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Effects of Fluctuating Pressure Gradients on Boundary Layer Turbulence

[+] Author Affiliations
Pranav Joshi, Xiaofeng Liu, Joseph Katz

Johns Hopkins University, Baltimore, MD

Paper No. FEDSM2013-16249, pp. V01CT29A003; 14 pages
doi:10.1115/FEDSM2013-16249
From:
  • ASME 2013 Fluids Engineering Division Summer Meeting
  • Volume 1C, Symposia: Gas-Liquid Two-Phase Flows; Industrial and Environmental Applications of Fluid Mechanics; Issues and Perspectives in Automotive Flows; Liquid-Solids Flows; Multiscale Methods for Multiphase Flow; Noninvasive Measurements in Single and Multiphase Flows; Numerical Methods for Multiphase Flow; Transport Phenomena in Energy Conversion From Clean and Sustainable Resources; Transport Phenomena in Materials Processing and Manufacturing Processes; Transport Phenomena in Mixing; Turbulent Flows: Issues and Perspectives
  • Incline Village, Nevada, USA, July 7–11, 2013
  • Conference Sponsors: Fluids Engineering Division
  • ISBN: 978-0-7918-5556-0
  • Copyright © 2013 by ASME

abstract

This study investigates the effects of fluctuating pressure gradients on boundary layer turbulence. Two-dimensional (2D) time resolved particle image velocimetry (PIV) measurements have been performed in a zero pressure gradient (ZPG) boundary layer. The streamwise and wall-normal (x, y) components of the fluid material acceleration (Du/Dt and Dv/Dt, respectively) are integrated spatially to obtain the pressure distributions. Large scale pressure fluctuation gradients are found to involve three dimensional flow structures. Ejections, high wall-normal enstrophy flux, and viscous vorticity production occur mostly during periods of ∂p′/∂x < 0 as the fluid accelerates by moving away from the wall. Conversely, fluctuating adverse pressure gradients (∂p′/∂x > 0) are preferentially associated with sweeps, as fluid approaching the wall is decelerating. Consequently, the outward transport of small-scale turbulence is suppressed, and the near-wall enstrophy increases. The instability of the flow associated with the adverse pressure gradients might also contribute to the increased production of near-wall turbulence. Results also indicate that the regions of fluctuating adverse and favorable pressure gradients are likely to be associated with the downwash and upwash sides, respectively, of very large scale roller structures, several boundary layer thicknesses in length.

Copyright © 2013 by ASME

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