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ASME Conference Presenter Attendance Policy and Archival Proceedings

2016;():V001T00A001. doi:10.1115/IMECE2016-NS1.
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This online compilation of papers from the ASME 2016 International Mechanical Engineering Congress and Exposition (IMECE2016) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Advances in Aerospace Technology: Advanced Numerical Methods for Aerospace Structures and Materials

2016;():V001T03A001. doi:10.1115/IMECE2016-65557.

In this paper, we present a nonlocal lattice particle framework for modeling the brittle behaviors of both isotropic and anisotropic solid materials. Different from other continuum based models, the formulation of this lattice particle model is discrete and there is no spatial derivative involved. This avoids the singularity issues of discontinuous problems, which commonly exists in continuum based models. The model is also nonlocal that a discrete element can interacts with its neighbors up to certain distance. This nonlocality better solves some issues in other discrete models, such as fixed range of Poisson’s ratio. The modeling capability and accuracy are demonstrated using numerical examples.

Commentary by Dr. Valentin Fuster
2016;():V001T03A002. doi:10.1115/IMECE2016-65574.

The multi-objective optimization for a nested flying vehicle (NFV) of space science experiments is carried out aiming at the launch weight, frequency response and vacuum effect. The parametric model and finite element analysis are adopted to implement the structural analysis. The NFV is optimized to enhance the performance in the space environment where the lunch weight and structural strength are key constraints to concern about. The CAX software, analysis models and algorithms are integrated based on ModelCenter framework which makes modeling, analyzing and optimization more convenient and efficient. The optimizer of ModelCenter is chosen to optimize the structural performance of NFV, including the total mass, maximum deformation caused by vacuum environment and frequency response. As to validate the results, both weighting method with gradient optimization algorithm and Genetic Algorithm (GA) for multi-objective optimization are used. The optimization results of NFV verify the approaches proposed in this paper can improve the performance of NFV and apply to the finite element analysis model.

Commentary by Dr. Valentin Fuster
2016;():V001T03A003. doi:10.1115/IMECE2016-65645.

In the present work, a higher-order beam model able to characterize correctly the three-dimensional strain and stress fields with minimum computational efforts is proposed. One-dimensional models are formulated by employing the Carrera Unified Formulation (CUF), according to which the generic 3D displacement field is expressed as the expansion of the primary mechanical variables. In such a way, by employing a recursive index notation, the governing equations and the related finite element arrays of arbitrarily refined beam models can be written in a very compact and unified manner. A Component-Wise (CW) approach is developed in this work by using Lagrange polynomials as expanding cross-sectional functions. By using the principle of virtual work and CUF, free vibration and linearized buckling analyses of composite aerospace structures are investigated. The capabilities of the proposed methodology and the advantages over the classical methods and state-of-the-art tools are widely demonstrated by numerical results.

Commentary by Dr. Valentin Fuster
2016;():V001T03A004. doi:10.1115/IMECE2016-65842.

One considers a linear elastic composite material (CM, [1]), which consists of a homogeneous matrix containing the random set of heterogeneities. An operator form of the general integral equation (GIE, [2–6]) connecting the stress and strain fields in the point being considered and the surrounding points are obtained for the random fields of inclusions in the infinite media. The new GIE is presented in a general form of perturbations introduced by the heterogeneities and defined at the inclusion interface by the unknown fields of both the displacement and traction. The method of obtaining of the GIE is based on a centering procedure of subtraction from both sides of a new initial integral equation their statistical averages obtained without any auxiliary assumptions such as the effective field hypothesis (EFH), which is implicitly exploited in the known centering methods. One proves the absolute convergence of the proposed GIEs, and some particular cases, asymptotic representations, and simplifications of proposed GIEs are presented for the particular constitutive equations of linear thermoelasticity. In particular, we use a meshfree method [7] based on fundamental solutions basis functions for a transmission problem in linear elasticity. Numerical results were obtained for 2D CMs reinforced by noncanonical inclusions.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Advances in Aerodynamics

2016;():V001T03A005. doi:10.1115/IMECE2016-65676.

In hypersonic flight of reentry vehicles the radio blackout is a typical problem, in particular because it arises during a critical mission operation point. To mitigate this radio blackout the magnetic window concept is proposed. In this work a numerical model is presented to accurately simulate the effect of a magnetic field interacting with ionized plasma surrounding the vehicle. The numerical model is based on the MHD flow equations. Initially, the code is validated for pure hypersonic gas dynamics. Diverse high resolution spatial discretisation schemes, within a Finite Volume framework, are analyzed for robustness. Afterwards, the numerical code is further validated for MHD flows using the well-known Hartmann case. A very good comparison between numerical and analytical results is verified. This allows a proper validation of the method in terms of Lorentz force, in particular under low-magnetic Reynolds number conditions. A very tough test-case is finally computed, being typical of a reentry capsule geometry. The accuracy of the model is then verified for different applied magnetic fields.

Commentary by Dr. Valentin Fuster
2016;():V001T03A006. doi:10.1115/IMECE2016-66405.

In this study the development and assessment of an academic CFD (Computational Fluid Dynamics) code, named Galatea-I, is reported. The proposed solver employs the RANS (Reynolds-Averaged Navier-Stokes) approach, modified by the artificial compressibility method, along with the SST (Shear Stress Transport) turbulence model to predict steady or unsteady turbulent incompressible flow phenomena on three-dimensional unstructured hybrid grids, composed of prismatic, tetrahedral and pyramidal elements. Parallel processing and an agglomeration multigrid method have been included for the acceleration of the solver’s methodologies. Galatea-I is evaluated against a test case of the HiLiftPW-2 (Second High Lift Prediction Workshop). In particular, the low Mach number flow at incidence angle over the DLR-F11 aircraft configuration of Case 1 of the aforementioned workshop was examined; it considers a three-element wing with a leading edge slat and a trailing edge flap attached on a body pod, without including though any of the support brackets used in the wind tunnel experiments. The obtained results are close to the available experimental data, as well as the numerical results of other reference solvers, indicating the proposed methodology’s potential to predict accurately such low Mach number flows over complex geometries.

Commentary by Dr. Valentin Fuster
2016;():V001T03A007. doi:10.1115/IMECE2016-66495.

Active flow control by plasma actuators is a topic of great interest by worldwide scientific community. These devices are mainly used for boundary layer control in order to improve the aerodynamic performance of aerial vehicles. Plasma actuators are simple devices that produces a wall bounded jet which allow to control the adjacent flow without moving mechanical parts. Recently, new geometries have been proposed by different authors in an attempt to improve the performance of these devices. In this work, some of these new configurations will be studied and compared considering its ability for boundary layer control applications. Dielectric Barrier Discharge (DBD) plasma actuator, Plasma Synthetic Jet (PSJ) actuator, Multiple Encapsulated Electrodes (MEE) plasma actuator and Curved plasma actuator (or 3D plasma actuator) will be experimentally studied in this work. Plasma actuators power consumption was measured by two different experimental methods. Results for power consumption and power losses of different plasma actuators geometries were presented and discussed.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Advances in Beam, Plate, and Shell Theories

2016;():V001T03A008. doi:10.1115/IMECE2016-65644.

This paper presents a novel approach to deal with the analysis of composite aerospace structures with curved sections. The Carrera Unified Formulation is exploited to create hierarchical high-order beam models capable of detecting both local and global mechanical behaviors of composite structures. The blending function method is applied to introduce the exact shape of the cross-section boundaries into the mapping functions. Problems at both microstructure scale (fiber-matrix system) and macrostructure scale (whole components) can be studied with no lack of generalization. Several numerical examples of aerospace structures are included and the results are compared against those from the literature, as well as solid solutions obtained through the commercial software MSC Nastran. From this study, it is clear than the present formulation has demonstrated to be a powerful tool for the study of composite structures, enabling to obtain complex 3D-like solutions with a substantial reduction in the computational costs.

Commentary by Dr. Valentin Fuster
2016;():V001T03A009. doi:10.1115/IMECE2016-66681.

This paper presents the static analysis of tapered structures made of composite material using 1D models. These models are based on a one-dimensional formulation derived using the Carrera Unified Formulation (CUF). This formulation allows us to obtain 3D-like results thanks to the use of polynomial expansions to describe the displacement field over the cross-section. According to the types of expansion used, different classes of refined one-dimensional elements are obtained. In this work the Lagrange expansions were used. The use of LE models allows each structural component to bo considered separately; this approach is called component wise (CW). The thin-walled structures are usually made of composite materials, in particular, the aeronautical structures. For this reason, these kinds of structures are taken into account. The stress and displacement fields due to simple load cases have been obtained. The results have been compared with those obtained using commercial tools. The results show the capability of the present refined one-dimensional models to achieve results usually obtained by the use of solid models and therefore, with higher computational cost.

Commentary by Dr. Valentin Fuster
2016;():V001T03A010. doi:10.1115/IMECE2016-66771.

In the present study, a new trigonometric higher-order shear and normal deformation theory is proposed and implemented to investigate the free vibration characteristics of functionally graded material (FGM) plates. The present theory comprises the nonlinear variation in the in-plane and transverse displacement and accommodates, both shear deformation and thickness stretching effects. It also satisfies the stress-free boundary conditions on the top and bottom surfaces of the plate without requiring any shear correction factor. The governing equations are derived using the variational principle. The effective mechanical properties of FGM plates are assumed to vary according to a power law distribution of the volume fraction of the constituents. Poisson’s ratios of FGM plates are assumed constant. The numerical solution has been obtained using an efficient displacement based C0 finite element model with eight degrees of freedom per node. The computed results are compared with 3-dimensional and quasi-3-dimensional solutions and those projected by other well-known plate theories. Natural frequencies of the functionally graded plates with various side-to-thickness ratios, boundary conditions, and volume fraction index ‘n’ have been computed. It can be concluded that the proposed model is not only accurate but also simple in predicting the vibration behavior of functionally graded plates.

