Experiments and Modeling of a Compliant Wall Response to a Turbulent Boundary Layer with Dynamic Roughness Forcing

David P Huynh,Yuting Huang,Beverley J Mckeon

doi:10.3390/fluids6050173

David P Huynh, Yuting Huang + Show 1 more

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https://doi.org/10.3390/fluids6050173

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Abstract

The response of a compliant surface in a turbulent boundary layer forced by a dynamic roughness is studied using experiments and resolvent analysis. Water tunnel experiments are carried out at a friction Reynolds number of Reτ≈410, with flow and surface measurements taken with 2D particle image velocimetry (PIV) and stereo digital image correlation (DIC). The narrow band dynamic roughness forcing enables analysis of the flow and surface responses coherent with the forcing frequency, and the corresponding Fourier modes are extracted and compared with resolvent modes. The resolvent modes capture the structures of the experimental Fourier modes and the resolvent with eddy viscosity improves the matching. The comparison of smooth and compliant wall resolvent modes predicts a virtual wall feature in the wall normal velocity of the compliant wall case. The virtual wall is revealed in experimental data using a conditional average informed by the resolvent prediction. Finally, the change to the resolvent modes due to the influence of wall compliance is studied by modeling the compliant wall boundary condition as a deterministic forcing to the smooth wall resolvent framework.

Highlights

One of the long-standing engineering goals for research in wall-bounded turbulent flows is to develop design capabilities for flow control mechanisms
This work utilized experiments and resolvent analysis to study the response of a compliant surface to the dynamic roughness forced synthetic mode in a turbulent boundary layer
The resolvent modes highlighted the ‘virtual wall’ feature as a result of the compliant surface, identifying the change in near-wall structure of the resolvent modes arising from the change in boundary condition, and provided a method to model the effect of the boundary condition as an additional forcing

Summary

Introduction

One of the long-standing engineering goals for research in wall-bounded turbulent flows is to develop design capabilities for flow control mechanisms Designing such control schemes within the broad field of possible applications and strategies [1] is difficult due to the essential complexity of actuator–flow interaction, and the often vast operational parameter space associated with actuation design. Compliant surfaces embody both of these challenges, presenting a coupled fluid-structural problem and nearly limitless regime of surface material properties. Tempering some of the optimistic experimental findings are more recent Direct Numerical Simulation (DNS) studies

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