Shock wave–boundary layer interactions in rectangular inlets: three-dimensional separation topology and critical points

Abstract

The interaction between two separated flow regions was studied for the fundamental problem of a shock wave-boundary layer interaction (SBLI) within a rectangular inlet. One motivation is that the inlet of an engine on a supersonic aircraft may contain separation zones on the sidewalls and the bottom wall; if one region separates first it can alter the flow on the other wall and lead to engine unstart. In our work an oblique shock wave was generated by a wedge suspended from the upper wall of a Mach 2.75 wind tunnel. Stereo particle image velocimetry (PIV) measurements were recorded in 25 planes that include all three possible orthogonal orientations. The lateral velocity and vorticity measurements help to explain the underlying flow structure and these quantities were not measured previously for this problem. It is concluded that the sidewall and bottom wall separation zones interact due to an underlying flow structure that is similar to the two types of 3-D separation patterns previously described by Tobak & Peake (Annu. Rev. Fluid Mech., vol. 14, 1982, pp. 61-85). Separation first occurs at an upstream location where the shock interacts with the sidewall. Lateral velocities direct flow toward the centreline to cause separation on the bottom wall. This causes significant curvature of the shock wave, so that even the region near the tunnel centreline cannot be explained by conventional 2-D concepts. A number of critical points (saddle points, nodes, focus points) were identified. Results are consistent with the general ideas of Burton & Babinsky (J. Fluid Mech., vol. 707, 2012, pp. 287-306) and help to provide details of how the sidewalls redistribute the adverse pressure gradient in space.

Effects of Compressibility and Shock-Wave Interactions on Turbulent Shear Flows

“…The problem also includes the possible interaction between the two regions in the corner area which may have its own vortex and separation structure. Eagle & Driscoll (2014) used stereo PIV to measure all three velocity components, showing details of the corner vortices and showing the need to consider the full 3D problem for shock interactions in low To illustrate the flow phenomena, we consider the configuration from Wang et al (2015), which included both sidewalls in an M ∞ = 2.7 interaction of an oblique shock with a flat plate boundary layer and was simulated using wall-resolved LES. The M ∞ = 2.7 upstream boundary layer is not expected to experience strong compressibility effects until it enters the region of interaction with an oblique shock that is strong enough to separate the flow.…”

Turbulence characteristics of supersonic corner flows in a low aspect ratio rectangular channel

“…This design was selected to produce an equilibrium flat plate boundary layer [19] in an attempt to minimize pressure gradients history effects and Görtler vortices on the boundary layer developing on the bottom-wall (floor) of the wind tunnel. Since our previous work has focused on a 3D SBLI configuration and this work is an effort to better understand it, we use the same coordinate system of our previous SBLI work [3,20,21,22]. In particular, the origin of the coordinate system is centered at the location of the leading edge of the full-span 6 o shock generator wedge (which is about 481.5mm downstream of the nozzle throat) used in our previous work on 3D SBLI.…”

Sidewall Gap Effects on Oblique Shock-Wave/Boundary-Layer Interactions

“…However, little research has been conducted on the extent to which a two dimensional experimental arrangement can be expected to generate two dimensional flow. Underscoring this are recent studies which suggest that nominally two dimensional experimental arrangements can result in flows featuring significant three-dimensional properties [3][4][5].…”

“…However, variations in the extent of sidewall interaction exist. For practical reasons of test article movement, some SWBLI studies have employed a small gap between the test article and sidewall [4,[6][7][8], while others (including most numerical investigations due to meshing constraints) perform experiments with full span test articles [5,[9][10][11][12]].…”