Commentary by Dr. Valentin Fuster
2016;():V001T03A011. doi:10.1115/IMECE2016-67885.

The dynamic buckling of a functionally graded material (FGM) circular plate subjected to thermal shock is studied in the Hamilton system. It is assumed that the lower surface of the circular plate is subjected to uniform thermal shock. Considering the one-dimensional heat conduction problem and basing on theory of Fourier heat conduction, the dynamic temperature fields of the FGM circular plate under thermal shock are obtained. The dynamic buckling problem of the FGM circular plate is finally reduced to zero-eigenvalue problem in the symplectic space. The critical loads and buckling modes of the functionally graded circular plate correspond to generalized eigenvalue and eigen solution, and can be obtained through bifurcation condition. In this study, the buckling characteristics of the FGM plate subjected to thermal shock are solved by symplectic method, and the solution process is given. The effects of the material constitution, structural geometric parameters and thermal shock load on the critical temperature are discussed.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Dynamic Behavior of Composites

2016;():V001T03A012. doi:10.1115/IMECE2016-65859.

The helicopter is an essential and unique means of transport nowadays and needs to hover in space for considerable amount of time. During hovering flight, the rotor blades continuously bend and twist causing an increased vibration level that affects the structural integrity of the rotor blade leading to ultimate blade failure. In order to predict the safe allowable vibration level of the helicopter rotor blade, it is important to properly estimate and monitor the vibration frequencies. Therefore, the mathematical model of a realistic helicopter rotor blade composed of composite material, is developed to estimate the characteristics of free and forced bending-torsion coupled vibration. The cross-sectional properties of the blade are calculated at first and are then included in the governing equations to solve the mathematical model. The natural frequencies and mode shapes of the composite helicopter rotor blade are evaluated for both the nonrotating and rotating cases. The time-varying bending and torsional deflections at the helicopter rotor blade tip are estimated with suitable initial conditions. The validation of the model is carried out by comparing the analytical frequencies with those obtained by the finite element model.

Commentary by Dr. Valentin Fuster
2016;():V001T03A013. doi:10.1115/IMECE2016-66252.

Liquid nanofoam (LN) as a novel material for energy absorption applications exhibits superior properties, including high energy absorption efficiency, ultra-fast energy dissipation, light weight and small size, over existing options. It is a liquid suspension of nanoporous particles, whose nanopore surface is non-wettable to the liquid molecules. Past studies on LN have focused on quasi-static responses, and the actual system performance under dynamic loadings has remained unclear. In this study, the mechanical behavior of two types of LN samples at various strain rates and the liquid flow speed in the nanopores have been experimentally investigated.

The quasi-static behavior of LN is rigorously characterized by an Instron 5982 universal tester, from which we find that large amount of energy is dissipated into heat due to the effective excess solid-liquid interfacial tension, and confirm that the energy absorption efficiency of the LN is determined by the liquid infiltration pressure and the total deformability.

The dynamic behavior of the LN is investigated by impacting it with a lab-customized drop tower apparatus at intermediate strain rates (around 102 s−1), from which the measured strain-stress curves are highly hysteretic. By comparing with the quasi-static sorption isotherm curve, we show that the liquid infiltration pressure as well as the total deformability of the LN sample in liquid marble form is not affected by the increased strain rate. This suggests that the dynamic behavior of LN can be characterized by quasi-static compressive tests.

In the dynamic tests, the ultra-fast energy dissipation rate of LN indicates that the real liquid flow speed in nanopores is much higher than that predicted by the continuum theory. The flow speed can be directly measured from the strain rate by considering the total surface area of the nanoporous particles exposed to the liquid phase. The flow speed is related to the external remote pressure and the 3D porous structure of nanoporous particles.

We have examined for the first time the dynamic behaviors of LN, and demonstrated the energy absorption capacity of LN can be activated at desired pressure range by virtue of the strain rate-independent liquid infiltration behavior. This is the first experimental approach to characterize the liquid flow speed in nano-environment. These findings provide strong evidence supporting the potential application of LNs to mitigate energy in blunt impact scenarios such as head to head and head to shoulder collisions in sports, traffic accidents and ballistic impact.

Commentary by Dr. Valentin Fuster
2016;():V001T03A014. doi:10.1115/IMECE2016-67664.

Textile composite are extensively used as structural materials for automotive, aerospace, energy, transportation and construction applications. During their service life these structures are subjected to different types of static and cyclic loading. For structural health monitoring of these structures, it is important to know the fatigue life and damage occurred at any stage of the life of the structure. Fatigue life is generally estimated using suitable life prediction model, while fatigue damage can be predicted by monitoring measurable damage parameters such as stiffness and strength. Two mathematical models namely fatigue life prediction model and stiffness degradation model are proposed for plain weave glass/epoxy composite subjected to flexural fatigue loading. Three different functions namely linear, exponential and sigmoid are evaluated to represent S-N diagram for plain weave glass/epoxy composite. Using predicted fatigue life along with initial modulus as inputs, the stiffness degradation model can predict residual stiffness at any stage of the fatigue loading life cycle. Logarithmic function used to represent stiffness degradation in the model is derived by inverting Boltzmann sigmoid function. The results of both, fatigue life model and stiffness degradation model were found to be in good agreement with those of the experimental results.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Dynamics and Control of Aerospace Structures

2016;():V001T03A015. doi:10.1115/IMECE2016-65303.

Biologically-inspired micro air vehicles (MAVs) are miniature-scaled autonomous aircrafts which attempt to biomimic the exceptional maneuver control during low-speed flight mastered by insects. Flexible wing structures are critical elements of a nature-inspired MAV as evidence supports that the wings of aerial insects experience highly-elastic deformations that enable insects to proficiently hover and maneuver in different airflow conditions. For this study, a crane fly (family Tipulidae) forewing is selected as the target specimen to replicate both its structural integrity and aerodynamic performance. The artificial insect-sized wing is manufactured using photolithography with negative photoresist SU-8 to fabricate the vein geometry. A Kapton film is attached to the vein pattern for the assembling of the wing. The natural frequencies and mode shapes of the artificial wing are determined to characterize its vibrations. A numerical simulation of the fluid-structure interaction is conducted by coupling a finite element model of the artificial wing with a computational fluid dynamics model of the surrounding airflow. From these simulations, the deformation response and the coefficients of drag and lift of the artificial wing are predicted for different freestream velocities and angles of attack. The deformation along the span of the wing increases nonlinearly with Reynolds number from the root to the tip of the wing. The coefficient of lift increases with angle of attack and Reynolds number. The coefficient of drag decreases with Reynolds number and angle of attack. The aerodynamic efficiency, defined as the ratio of the coefficient of lift to the coefficient of drag, of the artificial wing increases with angle of attack and Reynolds number.

Topics: Vehicles , Biomimetics , Wings
Commentary by Dr. Valentin Fuster
2016;():V001T03A016. doi:10.1115/IMECE2016-65854.

The powder-bed electron beam additive manufacturing (EBAM) process is one of the relatively new additive manufacturing (AM) technologies in which the metal powder is melted in a vacuum environment utilizing a high-energy heat source to fabricate metallic parts in a layer by layer manner. Different metallic alloys (especially, high entropy alloys such as Ti-6Al-4V) have been widely studied as a powder-bed material for the EBAM. Despite the unique advantages of designing complex geometry and tooling-free manufacturing, there are still considerable challenges in the EBAM, e.g., obtaining desired metallurgical behavior, part accuracy, reliability, and quality consistency. Therefore, a better understanding of the thermo-fluid and mechanical properties of the EBAM process is indispensable to meet the challenges. In this study, transient computational fluid dynamics (CFD) modeling of Ti-6Al-4V melt pool has been done using ANSYS Fluent 15.0 to characterize the process parameters associated with the EBAM process including the melt pool geometry, beam power, beam speed, beam diameter, and temperature profile along the melt scan. In fact, the dynamics and the solidification of the melt pool have been investigated numerically and results for cooling rate, variation in density, pressure, velocities, and liquid fraction have been obtained to illustrate the versatility of the analysis.

Commentary by Dr. Valentin Fuster
2016;():V001T03A017. doi:10.1115/IMECE2016-67043.

To achieve greater efficiency with lightweighting, new configurations are being explored in aero engine design. Typically, these configurations include large flexible structures such as fan blades which require adequate modeling techniques to capture their dynamic effects accurately. For the analyses of these components, the traditional one-dimensional Rotordynamics modeling approach is not sufficient and even two-dimensional axisymmetric harmonic elements cannot capture discrete rotor blades and their complex non-uniform geometries. These limitations motivate the use of three-dimensional (3D) solid/shell elements. They allow for a geometrically complete representation of the rotor as well as analysis in both the fixed and the rotating reference frames. The advantages of 3D elements for rotordynamic analyses are demonstrated using a turbofan engine model. The results reveal the effect of dynamic coupling between the fan blades and the rotor shaft on rotor deformation due to unbalance loads.

Commentary by Dr. Valentin Fuster
2016;():V001T03A018. doi:10.1115/IMECE2016-67416.

Many insights can still be gained from the flapping flight of nature’s flyers, particularly from how they can effortlessly transition between flight modes and maneuver in obstacle-strewn environments. Furthermore, they are able to do this without the typical control surfaces found in manmade vehicles. Many theories have been postulated on how this is accomplished and they often involve control of individual wing position and stroke velocity. As such, direct sensing of wing motion both in flapping and in rotation would be desirable. In this work, we look at implementing wing motion sensing through the use of optical sensors. We develop sensing designs for both the transmissive and reflective sensor types, present design reasoning, and discuss the advantages and disadvantages of their use. Finally, we employ the sensors on the wing of a flapping wing MAV capable of power autonomous flight and demonstrate successful sensor tracking of general wing motion.

