slant angle Ahmed body, and a full-scale passenger road vehicle. Although some closure coefficients do not influence the CFD results much, the predictions are very sensitive to the choice of certain model constants, irrespective of the test object geometry. The study also shows that it is possible to formulate a combination of closure model coefficients that can produce very well correlated CFD predictions.

Commentary by Dr. Valentin Fuster
2018;():V007T09A081. doi:10.1115/IMECE2018-88332.

The automotive industry is one of the fastest growing industries worldwide with millions of vehicle productions and sales every year globally. Some of the vehicles have their engines in rear end, which means there is no incoming airflow from the front and the engine cannot cool down efficiently. The main aim of the research is to study the flow behavior for a duct that can detour the incoming air to the radiator for vehicles those have their engines located at the back. The duct collects the incoming air from the front of the vehicle and detour it to the engine located at the back. This helps in cooling down the engine in order to protect it from being overheated. The research is conducted to understand the detailed parameters to be accounted for while designing such a prototype. It is important to understand the essence of a cooling effect as the efficiency of the vehicle engine can only be maintained under a stable temperature. The research is important as it can be applied to diverse engineering problems. There are three cases for the experiment, each with different lengths. However, the inlet and outlet have identical dimensions for all three cases. There is a certain scale factor used to scale down the dimensions from a previously studied CAD model. These scaled down dimensions are then utilized to fabricate the prototype. Once the model has been constructed, a mesh is located at the outlet, which helps recording velocity magnitude and direction at each of the respective node of the mesh. One of the key elements of the research is to extensively understand the type of flow at different points of the duct and how they affect the efficiency of the design. For example, the curved parts where channels are installed along the length of the duct experience turbulent air flow. Hence, it is important to understand the influence of these flows on the efficiency of the design.

Commentary by Dr. Valentin Fuster
2018;():V007T09A082. doi:10.1115/IMECE2018-88613.

Due to the coastal wave actions, Louisiana coastline has been experiencing serious depletion of wetlands over decades. The loss of wetlands is threating the environment and the economic development of Louisiana. Therefore, breakwaters are designed to protect the coastline from coastal erosion and wetland losses by dissipating the energy of waves and changing the transport of sediment which is brought by the waves. The objective of this research was to give a numerical analysis of 2-dimensional breakwaters under wave actions and 3-dimensional breakwaters turbulence characteristics under coastal wave actions using CFD simulation. In this research, three breakwater structures are tested: a solid panel with no holes, a panel with three holes, and a panel with eight holes. The breakwater designs aim to allow sediment pass through the holes, to deposit and accumulate sediment at target areas, and to reduce wave actions. There were three different cases simulated with wave actions and without wave actions in this study, each case using a different panel design. The results of this study were mainly compared with the 2-dimensional CFD simulation analysis conducted previously to prove the accuracy.

Commentary by Dr. Valentin Fuster
2018;():V007T09A083. doi:10.1115/IMECE2018-88673.

Radial fans for industrial applications are very commonly operated with a spiral casing, also called volute. The function of the volute is to collect the air from the impellers outlet and to transport it to the fans outlet. In the volute the tangential velocity component of the impeller is transformed in a straight velocity component at the volute’s outlet. In the volute the static pressure is increased according to the cross sectional area of the volute. When the flow exits the impeller the flow rate is given basically by the radial velocity component times the outlet area of the impeller. In the volute, however, the flow rate is basically given by the tangential velocity component at the impeller exit and in the volute considering the conservation of angular momentum. Hence, there is only one operating point, i.e. the design point of the volute, where the flow rate in the impeller matches the flow rate in the volute. In the literature the design of the volute is performed at the design point only and the cross sectional area of the volute is usually computed distributing the flow rate linearly from the tongue to the exit of the volute.

