Abstract

Numerical simulations of particle image velocimetry (PIV) experiments conducted with vortex generating jets (VGJs) on a flat plate, at a Reynolds number based on plate length of 50,000, were performed for three flow conditions using a time-accurate hybrid Navier-Stokes solver. Time-averaged steady blowing of angled jets, subjected to a zero pressure gradient, yielded excellent agreement with the PIV data in terms of vortex formation and strength. Observed flow features include primary and secondary vortices, where the primary vortex eventually dominates the downstream region. A shell wall structure, created by smaller vortical structures surrounding the developing vortices, was also observed. A pulsed jet in a zero pressure gradient was then initialized from a no-control case. A qualitative comparison between averaged experimental and instantaneous numerical results was performed with good agreement in terms of the convected size and distance of the wake. Analysis of the instantaneous numerical flow field agreed well with various flow visualization experiments describing the formation of "kidney" vortices. Various indicators point to the production of a primary vortex by the reduced mass flow of the pulsed jet. Finally, an adverse pressure gradient was applied, inducing a laminar separation zone on the plate. A pulsed angled jet induced strong spanwise vortices in the separated shear layer which appear to weaken the separation zone and allow the bulk jet fluid to flush the remaining low-momentum fluid out of the domain. It is reasonable to assume that reduced blowing ratios and duty cycles would produce similar shear layer vortices and comparable loss reductions. Influences of both turbulent transition and dominant vortical structures were observed, though the spanwise shear layer vortices appear to be critical to the laminar separation reduction scenarios observed in this study.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

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