POD analysis of cavity flow instability

A Mach 1.5 turbulent cavity flow develops large-amplitude oscillations, pressure drag and noise. This type of flow instability affects practical engineering applications, such as aircraft store bays. A simple model of the flow instability is sought towards developing a real-time model-based active control system for simple geometries, representative of open aircraft store bays. An explicit time marching second-order accurate finite-volume scheme has been used to generate time-dependent benchmark cavity flow data. Then, a simpler and leaner numerical predictor for the unsteady cavity pressure was developed, based on a Proper Orthogonal Decomposition of the benchmark data. The low order predictor gives pressure oscillations in good agreement with the benchmark CFD method. This result highlights the importance of large-scale phase-coherent structures in the Mach 1.5 turbulent cavity flow. At the selected test conditions, the significant pressure ‘energy’ content of these structures enabled an effective reduced order model of the cavity dynamic system. Directions and methods to further streamline and simplify the unsteady pressure predictor have been highlighted.