In this work an extended theoretical approach was developed considering the design point flow rate and off design flow rates. At the design point, the properties of the specific impeller, i.e. it’s radial and its tangential velocity components at the impeller’s exit are considered to design the volute. Furthermore, also the off-design characteristics of the impeller, i.e. its radial and tangential velocity components are considered in the design process of the volute. The flow rates in the impeller and in the volute match only at the design point, at off-design points the flow rates in the impeller and in the volute are different. This has an important impact on the design process of impeller – volute units. Each volute has also to be matched to the specific impeller.

In the numerical part a usual volute was designed considering the properties of a particular impeller. The performance of the volute and of complete fan was investigated with the commercial Navier–Stokes Solver ANSYS CFX. A detailed analysis of the results and the flow conditions in volute as well as in the impeller-volute unit and a comparison with the results predicted by the new volute theory is given.

Commentary by Dr. Valentin Fuster
2018;():V007T09A084. doi:10.1115/IMECE2018-88674.

In order to investigate the impact of the gas temperature and its relative humidity on the performance of fans, the similarity laws for fans were extended and verified and numerical computations with the commercial CFD solver ANSYS CFX were performed. First the accuracy of the original fan laws was verified for different operating conditions. In a second step the influence of the temperature on the fan characteristics was investigated. Finally, to include the effect of the relative humidity multiphase simulations with air and water vapor were performed. Therefore, the relative humidity was analyzed for different gas temperatures. In such a way the full influence of the temperature and of the relative humidity on the performance characteristics of radial fans operating in drying plants was obtained. These numerical results have been analyzed in detail and compared with the results predicted by the presented extended similarity laws for turbomachines.

Topics: Temperature , Drying , Fans
Commentary by Dr. Valentin Fuster

Fluids Engineering: Symposium on Wind Turbines Aerodynamics and Control

2018;():V007T09A085. doi:10.1115/IMECE2018-86820.

An adaptable numerical scheme for the aerodynamic shape optimization of axisymmetric diffuser-augmented wind turbine shrouds is demonstrated in this work, using an asynchronous and parallel version of a Differential Evolution (DE) algorithm. The simulation of the incompressible flow field about each candidate geometry is succeeded by means of an in-house Computational Fluid Dynamics (CFD) solver, that has been developed based on the specially modified, by the artificial compressibility approach, Navier-Stokes equations, expressed in non-dimensional form, for 2D-axisymmetric frames of reference. The discretization of the computational domain is made with 2D hybrid unstructured meshes, composed by both triangular and quadrilateral elements, combined with a node-centered finite-volume scheme, while the Free-Form Deformation (FFD) technique is applied, for both the parameterization of the design geometry and the morphing of the computational mesh. The required data transfer between the DE algorithm and the CFD solver is accomplished with appropriate text files, while the parallel implementation is achieved utilizing the Message Passing Interface (MPI) library functions. Further acceleration of the optimization procedure is succeeded by the combination of the DE with surrogate models, in order to replace the costly CFD-based evaluations of the candidate solutions with fast, but approximate estimations of their cost function.

Commentary by Dr. Valentin Fuster
2018;():V007T09A086. doi:10.1115/IMECE2018-86823.

