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CEAFM Presentation: Experimental Characterization of Compliant Wall Deformation in a Turbulent Channel Flow

  • March 12, 2018
  • 4:00 p.m.
  • 260 New Classroom Building
  • Dr. Joseph Katz, Johns Hopkins University
  • Faculty Host: Dr. Devenport

Abstract: Interaction of a compliant wall with a turbulent channel flow is investigated by simultaneously measuring the time-resolved, three-dimensional flow field and the two-dimensional surface deformation. The optical setup integrates time-resolved tomographic particle image velocimetry to measure the flow with Mach-Zehnder interferometry to map the deformation. For the initial series of tests, the Reynolds number is Reτ=2300, and the Young’s Modulus of the wall is 0.93 MPa, resulting in a ratio of shear speed to mean flow velocity of 6.8. The wavenumber-frequency spectra of deformation contain a non-advected low-frequency component and advected modes, some traveling at the centerline velocity (U0) and others at 0.72U0. The amplitudes of advected modes are much smaller than the wall-unit, hence they are not expected to affect the flow. Trends in the wall dynamics are elucidated by correlating the deformation with flow variables, including the 3D pressure distribution, and by comparison to predictions of the Chase (1991) linear model. The spatial pressure-deformation correlations peak in the log-layer, but the deformation lags behind the pressure in the streamwise direction. The latter is caused in part by phase-lag of the pressure with decreasing distance from the wall, and in part by material damping. Positive deformations (bumps) associated with negative pressure fluctuations are preferentially located between legs of hairpin vortices. The negative deformations (dents) associated with positive pressure fluctuation peaks are located at the transition between an upstream sweep to a downstream ejection. Using the Chase model for guidance, recent measurements where the shear speed is matched with the liquid velocity show orders of magnitude increase in deformation amplitude to several wall units, which are expected to modulate the flow structure.

Bio: Joseph Katz received his B.S. degree from Tel Aviv University, and his M.S. and Ph.D. from California Institute of Technology, all in mechanical engineering. He is the William F. Ward Sr. Distinguished Professor of Engineering, and the director and co-founder of the Center for Environmental and Applied Fluid Mechanics at Johns Hopkins University. He is Fellow of the American Society of Mechanical Engineers (ASME) and the American Physical Society. He has served as the Editor of the Journal of Fluids Engineering, and as the Chair of the board of journal Editors of ASME. He has co-authored more than 350 journal and conference papers. Dr. Katz research extends over a wide range of fields, with a common theme involving experimental fluid mechanics, and development of advanced optical diagnostics techniques for laboratory and field applications.