Experimental Investigation of interaction between the flow field and wall deformation in turbulent boundary layers over compliant surfaces

Recent investigations of turbulent boundary layers over compliant surfaces have revealed the dominant effect of flow features in the logarithmic layer on the wall deformation. Two-way coupled interactions occur when the deformation magnitude becomes comparable to the viscous wall unit. The present simultaneous measurements of time-resolved volumetric flow field and spatial distribution of wall deformation are performed using an integrated system involving tomographic PTV for measuring the flow, and Mach Zehnder interferometry for mapping the wall deformation. The measurements are performed in a refractive index matched water tunnel at Re_τ ranging from 3,000 to 9,000, and E/ρU² (E- Young’s modulus) from 1.8 to 22. The unstructured velocity and material acceleration are interpolated onto a structured grid using a physics-based constrained cost minimization method. The pressure field is computed by spatial integration of the material acceleration using a GPU-based omni-directional code. Spectral analysis and conditional statistics are used for characterizing the coupling between flow variables (velocity, vorticity, and pressure) and deformation features, highlighting mechanisms that increase the turbulence level and modify the mean velocity profile near the wall.