Nowadays a large interest in the public and private sector is dedicated in generating electricity using renewable resources. Thus, over 60,000 MW is produced worldwide by using the wind energy. These systems are generally composed of power plants formed from 2–3 to several tens, hundreds of wind turbines with rotating blades that reach heights over 160m. The number, the height, and the rotation of these wind turbines represent technical challenges for the radar system efficiency and accuracy. They should be assessed carefully, in each case, to ensure that it maintains an acceptable level of the air space surveillance capability. The research paper presents the influence of the wind power farms on the air radars especially in cases of surveillance area, both for the primary radars and the secondary radars. There are differences between the interference between the wind turbines and radars functioning, depending on the types of radars. In the last decades in Romania is a permanent effort to increase the number the wind farms built, or in the process of being built, but also referring at the number of wind turbines in these parks and their physical dimensions. This paper focuses on the effects of the wind farms on the radars efficiency, and their potential impact on the ability of airspace surveillance. This results in a concise and transparent reference guide for developers of wind farms when assessing the impact of wind turbines on aerial surveillance systems. Specialists are relatively unanimous in their opinion that, in order to make an assessment of the impact of the wind farms on the radars must be defined at least three areas corresponding to different levels of the technical expertise. They must be combined with the influence of the wind farms on the ability of the radar to fulfill the mission, why they were installed, assuming that it is necessary to create an exclusive protection area. First, are discussed briefly the principles of the radar’s operation, depending on their type: primary and secondary surveillance radars. Further, are estimated the induced reflections by the wind power plant on the radar system. If the number of false targets generated by the reflections from wind turbines is too big, so it exceeds the processing capacity of the radar, the operational capacity will suffer. There are presented some theoretical aspects, followed by some cases where the proper functioning of the primary and secondary radars is affected. The model is tested in field, at two different distances, with airplanes and helicopter flying at different altitudes, with radar placed near the wind power plant Fantanele – Cogelac, the biggest in Romania. Finally, is estimated the area necessary to assure proper functioning of radars. Some conclusions and references are presented.

Topics: Wind farms
Commentary by Dr. Valentin Fuster
2018;():V007T09A087. doi:10.1115/IMECE2018-87327.

The root region of small wind turbines experience low Reynolds number (Re) flow that makes it difficult to design airfoils that provide good aerodynamic performance and at the same time, provide structural strength. In the present work, a multi-objective genetic algorithm code was used to design airfoils that are suitable for the root region of small wind turbines. A composite Bezier curve with two Bezier segments and 16 control points (11 of them controlled) was used to parametrize the airfoil problem. Geometric constraints including suitable curvature conditions were enforced to maintain the airfoil thickness between 18% and 22% of chord and a trailing edge thickness of 3% of chord. The objectives were to maximize the lift-to-drag ratio for both clean and soiled conditions. Optimization was done by coupling the flow solver to a genetic algorithm code written in C++, at Re = 200,000 and for angles of attack of 4 and 10 degrees, as the algorithm was found to give smooth variation of lift-to-drag ratio within such a range. The best airfoil from the results was tested in the wind tunnel as well as using ANSYS-CFX. The experimental airfoil had a chord length of 75 mm and was provided with 33 pressure taps. Testing was done for both free and forced transition cases. The airfoil gave the highest lift-to-drag ratio at an angle of 6 degrees with the ratio varying very little between 4 degrees and 8 degrees. Forced transition at 8% of chord did not show significant change in the performance indicating that the airfoil will perform well even in soiled condition. Fixed trailing edge flaps (Gurney flaps) were provided right at the trailing edge on the lower surface. The lift and drag behavior of the airfoil was then studied with Gurney Flaps of 2% and 3% heights, as it was found from previous studies that flap heights of 1% or greater than 3% do not give optimum results. The flaps considerably improved the suction on the upper surface and also improved the pressure on the lower surface, resulting in a higher lift coefficient; at the same time, there was also an increase in the drag coefficient but it was less compared to the increase in the lift coefficient. The results indicate that Gurney flaps can be effectively used to improve the performance of thick trailing edge airfoils designed for the root region of small wind turbines.

Commentary by Dr. Valentin Fuster
2018;():V007T09A088. doi:10.1115/IMECE2018-88304.

