Large-Eddy Simulation of an over-expanded planar nozzle

TL;DR

This study uses Large-Eddy Simulation to visualize and analyze the unstable shock behavior in an over-expanded planar nozzle, revealing detailed flow physics and mechanisms behind shock instability.

Contribution

First LES-based visualization of shock instability in an over-expanded planar nozzle, confirming experimental findings and providing detailed flow physics insights.

Findings

Confirmed shock instability and asymmetry in the flow

Visualized shock-boundary layer interactions and flow separation

Suggested mechanisms for shock instability through low-frequency shock motion

Abstract

This fluid dynamics video shows visualizations of a Large-Eddy Simulation (LES) of an over-expanded planar nozzle. This configuration represents the experimental setup of Papamoschou et. al. which found the position of the internal shock to be unstable. Our LES calculations confirm this instability and offer a vibrant and dynamic view of the underlying flow physics. The interaction between shock and turbulent boundary layer is shown as is the subsequent separation region downstream. Numerical Schlieren provide a glimpse of the low frequency shock motion and suggest potential mechanisms for the instability. Key features include the asymmetry of the shock structure (with large and small lambda shocks), compression and expansion waves downstream of the shock and large scale flow reversal. Full details of the experiment and the calculation can be found in the references.