Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R32: Excitation of Turbulent Boundary Layers |
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Chair: Philippe Lavoie, University of Toronto Room: Oregon Ballroom 201 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R32.00001: Measurements of turbulent flow overlying impermeable and permeable walls Taehoon Kim, Gianluca Blois, James Best, Kenneth Christensen There exist an array of natural and industrial flow systems wherein the flow is bounded by a surface that is both permeable and rough (e.g. river beds, bed reactors). In such scenarios, the wall boundary condition is complex as it involves both slip and penetration which together significantly modify the statistical and structural modifications the overlying flow owing to momentum exchange across the wall. The current investigation explores the individual roles of topography and permeability in such flows by systematically decoupling one from the other with a number of wall models having the same porous structure (i.e. cubically arranged spheres; two and five layers, respectively, to highlight the effect of turbulence penetration depth) but with different surface topography (smooth versus cubically arranged hemispheres). High resolution particle-image velocimetry measurements were conducted in the streamwise-wall-normal ($x-y)$ plane and refractive-index matching was employed to optically access the flow within the permeable wall. First- and second-order velocity statistics are used to assess the flow modifications associated with the different wall models and thus ascertain the individual impacts of permeability and topography. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R32.00002: Flows induced by power-law stretching surface motion modulated by arbitrary transverse surface shear Patrick Weidman Boundary-layer solutions for the flow induced by power-law stretching of a plate are obtained for two generalizations that include arbitrary transverse plate shearing. In one extension the power-law motion is a product of the arbitrary transverse shearing motion. In the other extension the streamwise coordinate is added to the transverse shearing motion and together are raised to the power of stretching. In both cases the original boundary-value problem of Banks is obtained, irrespective of the arbitrary transverse shearing motion. [Preview Abstract] |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R32.00003: Experimental investigation of compliant wall surface deformation in a turbulent channel flow. Cao Zhang, Jin Wang, Joseph Katz The dynamic response of a compliant wall under a turbulent channel flow is investigated by simultaneously measuring the time-resolved, 3D flow field (using tomographic PIV) and the 2D surface deformation (using interferometry). The pressure distributions are calculated by spatially integrating the material acceleration field. The Reynolds number is \textit{Re}$_{\tau }=$2300, and the centerline velocity ($U_{\mathrm{0}})$ is 15{\%} of the material shear speed. The wavenumber-frequency spectra of the wall deformation contain a non-advected low-frequency component and advected modes, some traveling downstream at $U_{\mathrm{0\thinspace }}$and others at 0.72$U_{\mathrm{0}}$. Trends in the wall dynamics are elucidated by correlating the deformation with flow variables. The spatial pressure-deformation correlations peak at $y$/$h\approx $0.12 ($h$ is half channel height), the elevation of Reynolds shear stress maximum in the log-layer. Streamwise lagging of the deformation behind the pressure 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) are preferentially associated with ejections, which involve spanwise vortices located downstream and quasi-streamwise vortices with spanwise offset, consistent with hairpin-like structures. The negative deformations (dents) are preferentially associated with pressure maxima at the transition between an upstream sweep to a downstream ejection. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R32.00004: Temporal and Spatial Response of a Turbulent Boundary Layer to Forcing by Synthetic Jets Ronald Hanson, Bharathram Ganapathisubramani, Philippe Lavoie, Tim Berk In this experimental study we examine the spatial and temporal response of a turbulent boundary layer affected by a single, and pair of, synthetic jet actuator(s). The spatial signature of the boundary layer mean-flow has been previously shown to result from large vortical motions caused by the interaction between the synthetic jets and the cross flow. By means of hot-wire measurements, phase-locked to the synthetic jet input, the propagation of the unsteady disturbance can be quantified over the actuation cycle of a synthetic jet. Using long samples both the phase-locked variation of the periodic (actuation cycle) and turbulent fluctuations are examined. It is shown that both the mean flow and turbulence characteristics are markedly different across the span, owing to the three dimensionality of the upstream input. Further, the disturbance shape and phase of the phase-locked disturbance varies significantly with forcing level, in part owing to the disruption of the mean velocity. Particular focus is given to the interaction occurring between the near-wall and outer region scales, which vary across the span, with respect to various forcing conditions. [Preview Abstract] |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R32.00005: Turbulent boundary layer over flexible plates. Parand Rostami, Tindaro Ioppolo This research describes the structure of a turbulent boundary layer flow with a zero pressure gradient over elastic plates. The elastic plates made of a thin aluminum sheets with thickness between 50 and 500 microns were placed on the floor of a subsonic wind tunnel and exposed to a turbulent boundary layer flow with a free stream velocity between 20m/s and 100m/s. The ceiling of the test section of the wind tunnel is adjustable so that a nearly zero pressure gradient is obtained in the test section. Hot-wire anemometry was used to measure the velocity components. Mean, fluctuating velocities and Reynolds stresses will be presented and compared with the values of a rigid plate. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R32.00006: The effect of excitation on the plane wall jet Shibani Bhatt, Sravan Artham, Ebenezer Gnanamanickam The plane wall jet (PWJ) is a unique boundary layer flow in which the highly energetic large-scales of the outer free shear layer transition to turbulence through an inviscid process while, the wall-bounded layer becomes turbulent through a viscous mechanism. These large-scale structures of the PWJ amplitude and frequency modulate the finer scales of the flow much like in canonical boundary layers. However, the unique configuration of the PWJ allows for the independent excitation of the large-scales in the flow to study this interaction with the finer scales. An experimental study is carried out in a PWJ facility operating at friction Reynolds numbers $Re_\tau>$ 1000. The PWJ is excited over three decades of Strouhal number. The changes to the turbulent statistics due to the excitation, across the boundary layer, are presented. It was seen that the excitation alters the energy spectra across the entire boundary layer. Certain scales were excited and others augmented and this modification was a function of the excitation frequency. In general, the energy of the large-scales were more significantly altered when compared to the finer scales. Certain excitation frequencies appear to more dramatically alter the energy of the large-scales with changes also to the wall shear stress. [Preview Abstract] |
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