Ram air turbine (RAT) is an emergency power source to supply power in case of the main engine and auxiliary engine lost power. Which can extract energy from airflow through rotating turbine. So it is important to investigate turbine aerodynamic performances. According to some type of RAT, we established a numerical model based on Navier–Stokes equation in rotating frames of reference. Calculation domain is divided into three fluid domains. All three regions are linked in the form of interface. Aerodynamic performance of RAT is simulated with computational fluid dynamics (CFD) soft. The extracted power and rotor power coefficient are analyzed under different running conditions. Next, we also investigate RAT aerodynamic performance at different pitch angle and turbine speed. The pressure and velocity distribution on the blade surface are studied. Besides, the method of multiple rotation frame (MRF) is used to simulate mixed flow field of the RAT which pitch angle is adjustable. The simulation results show that: turbine output power and rotor power coefficient can meet the needs of aircraft by adjusting the pitch angle under various operation conditions. The optimal operating point could be obtained by calculating RAT aerodynamic performance. The distribution of blade surface pressure and velocity could provide an important reference for the optimization of turbine blade designing. MRF can be used to calculate turbine aerodynamic performance.

Commentary by Dr. Valentin Fuster

Fluids Engineering: Young Engineers Paper (YEP) Contest

2018;():V007T09A089. doi:10.1115/IMECE2018-86549.

The current trend in the wind power market is to develop large diameter rotors in order to maximize the power extraction from the wind. Those rotors exhibit issues related to blade deflection and structural integrity that can be mitigated implementing design variations that were present on the early wind turbine designs, such as rotors with less than three blades located behind the tower in downwind configuration. This work assesses the aerodynamic performance of a downwind two-bladed wind turbine based on CFD simulations coupled with the Actuator Line Model (ALM). This design is compared with the MEXICO project upwind three-bladed wind turbine, for which experimental data is available. The simulations showed good agreement with measurements especially upstream the rotor and for higher inlet velocities. Furthermore, the downwind configuration was successfully modeled using ALM and the performance prediction of the turbines was physically accurate since realistic variations were obtained between the evaluated wind turbines and none of their performance coefficients exceeded Betz theoretical limit.

Commentary by Dr. Valentin Fuster
2018;():V007T09A090. doi:10.1115/IMECE2018-86610.

Reducing turbulent skin-friction drag is a subject of great interest due to the potential benefits. These benefits are reflected in applications such as aircraft and vehicles for which skin-friction drag constitutes a significant fraction of the total drag. For example, commercial airliners have up to 50% of their fuel consumption associated with turbulent drag. Thus, any drag reduction would result in substantial savings with regards to the operational cost of the airline industry. In this study, we investigated the effects of a spanwise body force on reducing skin-friction drag in turbulent channel flows. To this end, we performed direct numerical simulations (DNS) of turbulent channel flows with an applied spanwise body force. The body force consists of four control parameters: the amplitude of excitation, penetration depth, period of oscillation, and wavelength. A series of DNS were performed to investigate the effect of these parameters on drag reduction. We observed different levels of drag reduction and the magnitude of skin-friction varied considerably. The DNS results showed that the skin friction is reduced by as much as 20% with values for penetration lengths from 0.03 to 0.09 and periods between 10 and 20. An optimal combination of the four adjustable control parameters is yet to be concluded. In addition to skin-friction reduction, we found an intriguing observation from a time series of wall shear stress. When the wall shear stress is sufficiently lower than its mean value (i.e., low-drag intervals), the spanwise body force appears to significantly affect turbulent dynamics to make the wall shear stress not as chaotic as in other intervals. Specifically, the standard deviations of the peak-to-peak magnitudes of the wall shear stress during low-drag intervals are significantly lower than that of other intervals. This observation could be crucial in that it may lead to a further fundamental understanding of the drag reduction process. Moreover, it may aid in the development of more effective control schemes by way of anticipating that low-drag intervals are promising targets for drag reduction.

Commentary by Dr. Valentin Fuster
2018;():V007T09A091. doi:10.1115/IMECE2018-86937.

