Reduction of fluctuating pressure loads in shock/boundary-layer interactions using vortex generators

Abstract

Fluctuating wall pressure measurements have been made in a separated shock wave/turbulent boundary-layer interaction produced by an unswept compression corner in a Mach 5 flow. Wheeler doublet vortex generators were placed upstream of the corner to study their effect on the fluctuating pressure loads within the interaction. The vortex generators produce significant three dimensionality in an otherwise two-dimensional interaction. They reduce the upstream influence and the length of the region of separation shock motion by 60 % and 64 %, respectively, and they decrease the maximum wall pressure rms near separation by 23% and shift the fluctuations to higher frequencies. The maximum fraction of energy in the resonant frequency band of typical skin panels (i.e., 100-500 Hz) is decreased by 11%. On the corner face, where the maximum loads occur, the maximum wall pressure rms is reduced by 10%, and the maximum fraction of energy in the 100-500 Hz band is reduced by 35%. These changes are due to a fuller boundary-layer profile, a weaker separation shock, increased boundary-layer turbulence causing increased separation shock jitter, and a shorter region of shock motion. Nomenclature Cf= skin friction coefficient / = frequency f c = separation shock zero crossing frequency G(f) = spectral density function LI = intermittent region length P = pressure Reg = Reynolds number based on momentum thickness T = temperature, separation shock period U = velocity X = stream wise distance normalized by 8, Fig. 1 Y = span wise distance normalized by 8, Fig. 1 Z = vertical distance normalized by 8, Fig. 1 ft = fraction of wall pressure variance in the 100-500 Hz band 8 = undisturbed boundary-layer thickness 8* = undisturbed boundary-layer displacement thickness Y = wall pressure signal intermittency 0 = undisturbed boundary-layer momentum thickness O = undisturbed boundary-layer wake strength parameter a -standard deviation Subscripts max = maximum value pw = wall pressure rms = root mean square value t = pitot pressure vg = vortex generator w = wall oo, inf = freestream condition 0 = stagnation quantity

Effects of Micro-Ramps on a Shock Wave/Turbulent Boundary Layer Interaction

“…A velocity deficit is present downstream of the vertices of each ramp, consistent with results found at free-stream Mach numbers ranging from 1.5 to 5 by Barter and Dolling [12] and Holden and Babinsky [16]. Conversely, Pitt Ford and Babinsky [13] reported that close to the wall at y/δ = 0.1, the mean velocity is highest downstream of a vertex; a discrepancy that is tentatively linked to differences in vortex migration due to different characteristics of the boundary layer (see [9]).…”

“…The micro-ramp is one particular type of SBVGs, which has been shown to reduce the length of the separated region, causing a more abrupt pressure rise (see, e.g., [11][12][13]), as well as a stabilization of the interaction region [14]. Although experimental studies (see [15,16]) suggest that vane-type SBVGs may be more effective in suppressing separation, micro-ramps offer the advantage of being more rugged, therefore less subject to mechanical failure, which is essential for engine intake applications.…”

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

“…Their typical height is about 50% of the boundary layer thickness and their effectiveness comes from the two counter-rotating vortices it introduces in the flow [4]. These vortices transport high-momentum fluid towards the wall, thus creating a fuller boundary layer profile, allowing the flow to pass through the shock system with less separation [5][6][7][8]. Anderson et al [9] used Reynolds Averaged Navier Stokes (RANS) simulations to show that micro-ramps can reduce the incompressible shape factor of the incoming boundary layer to the same level as obtainable with boundary layer bleed.…”

Effect of a Stick on the Flow Field in a Cyclone and the Pressure Drop Reduction Mechanism

“…Therefore the Repds decreases the drag (pressure drop) for the entire ow. Considering this analysis and some methods used to reduce drag on airfoils (Barter and Dolling 1995), the authors propose that the drag in turbulent ows can be reduced by adding vortexes. …”