Topics: Rotation , Vehicles , Wings
Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: General

2016;():V001T03A019. doi:10.1115/IMECE2016-65312.

The stacking sequence of composite laminates is designed to have maximum buckling load using the particle swarm optimization (PSO) algorithm. The original PSO algorithm is modified to handle the discrete ply angles and the constraints such as stiffness and 4-ply contiguity requirements. For this, the augmented Lagrange multiplier (ALM) method is incorporated into the PSO algorithm. For the verification of the algorithm, the benchmarking problems are solved and the results are compared with the ones from the genetic algorithm or the analytic solutions. And then the laminates under in-plane compressive loadings are optimized for maximum buckling load considering the various constraints. The numerical results show that the algorithm finds the optimum with relatively small number of iterations with satisfying the constraints explicitly. Considering its advantage of derivative-free and simple procedures, the proposed algorithm can be applied to more complex models coupled with finite element analysis and various constraints.

Commentary by Dr. Valentin Fuster
2016;():V001T03A020. doi:10.1115/IMECE2016-65586.

Steam turbine rotors are subjected to various excitation forces originated from inner structure and outer environment. Unbalance forces, nonlinear oil film forces, nonlinear seal forces, and base excitation are drastically influence the dynamic behaviors of the rotor system. A mathematical model of rotor system, including the coupled effects of these excitation forces, is established by applying the Lagrange’s equations. The axial flow velocity and leakage mass flow, which vary with the structure of labyrinth seal and with inlet/outlet pressure ratio, are calculated using the two-control-volume model. The axial mean flow velocity is then introduced into the Muszynska’s nonlinear seal forces model. The nonlinear oil-film forces are also obtained based on the short bearing theory. The equations of motion are solved by Runge-Kutta numerical integration. The influences of inlet pressure and seal strip number on axial mean flow velocity and leakage mass flow are analyzed. The effects of rotational speed, foundation movements and inlet pressure on the nonlinear dynamic characteristics of the labyrinth seal-bearing-rotor system are investigated. The bifurcation diagrams, axis orbits and spectrum cascades are used to analyze the nonlinear dynamic behaviors of the system.

Commentary by Dr. Valentin Fuster
2016;():V001T03A021. doi:10.1115/IMECE2016-65807.

The acquirement of lunar soil samples is the foundation to analyze and know about the composition of lunar soil and the lunar geologic structure. Because of the restrictions of the sampling method, the size of driller, the drilling pressure and the driller’s output power, the traditional digging method and vertical drilling method can only acquire the samples from lunar surface to 3 meters deep. In order to acquire the deeper samples based on the existing technique methods, a new exploration concept in which a driller fixed on the rover takes a horizontal drilling and sampling at the cross section of a crater after cleaning the surface chaotic soil was proposed in this paper. When drilling horizontally, the maximum drilling pressure is limited by the low adhesive ability between wheels and soil. For the purpose of making sure enough drilling pressure, study was carried out in this paper to improve the wheel’s adhesive ability by modifying the wheel’s surface. A wheel with a new kind of micro convex structures was proved to be more adhesive and stable during horizontal drilling by comparing with the existing wheel structures, such as wheel with thorns or discontinuous rims. The structural parameters of the convex structures may have significant influences on the adhesive ability. In order to study the effects of the convex structure’s parameters on wheel’s adhesive ability, the motion process of wheels on sandy road was simulated by using a DEM software EDEM. According to the simulation results, when the structural parameters of the convex structures are: flat-end shape, length/diameter = 5 and distribution density = 81/mm2, the wheel’s adhesive ability is much better than the wheel with other parameters based on a criterion which is the ratio of the tangential force to the normal force in the tangential motion process. Besides, the friction coefficient of wheels with convex structures is about 5 times as much as the friction coefficient of normal wheels, which proves that it is a useful method to improve wheel’s adhesive ability by modifying wheel’s surface with the convex structures.

Commentary by Dr. Valentin Fuster
2016;():V001T03A022. doi:10.1115/IMECE2016-65816.

For the on-orbit servicing missions of spacecraft, space robot is considered as one of the most promising approaches. Many on-orbit servicing missions are successfully accomplished and most of these missions are designed to service cooperative targets only. Some of the target is non-cooperative spacecraft with unknown motion and kinematics properties. On-orbit servicing is still a challenging research area. The challenge is to ensure the servicing spacecraft safely and stabilize it for subsequent servicing. In order to expand space robot workspace and its task function, this paper presents a new type of space climbing robot which can be carried on mechanical arm. It can climb onto the target spacecraft for repairing, rescuing and removing orbital debris when the connection is established between the space manipulator and the target spacecraft. This robot mobile system is composed of piezoelectric actuation leg, micro adhesive feet, ejector and manipulator. The robot’s crotch joint and ankle joint both have two degrees of freedom with Roll-Pitch organization. In the environment of zero-gravity the obstacles on the target can be crossed by space climbing robot through wriggle movement and turnover movement. The gripping force of the robot is supplied by the adhesive capacity of the robot feet while robot climb along the surface of target spacecraft with weightlessness. The research of its adhesion mechanism is the basis of robot feet design and motion control. The design of robot feet micro array structure imitates the adhesion mechanism of gecko seta. A contact model between the robot feet and spacecraft surface is proposed. A single seta’s DEM (Discrete Element Method) model is set up by stacking micro particles, on the software platform of EDEM. EDEM is a software for discrete element analysis. The attachment and the detachment process of a single seta in different slope angle and its adhesion properties are simulated by using JKR model which is a classical contact mechanics model. The simulation demonstrate that the single seta’s gripping force with 90 degree slope angle is about 20% of the gripping force with 30 degree slope angle. The fiber structure was destroyed by large pressure making failure to its adhesion properties when the slope angle is zero. So the different ways of movement can achieve different adhesion properties of single seta. When the movement of micro array structure is determined, in order to improve the robust adhesion properties, well stability and excellent adaptability of the micro array structure, the structure parameters of seta is optimized. The structure parameters include the cylinder radius, length-diameter ratio and arrangement density of the micro array structure. A group of micro array structure optimized parameters is given according to the DEM comparing simulations with different structure parameters. This work propose a novel adhesion concept for climbing robot in space environment, and the stable attaching and easy detaching mechanism of the robot is also given.

Topics: Adhesion , Robots
Commentary by Dr. Valentin Fuster
2016;():V001T03A023. doi:10.1115/IMECE2016-66356.

The liquid lubrication is one of the most common lubrication modes in long-term space equipment, the sealing for liquid lubricants is thus important. Woven brush seal is motived by contact, which is able to achieve zero gap and thus have better performance than others. In this paper, we propose a woven brush seal system based on the model of porous medium with deformation of woven brush wire in anisotropic. For estimating the leakage and verifying availability of our system, we build calculation models by employing finite volume k-epsilon model and SIMPSON calculation method. Additionally, we run both simulation and experiments to evaluate our system, the calculation and experimental results show that: the leakage is much lower than traditional labyrinth seal, the amount of leakage increases gradually with the increase of rotational speed. The calculation method and boundary conditions are consistent with the actual situation. Namely, woven brush is able to satisfy the requirements in vacuum environment and thus considered as the corresponding seal component.

Topics: Vacuum , Simulation , Testing
Commentary by Dr. Valentin Fuster
2016;():V001T03A024. doi:10.1115/IMECE2016-66381.

Nowadays, there are more works focused on the design and implementation of space mechanics under harsh environmental conditions, such as absence of a gravitational field. Precisely, the reliability and life of space mechanical components is still not adequate. Therefore, the deep-space exploration brings a challenge on lubrication system of space equipment. Centrifugal lubricators, oozing flow lubricators, wick feed systems and porous lubricant reservoirs are most common liquid lubrication systems used in space devices. But the oil amount is not sufficient. Additionally, it is needed to develop efficient supplementary lubrication systems to achieve future long-term space missions since the lacking of oil. In this paper, we propose liquid lubricating bearing system with built-in oil storage chamber for conquering lacking of oil. We also build the theoretical models for through vibration displacement and frequency of rolling element, bending deformation and vibration frequency of the elastomeric shaft, and the radiation energy of chamber’s inner surface respectively. These models are evaluated by numerical simulations. We tested and measured some parameters of oil flowing in system. The simulation and experimental results indicate that, 1) the rolling element has a through vibration displacement when bearing running; 2) the micro deformation and vibration of the elastomeric shaft are caused by the through vibration displacement; 3) the vibration energy of elastomeric shaft is transmitted to lubricating oil stored in chamber. Overall, the oil could be supplied to bearing race and friction surface through connecting oil hole drilled in the elastomeric shaft. The oil flowing performance varies with the diameter and inclination angle of the connecting oil hole.

Commentary by Dr. Valentin Fuster
2016;():V001T03A025. doi:10.1115/IMECE2016-66399.

The simulation of unsteady turbulent flows remains a significant problem in CFD despite the tremendous advances in the performance of supercomputers during the past decades. Considering this state, the enhancement of the in-house academic CFD solver Galatea-I with the LES approach is reported in this study. LES is actually a compromise between the RANS and DNS methods, entailing though increased accuracy, comparing to the first one, and less computational load than the second. Particularly, four Sub-Grid Scale models have been incorporated, namely, the Smagorinsky, the WALE, the dynamic Germano-Lilly and the dynamic kinetic energy one. They were validated against a real 3D problem, concerning turbulent flow over the CAARC standard tall building model, a specially designed geometry for wind tunnel experiments on tall buildings. Independently of the implemented modelling approach, the extracted results appear to be close with the available experimental and numerically computed data, confirming the potential of Galatea-I to encounter such simulations. The last two models are revealed to be the most accurate ones, a conclusion actually expected due to their more sophisticated formulation. An additional simulation was performed with the RANS approach and the SST model, which confirmed the superiority of the LES methodology in terms of accuracy.

