Detached eddy simulation of shock unsteadiness in an over-expanded planar nozzle

TL;DR

This study uses Detached Eddy Simulations to analyze shock wave oscillations in an over-expanded planar nozzle, revealing non-stationary pressure fluctuations with amplitude and frequency modulation.

Contribution

It provides detailed spectral analysis of shock unsteadiness using both Fourier and wavelet transforms, highlighting non-resonant low-frequency pressure fluctuations.

Findings

Shock unsteadiness shares features with classical shock wave interactions.

Pressure signals show broad low-frequency content without resonant tones.

Wavelet analysis uncovers amplitude and frequency modulation over time.

Abstract

This work investigates the self-excited shock wave oscillations in a three-dimensional planar over-expanded nozzle turbulent flow by means of Detached Eddy Simulations. Time resolved wall pressure measurements are used as primary diagnostics. The statistical analysis reveals that the shock unsteadiness has common features in terms of the root mean square of the pressure fluctuations with other classical shock wave/boundary layer interactions, like compression ramps and incident shocks on a flat plate. The Fourier transform and the continuous wavelet transform are used to conduct the spectral analysis. The results of the former indicate that the pressure in the shock region is characterized by a broad low-frequency content, without any resonant tone. The wavelet analysis, which is well suited to study non stationary process, reveals that the pressure signal is characterized by an amplitude and a frequency modulation in time.