Stabilizing effects of a perforated splitter plate on a backwards-facing step

Abstract

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We study a modified backwards-facing step flow, with the addition of two different splitter plates; one is a baseline, impermeable plate and the second a perforated one. An experimental investigation is carried out for a turbulent reattaching shear layer downstream of the two plates. The proposed setup is a model configuration to study how the plate characteristics affect the separated shear layer, and also how turbulent kinetic energies and large-scale coherent structures are modified. Hot-wire measurements show that the perforated plate changes the mean profile, mostly by reducing the intensity of backflow close to the bottom wall. Disturbance amplitudes are significantly reduced up to 5 step-heights downstream the trailing edge of the plate, more specifically in the recirculation region. A loudspeaker is then used to introduce phase-locked, low-amplitude perturbations up- stream of the splitter plates, and phase averaged measurements allow a quantitative study of large-scale structures in the reattaching shear-layer. The evolution of such coherent structures are evaluated in light of linear stability theory, comparing the eigenfunction of the Kelvin-Helmholtz mode to the experimental results. We observe a close match of linear- stability eigenfunctions with phase-averaged amplitudes for all tested Strouhal numbers. The perforated plate is found to reduce the amplitude of the Kelvin-Helmholtz coherent structures in comparison to the baseline, impermeable plate, a behavior consistent with the predicted amplification trends from linear stability.