Commentary by Dr. Valentin Fuster
2016;():V001T03A026. doi:10.1115/IMECE2016-66412.

The development of an efficient partitioned FSI coupling scheme is reported in this paper, aimed to facilitate interaction between an open-source CSD software package and an in-house academic CFD code. The coupling procedure is based on Radial Basis Functions (RBFs) interpolation for both information transfer and mesh deformation, entailing no dependence on connectivities, and hence making it applicable to different type or even intersecting grids. However, the method calls for increased computational resources in its initial formulation; to alleviate this deficiency, appropriate acceleration techniques have been incorporated, namely the Partition of Unity (PoU) approach and a surface-point reduction scheme. The PoU approach was adopted in case of data transfer, localizing the interpolation process and therefore reducing the size of the coupling matrix. An alternative approach was applied to improve the efficiency of the mesh deformation procedure, based on the agglomeration of the flow/structure interface nodes used for the RBFs interpolation method. For the demonstration of the proposed scheme a static aeroelastic simulation of a real bridge model, during its construction phase, was performed. The extracted results exhibit its potential to encounter effectively such complicated test cases, in a computationally efficient way.

Commentary by Dr. Valentin Fuster
2016;():V001T03A027. doi:10.1115/IMECE2016-66703.

In this study, three dimensional flow analysis of one and a half stage axial turbine is investigated. The objective of this study is to analyse the effect of rotor stator interaction and the resulting unsteadiness. This includes the effect of first row of Nozzle guide vane (NGV) wakes on rotor blades, secondary vortical flow prediction, influence of rotor wakes on the flow pattern of second stator, appreciation and application of techniques to model the exact blade counts across the rotor-stator interfaces. We employ a three-dimensional finite-volume based solver to simulate the flow in the turbine using SST model to account for turbulence effects. Sliding mesh technique is used to allow the transfer of flow parameters across the sliding rotor/stator interfaces. In order to model a single passage configuration, profile transformation and time transformation method is used. The flow physics for the visualization and understanding of flow behavior in a 3D turbine cascade is explained in detail and validated with the previous experimental and numerical studies. The study provides application of computationally efficient methods for simulating the fluid flow in a turbine which contain unequal number of rotor and stator blades.

Commentary by Dr. Valentin Fuster
2016;():V001T03A028. doi:10.1115/IMECE2016-67930.

The airfoil/wing design is probably the most important part of an aircraft design. A practical aerodynamic design of airfoil requires optimal performance on a wide range of operating conditions. These requirements are often found to be conflicting and demand designer expertise for satisfactory results, not to mention the computational burden of the simulations. Although there exists many studies on direct and inverse design of airfoils, less attention has been paid to simultaneous consideration of multiple objectives. In this paper, a multi-objective optimal airfoil design procedure is presented. PARSEC parametrization method has been utilized to express the airfoil geometry in terms of twelve physical parameters. The aerodynamic performance is obtained by 2D panel method using XFOIL package. Multi-Objective Particle Swarm Optimization (MOPSO) algorithm has been applied for airfoil geometry design because it is efficient and keeps the diversity among the solution set. The objective functions and constraints are chosen to enhance the flight performance at takeoff, cruise, and landing conditions for a long range cargo aircraft. Objectives include maximization of lift to drag ratio (CL/CD), maximization of rate of change of lift to attack angle (dCL/dα) for having increased lift at takeoff/landing condition and minimization of pitching moment Display FormulaCM2. Two applied constraints are CL > CLmin at operating condition and thickness ≤ %25. Each evaluation is consist of finding the optimal operating angle of attack and reporting the corresponding objective values. The quality of the solution at various generations has been studied to guarantee the convergence of the solution. Like any other multi-objective optimization problem (MOP), the solution would be a set of Pareto optimal configurations. Although having multiple solutions gives us a better understanding of the problem, only one configuration should be chosen by the designer. A post processing technique is also used to help the decision maker to choose the most appropriate compromise in the solution set. The method is found to be effective in finding efficient set of airfoils. The simulation is also found to be effective because it can be done on a regular personal computer. It should be noticed that the method can be easily applied to other airfoil design applications by simply modifying the objective functions and the constraints.

Topics: Design , Aircraft , Airfoils
Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: High Temperature Materials and Structures

2016;():V001T03A029. doi:10.1115/IMECE2016-65389.

Due to the harsh environments created by high speeds, significant new demands are placed on materials used for constructing hypersonic vehicles. Ultra high temperature ceramics (UHTCs) like carbides and borides exhibit unique thermal properties, such as very high melting points and good thermal conductivities. These properties make the ceramic materials good candidates for applications like Thermal Protection Systems (TPS) of the hypersonic vehicles. However, thermal properties of UHTCs may be very sensitive to microstructures of the materials. Thus, atomic scale defects may impact certain thermal properties, such as thermal conductivity. The effects of such small defects may be properly studied only through atomistic simulation methods, such as molecular dynamics (MD). Previously, atomistic simulation studies have been performed for the effects of point defects on thermal properties in silicon carbide (SiC). In addition, atomistic simulations have been applied to assess thermal conductivity in zirconium diboride (ZrB2) for perfect crystals and polycrystals. However, to our knowledge, no studies of the effects of point defects have been performed for zirconium diboride. This paper applies atomistic simulations to assess the impact of point defects on thermal conductivity in ZrB2 perfect crystals. Recently derived interatomic potential for ZrB2 along with LAMMPS molecular simulation package and MedeA software environment are employed in this effort. Phonon part of the thermal conductivity is calculated using Green-Kubo method. Calculations for a perfect crystal are conducted first and the results are compared to experimental data available from the literature. Then, several types of point defects are considered (vacancies, substitutions, and interstitials) and their impact on the phonon conductivity is evaluated. It is found that even a small concentration of point defects may have substantial effect and result in a reduction in the thermal conductivity values by almost an order of magnitude. The obtained results are in good qualitative agreement with previous studies conducted for silicon carbide. The methodology which is utilized in this work, the modeling procedure, and the obtained results are discussed in this paper.

Commentary by Dr. Valentin Fuster
2016;():V001T03A030. doi:10.1115/IMECE2016-65728.

In this work, the influence of lightning-strike-induced electric current and surface heat flux on the thermal response and thermal ablation of a carbon fiber polymer matrix composite laminated panel is studied. A coupled electric-thermal model for an anisotropic plate exposed to the lightning-strike-induced electric current and surface heat flux is formulated. Temperature-dependent material properties of the carbon fiber polymer matrix composites, including electrical conductivity, thermal conductivity, and specific heat, are used. A coupled electric-thermal finite element analysis (FEA) is conducted using a MATLAB-ABAQUS integrated numerical procedure, which enables progressive element deletion to accurately model the lightning-strike-induced continuous surface recession (thermal ablation) in the composite panel. The obtained thermal response and thermal ablation using the proposed numerical procedure are compared with those obtained using existing solution procedures without progressive element deletion.

Commentary by Dr. Valentin Fuster
2016;():V001T03A031. doi:10.1115/IMECE2016-65763.

Airframe structures and components on many existing and future Air Force aerospace systems require operation in elevated temperature. Examples include hypersonic vehicle airframes, engine related components (such as engine ducts, engine vanes, and exhaust flaps), and hot trailing edges of B-2 and C-17 wings. Material systems that show improved fatigue performance, excellent thermal resistance, and damage tolerance are prime candidate materials for potential air vehicle structural components. Polymer matrix composites (PMCs) and ceramic matrix composites (CMCs) are two types of composites used in aircraft structures subjected to high temperatures. The polymer matrix in most PMCs cannot withstand the temperatures required for many aerospace structural applications. Therefore, either improvements in temperature capability of polymer matrix materials or developing novel thermal protection systems are desired for elevated temperature applications. Any new material system intended for aerospace applications must be studied and tested to verify that the mechanical properties are sufficient for use in the operating environments. This study investigated the mechanical properties and tension-tension fatigue behavior of two newly developed material systems for use in structures subjected to elevated temperatures, namely a 2D weave PMC and a 2D weave unitized composite (or PMC/CMC, consisting of a PMC co-cured with a CMC layer to act as a thermal barrier). These two material systems are two of three new composites developed under contract through the Air Force Research Laboratory (AFRL) and investigated during a master’s thesis research program at the Air Force Institute of Technology (AFIT) [1].

The 2D PMC investigated in this effort consisted of an NRPE (a high-temperature polyimide) matrix reinforced with carbon fibers. The fiber architecture of the PMC was an 8 harness satin weave fiber fabric. The PMC portion of the unitized composite had the same constituent properties and weave as the aforementioned 2D PMC. The CMC layer consisted of a zirconia-based matrix reinforced with an 8 harness satin weave quartz fiber fabric. For both material systems (PMC and PMC/CMC), material properties were investigated for both on-axis [0°/90°] and off-axis [±45°] fiber orientations. Tensile properties were evaluated at (1) room temperature and (2) with one side of the specimen at 329 °C and the other side exposed to ambient air. Tension-tension fatigue tests were conducted at elevated temperature at a frequency of 1.0 Hz with a ratio of minimum stress to maximum stress of R = 0.05. Fatigue run-out for this effort was defined as 2×105 cycles. Elevated temperature had little effect on the tensile properties of both material systems with the 0°/90° fiber orientation; however, specimens with the ±45° fiber orientation exhibited a significant increase in failure strain at elevated temperature. The ultimate tensile strength (UTS) of the 2D PMC with the ±45° fiber orientation decreased slightly at elevated temperature, but the UTS of the unitized composite with ±45° fiber orientation showed no significant change. The unitized composite did not exhibit an increase in tensile strength and stiffness compared to the 2D PMC. However, the 2D PMC with ±45° fiber orientation produced significantly greater failure strain. The 2D PMC showed slightly better fatigue resistance than the unitized composite with the 0°/90° fiber orientation. For the ±45° fiber orientation, the fatigue limit for the 2D PMC was approximately two times greater than that for the unitized composite. Microstructural investigation of tested specimens revealed delamination in the 2D PMC and very severe delamination in the unitized composite.

