Incipient Separation in Shock Wave Boundary Layer Interactions as Induced by Sharp Fin

TL;DR

This study investigates the incipient separation caused by shock wave interactions with turbulent boundary layers at sharp fins, comparing theoretical predictions with experimental data and explaining the physical mechanisms involved.

Contribution

It refines understanding of incipient separation mechanisms and improves prediction accuracy by analyzing flow patterns and discrepancies in existing theories.

Findings

Predicted incipient separation aligns with experimental data when considering flow pattern analysis.

Discrepancies in predictions are due to assumptions about streamline behavior behind shock waves.

A correction correlation for incipient separation angle is proposed.

Abstract

The incipient separation induced by the shock wave turbulent boundary layer interaction at the sharp fin is the subject of present study. Existing theories for the prediction of incipient separation, such as those put forward by McCabe (1966) and Dou and Deng (1992), can have thus far only predicting the direction of surface streamline and tend to over-predict the incipient separation condition based on the Stanbrook's criterion. In this paper, the incipient separation is firstly 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 the 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\ aligning with one ray from the virtual origin as the strength of 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 the 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.