Study on post-processing method of supersonic mixing layer simulation results based on streamline tracking

On the time-average, the direction of the mixing layer midline remains essentially the same, with rich conclusions under the Cartesian coordinate system (CCS). However, the static pressure mismatch state of the jet leads to a strong coupling effect of expansion and compression in the mixing process. This causes the midline of the mixing layer to become irregularly curved in shape. It is not convenient to describe with fixed CCS anymore. Therefore, a post-processing method of the flow field is proposed based on streamline tracing using the Lagrangian viewpoint to establish a coordinate system for mixing layer evaluation based on the streamline as the coordinate axis, which is called the Followed Body Coordinate System (FBCS) in this study. The following conclusions are obtained for the velocity thickness, momentum thickness, and Pitot pressure thickness treated by FBCS, and they are in good agreement with each other. In addition, the correction of Pitot pressure thickness after two methods of processing is less than 0.08, and the scalar thickness is insensitive to the choice of coordinate system. The consistency of the corrected velocity thickness and momentum thickness is significantly enhanced. This is due to the fact that the processing in FBCS significantly reduces the effects of airflow velocity and density variations caused by flow expansion and compression. The problem of inaccurate vector thickness evaluation in this state is improved.