Commentary by Dr. Valentin Fuster
2016;():V001T03A032. doi:10.1115/IMECE2016-66774.

One of the major concerns in long duration space exploration is to minimize the exposure of crew and equipment to space radiation. High energy radiation not only can be hazardous to the health but also can damage the materials and electronics. Current designs are contained heavy metals to avoid occupational hazards from radiation exposures. As a result the shielding structures are heavy and not effective to attenuate all types of radiation. Therefore, the proposed lightweight sandwich composites are designed to effectively shield high energy radiations while providing structural integrity. In the manufactured hybrid sandwich composite, High Molecular Weight Poly Ethylene (HMWPE) woven fabrics are selected as face sheets due to their advanced mechanical properties and excellent physical properties along with effective shielding properties. Basically polymers due to high hydrogen content are considered as effective materials to attenuate high energy radiations. In addition, the core material is epoxy composites incorporating three weight percentages of three different nanoparticles viz. Boron Carbide, Boron Nanopowder and Gadolinium. In fact if polymers as low Z materials are used alone, they usually are not successful to attenuate highly penetrative rays. Therefore, one solution is known to infuse polymer matrix with high radiation absorption properties nanoparticles. Among several different nanomaterials, the three aforementioned nanofillers were chosen because of their good radiation absorption properties. Gadolinium has the highest thermal neutron cross section compare to any other known element and 10B-containing materials are known as excellent radiation absorbers and the composite filled with them have the advantage of convenient and safety in construction, operation and reintegration. The sandwich composites were manufactured using Heat-Vacuum Assisted Resin Transfer Molding method (H-VARTM), which is a cost effective method for high volume production of sandwich structures. To evaluate the shielding performance of manufactured sandwich panels the neutron attenuation testing was performed. The results from neutron radiation tests show more than 99% shielding performance in all of the sandwich panels. In comparison with other nanofillers, Boron Nanopowder showed highest radiation shielding efficiency (99.64%), which can be attributed to its lowest particle size and better dispersion ability into epoxy resin. The flatwise compression testing was performed on all four sandwich panels to determine the mechanical strength of materials before and after being exposure to radiation. The results demonstrate that proposed hybrid sandwich panels can preserve their mechanical integrity while being exposed to the radiation.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Impact, Damage and Fracture of Composite Structures

2016;():V001T03A033. doi:10.1115/IMECE2016-65682.

The matrix compression parameters in continuum damage mechanics models are often calculated from assumptions requiring detailed knowledge of fracture and frictional behavior of the material. A direct method for experimentally determining the matrix compression damage parameters would simplify the process and potentially increase accuracy of parameters. In this study, specimen geometry is determined and validated to directly evaluate the energy dissipated by matrix compression damage experimentally. Initially, candidate specimens were determined from literature on fiber compression testing including compact compression (CC), center notched compression (CNC), and four-point bending (4PB) specimens. These specimens were modeled using the finite element program ABAQUS. Geometry and boundary conditions of the specimens were varied to test different specimen geometries and fixture types. The matrix compression damage isolation of the specimens was evaluated by measuring the region of matrix compression damage without other damage modes present in the material. 4PB specimens showed damage primarily at the loading points. Both CNC and CC specimens showed fairly good isolation of matrix compression damage with the former showing a tendency to split off-axis depending on the fixture used and the latter showing tensile splitting after significant compressive damage growth. CC specimens were selected because they require less complex loading fixtures and are less dependent on the fixtures for damage isolation than CNC specimens. The geometry was varied on the CC specimens to increase the compression damage isolation. Specimens were manufactured for experimental validation. A layup with the fiber direction of all plies parallel to the notch tip was used to isolate the loading to the matrix. It was determined that 20 plies was sufficiently thick to prevent bucking. The specimens showed good isolation of compression damage at the notch tip. This is due to the stress concentration at the notch tip that lowers the load required to cause compression damage to below the global buckling load. Ultimate failure was due to tensile splitting opposite of the notch, but only after sufficient compressive damage growth. The size of the damage zone was able to be tracked visually from video of the tests. Load-displacement data and the damage zone size were used to calculate the strain energy release rate using the basic compliance calibration method. This method is limited because it is based in fracture mechanics principals and may not be accurate for the damage modes present in the material, but is sufficient for initial validation of the CC specimen. The strain energy release rate for the material was measured to be 35 in-lbs./in2. CC specimens show promise for measuring the energy dissipation of matrix compression damage for use in continuum damage mechanics models due to their ability to isolate compressive damage modes without buckling. Refined data collection methods can be implemented to increase the accuracy and generality of the strain energy release rate measured.

Commentary by Dr. Valentin Fuster
2016;():V001T03A034. doi:10.1115/IMECE2016-67342.

Recently, the development of hydrophobic nanoporous liquids has drawn increased attention, especially for the applications of energy absorption and impact protection. Although significant amount of research has been conducted to synthesis and characterize materials to protect structures from impact damage, the tradition methods needed to convert kinetic energy to other forms, such as heat and cell bulking, during impact protection. Due to their high energy absorption efficiency, hydrophobic nanoporous particle liquids are one of the most attractive impact mitigation materials. When impacted, such particles directly trap liquid molecules inside the non-wetting surface of nanopores in the particles. The captured impact energy is simply stored temporarily and isolated from the original energy transmission path.

In this paper we investigate the energy absorption efficiency of multiple nanoporous particles and liquids. Inorganic nanoporous silica nanoparticles are investigated as the hydrophobic materials. Nanoporous particle liquids are prepared by dispersing the nano-materials in deionized water. The effects of small molecular promoters, such as methanol and ethanol, on energy absorption efficiency, are studied in this paper. The energy absorption efficiency of these liquids is experimentally characterized using an Instron mechanical testing frame and in-house develop stainless steel hydraulic cylinder system under quasi-static load conditions.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Lightweight Sandwich Composites and Layered Structures

2016;():V001T03A035. doi:10.1115/IMECE2016-66294.

Sea water and cold temperatures appear to have an adverse effect on naval materials resulting in the degradation of their mechanical properties. In this paper, the effects of sea water absorption and arctic conditioning have on the mechanical properties of divinycell foams are discussed. For this study, moisture absorption was periodically measured until weight gain equilibrium or saturation was reached for samples submerged in sea water and deionized water. Diffusivities and saturation values were obtained from moisture uptake curves. It was observed that the moisture content was higher for the vinyl foam samples submerged in deionized water compared to the samples submerged in synthetic sea water. Diffusivities were 9.227E-06 Display Formulamm2sec and 1.390E-05 Display Formulamm2sec for deionized water and sea water conditioning, respectively. Flexural and compression tests were then conducted on conditioned samples to compare their response against non-exposed samples. Experimental findings showed degradation in the flexural modulus and the compressive modulus for saturated wet samples and arctic-dry samples. This occurrence can be observed in both tests with more prominent reduction in its flexural modulus for arctic-dry samples and in compression for submerged in deionized water samples. Such a reduction is attributed to the degradation caused by the water, both deionized water and sea water, in the form of surface damage to specimens.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Multiscale Models and Experimental Techniques for Composite Materials and Structures

2016;():V001T03A036. doi:10.1115/IMECE2016-65447.

In this paper a multiscale-modeling framework is presented wherein fundamental damage information at the atomic level is coupled with a sectional micromechanics model for the nonlinear and damage analysis of carbon fiber reinforced polymer (CFRP) composites. Damage information in the polymer matrix originating from the atomic scale, as investigated using molecular dynamics (MD) simulations, is transferred to the continuum length scale using a continuum damage mechanics approach with a physical damage evolution equation. Such a framework is shown to be computationally efficient for the linear and damage analysis of CFRP composites and reasonably accurate when compared to experimental data and verified models in literature. Furthermore, material uncertainty, such as curing degree variation in polymers, can be computationally calculated leading to a computational stochastic analysis of the CFRP composites. Thus, such a framework can be used to investigate the damage mechanics of ply level CFRP components at the nano, micro and macro length scales.

Commentary by Dr. Valentin Fuster
2016;():V001T03A037. doi:10.1115/IMECE2016-66907.

Tests were carried out to determine the interlaminar fracture toughness of stitch-bonded biaxial polymer matrix carbon nanotube nanocomposites for mode I, II, and I-II including durability effects. Analysis of the test specimens in terms of mode I energy release rates showed good agreement among Modified Beam Theory, Compliance Calibration, and Modified Compliance Calibration methods. End-Notched Flexure (ENF) and four point End-Notched Flexure (4ENF) tests gave very consistent crack initiation and propagation results for mode II fracture. The results show that the critical mode I energy release rate for delamination decreases monotonically with increasing mode II loading. The effects of accelerated aging (60°C and 90% Rh) on fracture properties were studied. Early accelerated aging (0–12 months) has the dominant diminishing effect on energy release rate initiation and propagation in composites and nanocomposites.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Next Generation Aerospace Technologies

2016;():V001T03A038. doi:10.1115/IMECE2016-65683.

