Microramps Upstream of an Oblique-Shock/Boundary-Layer Interaction

Abstract

To examine the potential of micro vortex generators for shock/boundary-layer interaction control, a detailed experimental and computational study in a supersonic boundary layer at M 3:0 was undertaken. The experiments employed a flat-plate boundary layer with an impinging oblique shock with downstream total-pressure measurements. The moderate Reynolds number of 3800 allowed the computations to use monotone-integrated large eddy simulations. The monotone-integrated large eddy simulations predictions indicated that the shock changes the structure of the turbulent eddies and the primary vortices generated from the microramp. Furthermore, they generally reproduced the experimentally obtained mean velocity profiles, unlike similarly resolved Reynoldsaveraged Navier-Stokes computations. The experiments and monotone-integrated large eddy simulations results indicate that the microramps, for which the height is h 0:5, can significantly reduce boundary-layer thickness and improve downstream boundary-layer health as measured by the incompressible shape function H. Regions directly behind the ramp centerline tended to have increased boundary-layer thickness, indicating the significant threedimensionality of the flowfield. Compared with baseline sizes, smaller microramps yielded improved total-pressure recovery. Moving the smaller ramps closer to the shock interaction also reduced the displacement thickness and the separated area. This effect is attributed to decreased wave drag and the closer proximity of the vortex pairs to the wall. Nomenclature A sep = separation area a = speed of sound c = cord length of the microramp D = width of the computational domain d = width of the microramp dt = differential time dx = differential length in the streamwise direction dy = differential length in the normal direction dz = differential length in the spanwise direction E = height of the computational domain H = incompressible shape factor h = microramp height L = length of the computational domain M = Mach number P = pressure P o = total pressure Re ref = Reynolds number based on ref s = spacing between adjacent microramps at the centerline T = temperature t = fluid convection time scale U = average streamwise velocity U = frictional velocity u = instantaneous streamwise velocity u 0 = streamwise fluctuation the velocity v = normal velocity w = spanwise velocity W = weighting function x = streamwise distance y = normal distance relative to solid wall z = spanwise distance relative to center of domain = total-pressure recovery factor = frictional velocity ratio = specific heat ratio t = time step x = streamwise length of the computational cell = boundary-layer thickness ref = displacement thickness at x 0 but with no shock effects = k direction in the computational domain = wall normal coordinate normalized by boundarylayer thickness = von Kármán constant = i direction in the computational domain = integration time = integration time normalized by the freestream flow convection time ! = kinematic viscosity at wall = j direction in the ...

Flow control of an oblique shock wave reflection with micro-ramp vortex generators: Effects of location and size

“…In set E, three 4 mm micro-ramps were mounted next to each other in the tunnel (see Fig.1(b)). The spacing s between the centre lines of the micro-ramps equals 7.5h = 30 mm, which is the value recommended by Anderson [9] and the one commonly used by other researchers in this field [8,10,11]. Finally, in set F the undisturbed shock wave boundary layer interaction is investigated, which will serve as a reference for all other cases.…”

“…The work of Lee [11] showed that RANS computations are not very well suited for these kind of problems and deliver results that deviate significantly from experimental data. Large Eddy Simulations (LES) simulations on the other hand produce results that are much closer to the experimental evidence.…”

Decay of the supersonic turbulent wakes from micro-ramps

“…Numerical simulations by Lee et al [11] using implicit large eddy simulation (ILES) described the decay of streamwise velocity component through the cross-sectional contours. A Reynolds-averaged Navier-Stokes (RANS) simulation with immersed-boundary treatment was performed by Ghosh et al [12] (Ma=2.5, h/δ=0.46, 0.92) and the velocity profiles were compared with experiment data [8].…”

LES investigation into the generation of momentum deficits in the supersonic wake of a micro-ramp

“…The positive effects of the micro-ramp have been reported in the preceding researches. A typical application is intended for separation reduction produced in a shock wave/boundary layer interaction (SWBLI) [2][3][4][5][6][7][8] . Although the effects have been demonstrated through the foregoing studies, the flow physics of the microramp has not been fully understood due to the complex geometry of current device.…”