Resolvent Analysis of an Under-expanded Planar Supersonic Impinging Jet

TL;DR

This paper uses resolvent analysis and LES data to study the instability mechanisms and actuator effects on a Mach 1.27 under-expanded impinging jet, providing insights for active flow control strategies.

Contribution

It applies resolvent analysis to an under-expanded jet and compares the modes with LES data, exploring actuator effects for noise control and flow stabilization.

Findings

Kelvin-Helmholtz instability dominates energy amplification.

Resolvent modes agree with SPOD modes from LES.

Actuator forcing location and type significantly affect energy amplification.

Abstract

This investigation aims to assess the effect of different types of actuator forcing on the feedback loop of an under-expanded Mach 1.27 planar impinging jet using a resolvent framework. To this end, we employ a Large Eddy Simulation database as a truth model. The time and spanwise-averaged mean flow is taken as an input to global stability and resolvent analyses with the purpose of examining both the intrinsic instability and input-output characteristics. The results show that the inherent instability and primary energy amplification are attributed to the Kelvin-Helmholtz (K-H) instability. Moreover, the K-H response modes obtained from the resolvent analysis are in reasonable agreement with Spectral Proper Orthogonal Decomposition (SPOD) modes from the unsteady LES data. Insights into noise control are obtained by localizing the actuator forcing to the nozzle lip and the ground plate by imposing component-wise forcing to mimic different notional actuators. It is observed that energy amplification obtained for the localized component-wise forcing is different from the global resolvent analysis and dependent on the type of actuator. This provides insights into the type, wavenumber, and frequency of actuators for active flow control.