This paper describes the test methodology and results for a wind tunnel experiment featuring a blended wing aircraft in ground effect with built-in circulation control. A 82.55cm wingspan blended wing model was tested in a subsonic wind tunnel at velocities ranging from 18m/s – 49m/s and corresponding Reynolds numbers ranging from 130k – 350k. Pitch angle was held constant at 0 degrees and the height above the wind tunnel floor was modified to determine lift and drag modification due to ground effect. At a normalized height (y/bw) of 0.06, ground effect increased lift production by 24% and reduced drag by 22% when compared to a normalized height of 0.5. The addition of the circulation control significantly increased the lift production of the model at a cost of increased drag. At a normalized height of 0.031, the lift production increased by 200% at a blowing coefficient of 0.01, but the drag also increased by 72%, ultimately increasing L/D by 178%. Experimental results also suggest that ground effect and circulation control have a synergistic effect when used simultaneously. The effects of Reynolds number and circulation control slot height are also investigated.

Commentary by Dr. Valentin Fuster
2016;():V001T03A039. doi:10.1115/IMECE2016-65846.

Regular, routine and affordable access to low Earth orbit (LEO) with heavy payloads is essential to develop infrastructure beyond Earth. A Space Solar Power system based on the Intensified Conversion architecture gives the market parameters to routinely transfer 25000 kg to and from LEO. An initial analysis combines aerodynamics and aerothermodynamics. A hydrogen-oxygen system which collects the oxygen for the rocket phase in flight. The transonic airliner class carrier with hydrogen-fueled turbofans contains the equipment for oxygen collection during subsonic ascent. The second stage starts as transonic ramjet near 18000m, transitions to supersonic combustion at Mach 5 and then to rocket. Aerodynamic lifting surfaces sized by the second stage landing are used in supersonic ascent. This establishes a new basis to estimate launch cost for large-scale infrastructure development in orbit. The optimization results show that a supersonic carrier to Mach 2 and above, along with a higher release altitude for the second stage, should improve payload, but requires design of a completely new supersonic carrier. The results also show the need for oxygen liquefaction systems optimized for LACE and utilizing the availability of liquid hydrogen at the rate needed by the engines.

Topics: Optimization , Cycles
Commentary by Dr. Valentin Fuster
2016;():V001T03A040. doi:10.1115/IMECE2016-66436.

In the field of more electric aircraft, electromechanical actuators (EMAs) are becoming more and more attractive because of their outstanding benefits of aircraft fuel reduction, maintenance costs saving, and system flexibility improvement. For aerospace electromechanical actuator applications, mechanical power transmission is critical for safety, in which reflected inertia to load, heat generated by energy losses and faults due to jamming, free-play and free-run are specific issues. According to the system-engineering process and simulation-aided design, this communication proposes an incremental approach for the virtual prototyping of EMA mechanical power transmission. Resorting to the Bond-graph formalism, the parasitic effects are progressively introduced and realism of models is increased step-by-step. Finally, the numerical implementations are presented and compared with basic, advanced and full models of mechanical power transmission in AMESim environment. Multi-level submodels are available and can be re-used for preliminary sizing, thermal balance verification and response to fault analysis.

Commentary by Dr. Valentin Fuster
2016;():V001T03A041. doi:10.1115/IMECE2016-66650.

Germanys fifth Aeronautical Research Program (LuFo-V) gives the framework for the TERA-project (Thermoelectric Energy Recuperation for Aviation), which focuses on the positioning of thermoelectricity by means of a holistic reflection of technological possibilities and challenges for the adoption of thermoelectric generators (TEG) to aircraft systems. The aim of this paper is to show the project overview and some first estimations of the performance of an integrated TEG between the hot section of an engine and the cooler bypass flow. Therefore, casing integration positions close to different components are considered such as high pressure turbine, low pressure turbine, nozzle or one of the interducts, where temperature gradients are high enough for efficient TEG function. TEG efficiency is then to be optimized by taking into account occurring thermal resistance, heat transfer mechanisms, efficiency factors, as well as installation and operational system constrains like weight and space.

Topics: Aviation
Commentary by Dr. Valentin Fuster
2016;():V001T03A042. doi:10.1115/IMECE2016-67745.

The following work is presented as a preliminary study on the effects of gamma irradiation on mechanical properties of Acrylonitrile Butadiene Styrene (ABS) as an in-space 3D printing feedstock to investigate the forthcoming possibilities of this technology for future space exploration missions. 3D printed testing samples were irradiated at different dosages from 1 to 1400 kGy (1 Gray (Gy) = 1 J/kg = 100 rad) using a Cobalt-60 gamma irradiator to simulate space radiation environment. Testing samples were manufactured using Fused Deposition Modeling (FDM) with a Makerbot Replicator 2x 3D printer. The correlation between the mechanical properties of irradiated samples and accumulated radiation dosage were evaluated by a series of tensile and flexural tests. Furthermore, Shore hardness tests were conducted to evaluate changes in surface hardness of irradiated parts. Finally, results were compared with a control group of samples. Findings showed a significant decrease in mechanical performance and noticeable changes in appearance of the parts with accumulated dosage of 1000 kGy and higher. However, for dosages below 10 kGy, samples showed no significant decrease in mechanical performance or change in appearance. These results were used to predict the life of a 3D printed part on board the International Space Station (ISS), on Low Earth Orbit (LEO) satellites, in deep space and long duration missions.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Peridynamics Modeling

2016;():V001T03A043. doi:10.1115/IMECE2016-65340.

In this paper we introduce a simple and efficient approach to couple a discretized Peridynamic model with a meshless method based on classical continuum mechanics. The coupling is done through a complete meshless style without producing any ghost forces in the transition region. We shall show with such type of coupling it is possible to reproduce the solution of a pure Peridynamic model by a hybrid meshless method with lower computational cost.

Commentary by Dr. Valentin Fuster
2016;():V001T03A044. doi:10.1115/IMECE2016-65841.

In contrast to the classical local and nonlocal theories, the peridynamic equation of motion introduced by Silling (J. Mech. Phys. Solids 2000; 48: 175–209) is free of any spatial derivatives of displacement. The new general integral equations (GIE) connecting the displacement fields in the point being considered and the surrounding points of random structure composite materials (CMs) is proposed. For statistically homogeneous thermoperistatic media subjected to homogeneous volumetric boundary loading, one proved that the effective behaviour of this media is governing by conventional effective constitutive equation which is intrinsic to the local thermoelasticity theory. It was made by the most exploitation of the popular tools and concepts used in conventional thermoelasticity of CMs and adapted to thermoperistatics. A generalization of the Hills equality to peri-static composites is proved. The classical representations of effective elastic moduli through the mechanical influence functions for elastic CMs are generalized to the case of peristatics, and the energetic definition of effective elastic moduli is proposed. The general results establishing the links between the effective properties (effective elastic moduli, effective thermal expansion) and the corresponding mechanical and transformation influence functions are obtained by the use of the decomposition of local fields into load and residual fields. Effective properties of thermoperistatic CM are expressed through the introduced local stress polarization tensor averaged over the extended inclusion phase. This similarity opens a way for straightforward expansion of analytical micromechanics tools for locally elastic CMs to the new area of random structure peri-dynamic CMs. Detailed numerical examples for 1D case are considered.

Commentary by Dr. Valentin Fuster
2016;():V001T03A045. doi:10.1115/IMECE2016-67317.

One of the most common methods to implement peridynamics numerically is based on the discretization of the whole body by means of a structured and regular grid of nodes and a constant horizon size. That leads to an inefficient use of computational resources as well as to the impossibility to explore the multi-scale capabilities of peridynamics within a unique framework. Adaptive grid refinement and scaling seem to be a promising strategy to reduce those limitations, allowing to increase the resolution of the analysis and to reach the interested length-scale only in the desired regions. The application of such an approach in the peridynamic solutions requires certainly to be investigated, in particular, this is done by the comparison of numerical peridynamic solutions with the analytical solutions of classic linear elasticity theory.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Propulsion

2016;():V001T03A046. doi:10.1115/IMECE2016-65001.

This study presents a numerical simulation of a 3D viscous subsonic flow in the VKI-Genoa turbine cascade taking into account the laminar-turbulent transition. The numerical simulation is performed using the Reynolds-averaged Navier-Stokes (RANS) equations and the low-Reynolds k-ω SST turbulence model. The Langtry’s algebraic Production Term Modification (PTM) model is applied for modeling the laminar-turbulent transition. The governing equations are integrated using the second-order accurate Godunov’s type implicit ENO scheme. Computations of both fully turbulent and transitional flows are carried out. Much attention is given to the comparison between the present numerical results and the existing experimental data. The comparison was based on the surface distributions of the isentropic velocity, the friction velocity, the flow acceleration parameter, the displacement thickness, the shape-factor, and the momentum thickness Reynolds number. Velocity profiles upstream and downstream of the transition onset were compared also. The numerical results obtained show an influence of the transition on the secondary flow pattern. In the case of the transitional flow, when compared with the fully turbulence flow case, the endwall boundary layer cross-flow starts upstream, and it is more intensive, but less massive due to a thinner boundary layer in the laminar flow region.

Commentary by Dr. Valentin Fuster
2016;():V001T03A047. doi:10.1115/IMECE2016-65130.

The design of total temperature probes for accurate measurements in hot, high-speed flows remains a topic of great interest in a number of engineering areas, despite a broad and deep prior literature on the subject. Prediction of error sources from convection, conduction and radiation is still an area of concern. For hot-flow conditions, the probe is normally mounted in a cooled support, leading to substantial axial conduction. Also, radiation plays a very important role in most hot, high-speed conditions. One can apply detailed computational methods for simultaneous convection, conduction and radiation heat transfer, but such approaches are not suitable for rapid, routine design studies. So, there is still a place for approximate analytic methods, and that is the subject of this paper.

Commentary by Dr. Valentin Fuster
2016;():V001T03A048. doi:10.1115/IMECE2016-65373.

