Incipient separation in shock wave/boundary layer interactions as induced by sharp fin
The incipient separation induced by the shock wave/turbulent boundary layer interaction at the sharp fin is the subject of the present study. Existing theories for the prediction of incipient separation, such as those put forward by McCabe (1966) and Dou and Deng (1992), can thus far only predic the direction of surface streamline and tend to overpredict the incipient separation condition based on the Stanbrook’s criterion. In this paper, the incipient separation is first predicted with Dou and Deng (1992)’s theory and then compared with Lu and Settles’ (1990) experimental data. The physical mechanism of the incipient separation as induced by the shock wave/turbulent boundary layer interactions at sharp fin is explained via surface flow pattern analysis. Furthermore, the reason for the observed discrepancy between the predicted and experimental incipient separation conditions is clarified. It is found that when the wall-limiting streamlines behind the shock wave becomes aligned with one ray from the virtual origin as the strength of the shock wave increases, the incipient separation line is formed at which the wall-limiting streamline becomes perpendicular to the local pressure gradient. The formation of this incipient separation line is the beginning of the separation process. The effects of Reynolds number and Mach number on incipient separation are also discussed. Finally, a correlation for the correction of the incipient separation angle as predicted by the theory is also given.
Quasiconical free interaction between a swept shock and a turbulent boundary layer
Previous observations that fin-generated interactions are quasiconical in nature were further confirmed by surface pressure measurements spanning Mach 2.5-3.5, which encompassed unseparated through strongly separated interactions. For strongly separated interactions in which the shock wave is bifurcated into a X.-foot structure, the conical free interaction hypothesis was validated through an appropriate scaling of the far-field surface pressure distribution. The behavior of the \-foot structure, such as the decrease of the slope of the separation shock with interaction strength, was explained by invoking the conical free interaction hypothesis. Through the conical free interaction hypothesis, it was further shown that the triple-shock intersection behaves in a complicated manner with changes in interaction strength.
Upstream influence and separation scales in fin-induced shock turbulent boundary-layer interaction
An experimental study has been made of the effects of leading-edge geometry on the upstream influence and separated flow length scales in fin-induced shock wave turbulent boundary-layer interaction. The fins used had wedge-shaped, hemicylindrical and elliptic leading edges and were tested under adiabatic conditions at Mach 4.9. The primary objective was to determine if the length scales generated by different leading edges could be understood within a common framework. To a first approximation the normalized centerline length scales correlate with fin leading-edge drag coefficient. Attempts to correlate additional data at Mach 1.98 and 2.48 from other studies resulted in a reasonable correlation for upstream influence, but that for the separation length showed a clear influence of Mach number. The fact that the upstream influence can be reasonably well correlated in this form lends further support to the view that large-scale three-dimensional vortical separated flows of this type may be largely inviscid dominated.