Effect of Shock/Boundary-Layer Interaction

Shock/boundary-layer interaction, Section 9.2, happens where the bow shock of the flight vehicle, or embedded shocks interfere with the boundary layer on the vehicle surface. This may happen in the external flow path of an airframe including the outer part of inlets, see, e. g., Figs. 6.4 to 6.6, at control surfaces, or in the internal flow path of propulsion systems, see, e. g., Figs. 6.5 and 6.7.

If a shock wave impinges on a (laminar) boundary layer, the flow proper­ties of the latter change, even if the flow does not become separated locally or globally. We have also seen in Sub-Section 6.6 that the unit Reynolds number across a ramp shock changes, which, of course, changes the flow properties of the boundary layer across the shock, too. Depending on Reynolds num­ber, shock strength etc. the stability properties of the boundary layer will be affected.

Although this phenomenon is potentially of importance for hypersonic flight vehicles, it has found only limited attention so far. For ramp flow, for instance,—with trim and control surface heating in the background (includ­ing the presence of Gortler instability, see below)—experimental data and data from dedicated numerical studies, e. g., [58], have been assembled and summarized in [59].

We note further a stability investigation of shock/boundary-layer inter­action in a Me = 4.8 flow with linear stability theory and direct numerical simulation (DNS) [60]. It was shown that and how second-mode instability is promoted by the interaction. Linear stability theory yielded results in good agreement with DNS for wall-distant disturbance-amplitude maxima with small obliqueness angles. For large obliqueness angles and wall-near ampli­tude maxima accuracy of linear stability theory deteriorated considerably in comparison to DNS. The results show that both the effect and the related simulation problems warrant further investigations.

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