Measurements of a forced, turbulent boundary layer over an elastic surface*

Since the seminal work of Kramer (1957), there has been scientific interest in surfaces that deform under fluid motion. Such compliant surfaces have potential in passive flow control, e.g. vibration damping or skin-friction drag reduction, through careful design of the surface properties. This requires an understanding of the fluid-structural interaction. However, for a turbulent boundary layer (TBL), the inherently broadband spectrum makes it difficult to isolate critical relationships between surface and flow.

Here, an elastic, gelatin surface is embedded in a submerged flat plate, over which a TBL is developed. Addressing the aforementioned broadband complexity, a 2D, traveling-wave-like disturbance is forced into the flow just upstream of the compliant surface through a dynamic roughness element (Jacobi & McKeon, 2011). This wave isolates a spatio-temporal scale and dominates the responses of both the fluid and surface, supporting a reduced input-output analysis. Flow and surface measurements are made by 2D PIV and 3D DIC, phase-locked to the roughness motion. We describe the experiment and the interaction of the forced TBL and compliant surface, with an ultimate view to extend to a broadband spectrum.