Y-shaped microfluidic channels have been built with Computer Numerical Control (CNC) and laser cutting manufacturing techniques. Fluid is delivered to each port via external syringe pumps. Each Y-shaped channel contains thermal inkjet (TIJ) resistors built using conventional microfabrication techniques. The resistors vaporize water and generate drive bubbles. This work focuses on utilizing TIJ technology as an active mixing technique in microfluidics. By varying the electrical firing frequency of the resistors, fluid was successfully mixed with an effective mixing length equal to the length of the TIJ resistor. As such, we demonstrate the use of TIJ resistors as a scalable, active mixing approach in microfluidics. A metric to characterize the extent of mixing using TIJ resistors was proposed and utilized. In addition, the fundamental framework of TIJ bubble dynamics with respects to mixing was assessed.

Commentary by Dr. Valentin Fuster
2018;():V007T09A092. doi:10.1115/IMECE2018-87089.

Non-contacting annular seals are used in rotating machinery to reduce the flow of working fluid across a pressure differential. Helical and labyrinth grooved seals are two types of non-contacting annular seals frequently used between the impeller stages in a pump and at the balance drum. Labyrinth seals have circumferential grooves cut into the surface of the rotor, the stator, or both. They function to reduce leakage by dissipating kinetic energy as fluid expands in the grooves and then is forced to contract in the jet stream region. Helical groove seals have continuously cut grooves on either or both the rotor and stator surfaces. Like labyrinth seals, they reduce leakage through dissipation of kinetic energy, but have the added mechanism of functioning as a pump to push the fluid back towards the high-pressure region. Previous work has shown that mixed helical-labyrinth seals with labyrinth grooves on stator and helical grooves on rotor or labyrinth grooves on rotor and helical grooves on stator have an approximately 45% lower leakage than an optimized helical groove seal with grooves just on the stator in a high pressure application. The primary objective of this study is to determine whether the same performance gains can also be achieved in a low pressure application. Simulations were run in ANSYS CFX for seal designs with a helical stator and labyrinth rotor. Several labyrinth design parameters including the number of grooves and the groove width and depth are varied while the helical variables such as the groove width and depth as well as helix angle are kept constant. The data obtained are analyzed using backward regression methods and various response plots to determine the relationship between the design parameters and mass flow and power loss. The optimized helical design was simulated and the axial pressure profiles of the designs were compared to analyze the mechanism of the mixed helical-labyrinth seal. Then, the same labyrinth seal designs were simulated for a labyrinth rotor and a smooth stator to determine whether the optimal number of grooves, groove width and groove depth change due to the helical stator. The findings of this study show the effectiveness of mixed helical labyrinth grooved seals for both low and high pressure cases, and thus their efficiency and reliability for numerous industrial applications.

Topics: Design
Commentary by Dr. Valentin Fuster
2018;():V007T09A093. doi:10.1115/IMECE2018-88797.

In this work, several different bioinspired filter geometries are proposed, fabricated, and tested in a flow tank. A novel approach is explored that mimics how filter-feeding fish efficiently remove small food particles from water. These filters generally take the form of a cone with water entering the large end of the cone and exiting through mesh-covered slots in the side of the cone, which emulates the rib structure of these filter-feeding fish. The flow in and around the filters is characterized and their ability to collect algae-scale, neutrally-buoyant particles is evaluated.

Filter performance is evaluated by using image processing to count the number of particles collected and studying how the particles are deposited on the filter. Results are presented in the form of particle collection efficiencies, which is a ratio of particles collected to the particles that would nominally enter the filter inlet, and images of the fluorescent particles deposited on the filter at different time intervals. The results show little sensitivity to the filters’ inlet geometries, which was the major difference between filters tested. Comparative results are also presented from a 2D CFD model of the filters generated in COMSOL. The different geometries may differentiate themselves more at larger Reynolds numbers, and it is believed that a fluid exit ratio, or ratio of inlet area to exit area, is the most critical filter parameter.

Field testing has demonstrated collection of real algae (i) with this bioinspired filter, and (ii) from a robot platform, but using a more conventional plankton net. The larger vision is to develop these filters and mount them on a swarm of autonomous surface vehicles, i.e. a robot boat swarm, which is being developed in parallel.

Topics: Filters
Commentary by Dr. Valentin Fuster

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