This paper investigates by an energetic approach possible new configurations of aircrafts, which can rival in low speed operations against helicopters. It starts from an effective energy balance of helicopters during fundamental operations: takeoff, horizontal flight, hovering, and landing. The energy state of a helicopter can be written as:

E = ½ mV2 + mgh + ½ I ω2 (1)

where m is mass of helicopter, I is total rotor inertia, ω is rotor rotational speed. By taking the partial derivative with respect to time of equation 1, the power is expressed as

dE/dt = ΔP = mV dV/dt + mg dh/dt (2)

By optimizing the energy balance of the helicopter a new aircraft configuration has been obtained that allow a very high lift even at very low speed, but drastically reducing the energy consumption during horizontal flight. The total power required is obtained by rotor power and overall efficiency factor (η) and HPreq total = η HPreq rotor.

By equations (1) and (2) it has been produced a preliminary optimization in different operative conditions considering a speed range from 0.5 (hovering conditions) to 50 m/s. By an accurate balance of the results, it has been identified that the most disadvantageous situation for a helicopter is forward flight. A new powered wing architecture has been specifically studied for replicating the behaviour of helicopters. Preliminary it has been defined by starting from the energy equations the main characteristics of the propelled wing. From those numerical results it has been defined a new configuration of propelled wing and the new aircraft configuration which allow adequate performance against helicopter. Those wings take a large advantage of two not common features: symmetry with respect to a vertical axis and possibility of optimizing the shape for specific missions.

It has been designed and optimized in different configurations by CFD. In particular, an accurate analysis of fluiddynamic of the system allows quantifying the different effects that allows realizing an extraordinary ratio between lift and thrust producing an effective vehicle that can rival against helicopter also at very low speeds with a morphing configuration that will be presented in the final paper because of patenting reasons. Results show that the proposed innovative aircraft configuration allows hovering and very low speed flight. In particular, the conditions and the design for this kind of operation are presented even if still in initial design stage. The presented aircraft architecture can also allow inverting the direction of motion just by inverting the direction of the thrust. In this case, it will allow overcoming completely the performances of helicopters. The energetic balance of flight has been evaluated and the advantages with respect to helicopters have been finally expressed with surprising results.

Topics: Aircraft , Wings
Commentary by Dr. Valentin Fuster
2016;():V001T03A049. doi:10.1115/IMECE2016-66008.

In this paper a design process of a highly loaded profile for a turbine exit case (TEC) application is described. The profile has an increased pitch to chord ratio which is approximately 50% higher compared to conventional airfoils. For the design of the airfoil a two-dimensional (2D) computational fluid dynamics (CFD) prediction method was used in addition to in-house design rules and low Reynolds number experience from previous experiments. Furthermore, common knowledge from turbine and compressor design as well as turbine exit guide vane studies was evaluated and taken as basis for the new design.

To verify the highly loaded design, the profile was tested over a wide Reynolds number range in the high speed cascade wind tunnel of the Institute of Jet Propulsion (ISA) at the University of the German armed forces in Munich.

The experiments showed a very good agreement between the CFD predictions and the measurements for high Reynolds numbers. In the low Reynolds number regime the tendency to massive flow separation was slightly underestimated by the CFD predictions. It is particularly challenging as the CFD predictions still have problems to calculate open separation bubbles. Active flow control (AFC) by fluidic oscillators was also part of the design process and successfully applied on the profile.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Recent Advances in Aerospace Structures and Materials

2016;():V001T03A050. doi:10.1115/IMECE2016-65545.

Design of the new generation of aircraft is driven by the vastly increased cost of fuel and the resultant imperative for greater fuel efficiency. Carbon fiber composites have been used in aircraft structures to lower weight due to their superior stiffness and strength-to-weight properties. However, carbon composite material behavior under dynamic ballistic and blast loading conditions is relatively unknown. For aviation safety consideration, a computational constitutive model has been used to characterize the progressive failure behavior of carbon laminated composite plates subjected to ballistic impact conditions. Using a meso-mechanics approach, a laminated composite is represented by a collection of selected numbers of representative unidirectional layers with proper layup configurations. The damage progression in a unidirectional layer is assumed to be governed by the strain-rate dependent layer progressive failure model using the continuum damage mechanics approach. The composite failure model has been successfully implemented within LS-DYNA as a user-defined material subroutine. In this paper, the ballistic limit velocity (V50) was established for a series of laminates by ballistic impact testing. Correlation of the predicted and measured V50 values has been conducted to validate the accuracy of the ballistic modeling approach for the selected carbon composite material. The availability of this modeling tool will greatly facilitate the development of carbon composite structures with enhanced ballistic and blast survivability.

Commentary by Dr. Valentin Fuster
2016;():V001T03A051. doi:10.1115/IMECE2016-65548.

In this paper, we study fully coupled electromagnetic-elastic behaviors present in the structures of smart beams using variational asymptotic beam sections and geometrically exact fully intrinsic beam equations combined in a consistent theory. We present results for smart beams under various oscillatory loads in both the axial and transverse directions and calculate the corresponding deformations. Recovery equations are employed to construct the full 3D stress and strain components in order to complete a full stress / strain analysis. Smart materials change mechanical energy to electrical energy; therefore, changing the structural dynamic behavior of the structure and its stiffness matrix.

Commentary by Dr. Valentin Fuster
2016;():V001T03A052. doi:10.1115/IMECE2016-66696.

The space structures are realized by combining skin and reinforced components, such as longitudinal reinforcements called stringers and transversal reinforcements called ribs. These reinforced structures allow two main design requirements to be satisfied, the former is the light weight and the latter is a high strength. Solid models (3D) are widely used in the Finite Element Method (FEM) to analyse space structures because they have a high accuracy, in contrast they also have a high number of degrees of freedoms (DOFs) and huge computational costs. For these reasons the one-dimensional models (1D) are gaining success as alternative to 3D models. Classical models, such as Euler-Bernoulli or Timoshenko beam theories, allow the computational cost to be reduced but they are limited by their assumptions. Different refined models have been proposed to overcome these limitations and to extend the use of 1D models to the analysis of complex geometries or advanced materials. In this work very complex space structures are analyzed using 1D model based on the Carrera Unified Formulation (CUF). The free-vibration analysis of isotropic and composite structures are shown. The effects of the loading factor on the natural frequencies of an outline of launcher similar to the Arian V have been investigated. The results highlight the capability of the present refined one-dimensional model to reduce the computational costs without reducing the accuracy of the analysis.

Commentary by Dr. Valentin Fuster
2016;():V001T03A053. doi:10.1115/IMECE2016-67646.

Damage and load sensing is rapidly advancing as driven by vast applications in aerospace and mechanical structures. Recently significant amount of efforts have been reported to develop new piezo-resistive strain sensor made from polymers with carbon nanoparticles, such as carbon nanotubes, carbon nanofibers, and graphene. These nanoparticles with advanced mechanical, electrical, and thermal properties are recognized as potential materials which can enhance mechanical performance and provide beneficial functionalities in polymers and composites. However, most previous research focused on the improvement of material properties for sensing applications. Limited work balanced the sensor design and material innovation for real time strain sensing. In this paper nanocomposite membranes are proposed to accurately measure local strain, especially for the strain sensing and health monitoring in composites. The micro-scale morphology and structures are first experimentally characterized. Both the fabrication process and the nanoparticle concentration are investigated to obtain the optimal sensing capabilities. The sensing function is achieved by correlating the piezoresistance variations to the stress or strain applied on the sensing area. Due to the conductive network formed and the tunneling resistance change in neighboring nanoparticles, the electrical resistance measured will show a clear correlation with the load conditions. The characterized membrane structures have the potential to be further applied to continuously monitor impact loads, especially focusing on low velocity barely visible damage in composites.

Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Recent Advances in Mechanics Composites

2016;():V001T03A054. doi:10.1115/IMECE2016-65821.

The modeling method of fiber-reinforced composites by state-based peridynamics was studied. The one-parameter nonlinear constitutive model was used to get the nonlinear relationship between force vector state and deformation vector state. Then the governing equation for laminate with nonlinear inplane behavior was built. A compensation modification method was also proposed to reduce the surface effects. A scalar function was introduced in the equation of force vector state in order to describe the damage. After the proposed compensation modification method was verified to reduce strain energy error of particles in the boundary region effectively, both unidirectional and orthotropic composite panels under uniaxial tension load were modeled. The resulting stress-strain curves fit well with the test data. Also, progressive damage analysis of composite panels with a center-hole was carried out, and the corresponding damage results agreed well with the experimental and simulating results of a relevant published research.

Topics: Laminates , Modeling , Damage
Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Structural Health Monitoring

2016;():V001T03A055. doi:10.1115/IMECE2016-66167.

This paper presents a generic data-driven failure prognosis method based on adaptive state space models for engineering systems, which integrates adaptive model recognition with a dynamic system model for remaining useful life prediction. The developed approach employs a statistical learning framework for adaptively learning of time-series degradation performance, and then a Bayesian technique for self-updating of data-driven models to adapt the operational or environmental changes. With the developed approach, the prognosis technique can eliminate the dependence to system specific models and be adaptive to system performance changes due to degradation or variation of system operational conditions, thereby yielding accurate remaining useful life predictions. The developed methodology is demonstrated by an engineering case study.

Topics: Failure
Commentary by Dr. Valentin Fuster
2016;():V001T03A056. doi:10.1115/IMECE2016-66505.

In this paper, an effective approach is developed to evaluate fatigue life of smooth specimens of 316 austenitic stainless steel under the fully reversed loading condition based on strain intensity factor and the equivalent initial flaw size (EIFS) concept. The strain intensity factor is indicated to be a better driving parameter to correlate with the fatigue crack growth rate, especially for the fully reversed load condition and the low cycle fatigue region. EIFS is an effective approach to account for complex process of the crack initiation and small crack propagation, which can be calculated by correlating the fatigue limit strain with fatigue threshold strain intensity factor. The fatigue limit strain is obtained from experimental data by analyzing the asymptotic behavior of the fatigue life curve. The driving force of crack growth is expressed in strain intensity factor. Then the fatigue life could be calculated by integrating the crack growth rate from integral lower limit EIFS to integral upper limit critical crack length ac. The experimental data of 316 austenitic stainless steel are employed to validate the proposed model. The good agreements are observed. It has shown that strain-intensity-factor-based approach could be a good method for fatigue life evaluation.

