Surface-Pressure Measurements of Bi-stability on BeVERLI Hill

Over the past two decades, several experimental campaigns have been conducted with hill geometries in an effort to improve our knowledge on the behaviour of turbulent boundary layer flows subject to pressure gradients and surface curvature effects. The Benchmark Validation Experiments for RANS and LES Investigations (BeVERLI) project is being conducted to collect detailed experimental datasets of the flow over a three-dimensional hill geometry. Mean and unsteady surface-pressure measurements were collected at the Virginia Tech Stability Wind Tunnel and the recirculating wind tunnel at the University of Toronto Institute for Aerospace Studies. Results obtained at the two facilities are compared to evaluate their sensitivity to extrinsic experimental conditions. The results for the 0^? model orientation and model height based Reynolds numbers from 165,000 to 325,000 are presented. For this orientation, the wake is bi-stable in nature. The behaviour of this phenomena is explored by tracking the time elapsed between switching events, conditional averaging of the two modes, and proper orthogonal decomposition of the surface-pressure field. It is shown that the mean surface-pressure distributions of the two modes are symmetrical about the hill centerline. Furthermore, a favouring toward one mode is observed from the measurements collected at Virginia Tech. This is associated with an asymmetry in wall conditions at the test facility indicating the sensitivity of the bi-stable flow to extrinsic conditions.