Evolution and Control of Streamwise Vortices formed by Flow Circulations in a Rectangular Bend

Counter-rotating Dean circulations that form by flow turning within bends lead to the rollup and advection of induced streamwise vorticity concentrations of opposite sense that persist downstream of the bend and intensify inherent flow non-uniformities and losses. A joint experimental-numerical investigation of the flow within a rectangular bend shows that the circulations transport streamwise vorticity of opposite sense along each of the bend’s side walls that accumulate antisymmetrically about the center of the inner bend surface and roll up to form a pair of counter-rotating vortices along its center plane. This formation mechanism spurred an approach for mitigating the adverse effects of the vortex pair by throttling the vorticity transport of the Dean circulations to diminish the strength of each vortex using an array of opposing sense, small scale co-rotating streamwise vortices along each half of the bend’s inner surface. Each vortex in the control array is formed by a fluidically oscillating wall jet embedded just upstream of the bend. Successful suppression of the base flow vortices coupled with significant reduction in flow distortions were demonstrated over a range of Mach numbers (0.3 < M < 0.5), bend angles, and inner radii .