Influence of Three-Dimensional Self-Rotation to Top-Large-Separation-to-Bottom-Large-Separation Transition of Oblique Shock Train

Oblique shock train is a common phenomenon in supersonic internal flow, where the mechanism of the asymmetric pattern is still unknown. This paper examines the asymmetric oblique shock train in a Mach number 2.5 flow, and the transition process between top large separation (TLS) and bottom large separation (BLS) has become a key focus of research. The three-dimensional structure of the shock train is investigated from both [Formula: see text] and [Formula: see text] plane perspectives based on schlieren images, which, respectively, exhibit the separation pattern of the shock train on the top/bottom and side walls. Accordingly, the “self-rotation” of the shock train is proposed to explain the TLS-to-BLS transition phenomenon. Experimental results demonstrate that TLS-to-BLS transition is not a two-dimensional process. The TLS-to-BLS transition experiences an intermediate mode, named side large separation (SLS) in this paper, which is similar to a symmetric pattern, while in fact, it is an asymmetric pattern from another plane’s perspective. SLS mode indicates that the three-dimensional shock train holds an asymmetric pattern and rotates 90° around the flow direction; then SLS switches to BLS by rotating another 90°. Consequently, the TLS-to-BLS transition of oblique shock train can be attributed to 180° self-rotation around the flow direction.