Characterization of turbulent supersonic flow over a backward facing step through POD

TL;DR

This study investigates turbulent supersonic flow over a backward facing step at Mach 2 using LES and POD, revealing complex flow structures, vortex dynamics, and instabilities with good agreement to experimental data.

Contribution

It combines LES and POD techniques to analyze flow physics and coherent structures in supersonic flow over a backward facing step, providing detailed flow feature insights.

Findings

Identification of vortex structures near the step and along the shear layer.

Revealed Kelvin-Helmholtz instabilities in the shear layer.

Flow features consistent with experimental measurements.

Abstract

The present work reports on the flow physics of turbulent supersonic flow over backward facing step (BFS) at Mach 2 using LES methodology where the dynamic Smagorinsky model is used for SGS modeling, while POD is invoked to identify the coherent structures present in the flow. The mean data obtained through the computations is in good agreement with the experimental measurements, while the iso-surfaces of Q-criterion at different time instants show the complex flow structures. The presence of counter rotating vortex pair in the shear layer along with the complex shock wave/boundary layer interaction leading to the separation of boundary layer is also evident from the contours of both Q and the modulus of vorticity. Further, the POD analysis reveals the presence of coherent structures, where the first and second modes confirm the vortical structures near the step as well as along the shear layer in the downstream region; while the second, third and fourth modes confirm the presence of vortices along the shear layer due to Kelvin-Helmholtz (K-H) instability. Moreover, POD as well as frequency analysis is extended at different planes to extract the detailed flow features.