Topics: Fatigue life
Commentary by Dr. Valentin Fuster

Advances in Aerospace Technology: Turbine and Blade Aerodynamics and Performance

2016;():V001T03A057. doi:10.1115/IMECE2016-65260.

Slot-type casing treatment generally has a great potential of enhancing the operating range for tip-critical compressor rotors, however, with remarkable efficiency drop. Part I of this two-part paper was committed to develop a slot configuration with desired stall margin improvement and minimized efficiency loss. Steady simulation was carried out in a 1.5 transonic axial compressor stage at part design rotating speed. At this rotating speed this compressor stage operated at a subsonic condition and showed a rather narrow operating range, which needed to be improved badly. Flow fields analysis at peak efficiency and near stall point showed that the development of tip leakage vortex and resulting blockage near casing resulted in numerical stall. Three kinds of skewed slots with same rotor exposure and casing porosity were designed according to the tip flow field and some empirical strategies. Among three configurations, arc-curved skewed slot showed minimum peak efficiency drop with considerable stall margin improvement. Then rotor exposure and casing porosity were varied based on the original arc-curved skewed slot, with a special interest in detecting their impact on the compressor stability and overall efficiency. Result showed that smaller rotor exposure and casing porosity leaded to less efficiency drop. But meanwhile, effectiveness of improving compressor stability was weakened. The relation between efficiency drop and stall margin improvement fell on a smooth continuous curve throughout all slots configurations, indicating that the detrimental effect of casing treatment on compressor was inevitable. Flow analysis was carried out for cases of smooth casing and three arc-curved configurations at smooth casing near stall condition. The strength of suction/injection, tip leakage flow behavior and removal of blockage near casing were detailed examined. Larger rotor tip exposure and slots number contributed to stronger injection flow. The loss generated within the mixing process of injection flow with main flow and leakage flow is the largest source of entropy increase. Further loss mechanisms were interpreted at eight axial cuts, which were taken through the blade row and slots to show the increase in entropy near tip region. Entropy distributions manifested that loss generations with smooth casing were primarily ascribed to low-momentum tip leakage flow/vortex and suction surface separation at leading edge. CU0 slot, the arc-curved slots with 50% rotor tip exposure, was capable of suppressing the suction surface separation loss. Meanwhile, accelerated tip leakage flow brought about additional loss near casing and pressure surface. Upstream high entropy flow would be absorbed into the rear portion of slots repeatedly, resulting in further loss.

Topics: Compressors , Design
Commentary by Dr. Valentin Fuster
2016;():V001T03A058. doi:10.1115/IMECE2016-65261.

Slot-type casing treatment generally has a great potential of enhancing the operating range for tip-critical compressor rotors, however, with remarkable efficiency drop. In the first part of this two-part words, several configurations of slot casing treatment were tested in a 1.5 transonic compressor stage by steady simulations. One kind of arc-curve skewed slot contributed to considerable stall margin improvement with minimum efficiency loss. However, interaction between main passage and casing treatment was inherently unsteady. Steady simulation was inadequate to provide accurate compressor performance prediction and precise flow field details. Thus, this part was aimed at clarifying the differences between steady and unsteady simulations. The unsteady interaction process between main passage flow and slots were also detailed interpreted. Unsteady simulation was conducted by applying sliding interface between rotor passage and arc-curved skewed slots. Firstly, differences of compressor performance were examined between steady and unsteady methods. Results showed that steady simulation underestimated stall margin improvement and efficiency drop by casing treatment. Then analysis on aerodynamic parameters and specific flow fields were carried out at smooth casing peak efficiency and casing treatment near stall conditions. Unsteady simulation provided more than 50% larger mass flow rate entering or exiting slots opening surfaces at both operating conditions. It revealed that in unsteady simulation, casing treatment contributed to stronger suction/injection process, which promoted tip flow fields more effectively than steady simulation. Axial velocity deficit at rotor outlet was refilled by slots more effectively in unsteady simulation. In steady result, a large low momentum blockage existed inside rotor passage near tip region and prevented flow from entering the passage at near stall condition. While in unsteady simulation at the same condition, incoming flow was still able to travel across rotor passage in a high velocity. Further, instantaneous flow fields near tip region and inside the slots were particularly examined during a rotor blade passing period to elaborate the unsteady flow interaction. The mid-pitch surface of a representative slot was selected to represent the re-circulation procedure inside slots. Unsteady flow fields and spectrum analysis manifested that tip flow field was dominated by slots passing, while re-circulation process inside slots was dominated by blade passing. Low pressure region inside the blade passage facilitated the injection process. Circulation inside slots lagged behind the pressure variations beneath slots. When the slot was striding over the blade tip, intense injection didn’t emerge immediately beneath slots’ front portion. Until the high pressure region moved away from the slot opening surface, fluids inside the slots started to inject into the main flow in high speed.

Commentary by Dr. Valentin Fuster
2016;():V001T03A059. doi:10.1115/IMECE2016-65967.

Performance enhancement in terms of stall margin increment, increased pressure rise coefficient and increased efficiency is of great need for low speed axial fans. Stacking line modifications in terms of sweep, skew, dihedral or combination of these, as well as blade tip geometry modifications are assumed to be one of the ways to achieve finite performance improvement. Non radial stacking of blade profiles modifies secondary flows, tip vortex effects, hub passage vortex and thus affects aerodynamic performance parameters such as stall margin, efficiency, pressure rise, blade loading. In literature many studies have confined to comparison of few cases which led to conflicting results as modification of stacking line may have different effects in different cases. In the present work, comparison of performance of axial fan rotor with three different blade configurations BSL (baseline), SWP (swept blade) and EXTN (swept blade with extended tip) are considered. The BSL configuration is designed on basis of non-free vortex design. The SWP configuration is obtained by shifting radial stacking line of the BSL in axial flow direction by 10° (Forward sweep). The EXTN configuration is obtained by extending tip profile on pressure surface as well as suction surface by 3% locally. Experiments have been conducted on these three configurations to study effects of these modifications on aerodynamic performance. The flow field has been surveyed using Kiel probe, Three hole pressure probe at many flow rates starting from fully open to fully closed. Unsteady flow analysis at exit of rotors of all configurations is carried out using fast response pressure probe. Experimental results show slight performance improvement in terms of increased stall margin, efficiency, as well as total pressure rise for SWP rotor as well as EXTN rotor compared to BSL rotor at low flow coefficients.

Commentary by Dr. Valentin Fuster
2016;():V001T03A060. doi:10.1115/IMECE2016-65978.

Rotor wakes shed from a compressor rotor impinge on downstream blades and is a major source of rotor-stator interaction noise and much research has been dedicated on wake attenuation. Serrated trailing edges is one such wake attenuation technique where the vortices produced at the serrated trailing edges enhance mixing and create a more uniform flow at stator inlet. The present paper investigates the effect of serrations on the trailing edge of a forced vortex axial fan blade. Experimental investigations were carried out at rotor outlet using pneumatic probes and fast response pressure sensors. It is found that total and static pressures reduce in serrated blades due to reduced turning and hence reduced work input. The absolute tangential velocity wake deficit decreases in serration valleys and improvement in axial velocity wake deficit is also found. Improvements as large as 19% and 18% decrease in absolute tangential velocity and axial velocity wake deficit are found at certain radii. The spanwise shape of the wake is altered by the serrations and a wake pattern undulating in the spanwise direction is observed. These are expected to bring down the circumferential variation of the velocity and its phase before entering the next row of blades and bring down the tonal noise.

Topics: Axial flow , Blades
Commentary by Dr. Valentin Fuster
2016;():V001T03A061. doi:10.1115/IMECE2016-66782.

High frequency fluidic oscillators have been of scientific interest for many decades. Especially over the last couple of years fluidic oscillators became more important for active flow control applications. At the Institute of Jet Propulsion of the University of the German Federal Armed Forces Munich studies on different kinds of flow control methods were carried out on aerodynamically highly loaded low pressure turbine blades. On the basis of these studies, the most efficient way to trigger transition at low Reynolds numbers was found to be with fluidic oscillators at frequencies up to 10 kHz.

Still, it is an open issue whether it is most efficient to trigger Tollmien-Schlichting waves, stimulate Kelvin-Helmholtz instabilities or simply induce a frequency independent disturbance in form of a periodic impulse for boundary layer control on aero-dynamically highly loaded low pressure turbine blades. To find an answer to these questions, a high frequency master-slave fluidic oscillator is introduced with an independent frequency and mass flow characteristic. Any frequency from the master oscillator’s characteristic can be chosen and the mass flow rate can be controlled with the slave oscillator. Contrary to concepts with fast switching valves or piezo actuators, this actuator is based on a working principle without the necessity of any moving and life limited parts.

Based on experimental results, the characteristics of the master as well as the coupled oscillator are shown. The predictable operation of the coupled device is demonstrated in detail for a constant overall mass flow rate at discrete frequencies of 5 and 6 kHz. In addition, it is also shown that the mass flow can be varied with one master-slave arrangement by a factor of six while keeping the frequency constant at 5 or 6 kHz, respectively.

Besides proof of concept these investigations focus on relevant parameters for active boundary layer and transition control. The frequency and velocity spectra of the coupled device are presented for constant frequency and constant mass flow operating points. Based on these results the improvement potential of the coupled oscillator for fundamental research on this topic is discussed.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster

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