Jet resonance in truncated ideally contoured nozzle

TL;DR

This study investigates the origin of tonal resonance in overexpanded jets from truncated ideally contoured nozzles, combining experimental and simulation data to understand flow dynamics and pressure fluctuations.

Contribution

It provides a combined experimental and numerical analysis revealing the flow structures and resonance mechanisms responsible for jet tonal behavior in such nozzles.

Findings

Tonal behavior is linked to a specific frequency peak with coherent azimuthal modes.

Upstream and downstream propagating waves coexist within the jet core.

Resonance modulates internal pressure forces and influences shock-wave networks.

Abstract

An overexpanded jet in a truncated ideally contoured nozzle is found to feature a tonal behavior. The flow field is investigated to understand its origin and show how it modifies side-load properties. The temporal and spatial organization of wall pressure and jet velocity field are first experimentally characterized based on synchronized acquisition of both wall-pressure along rings of pressure probes located within the nozzle and high-rate time-resolved PIV velocity fields measured in a plane section crossing the jet downstream of the nozzle exit. The external jet aerodynamics and internal wall pressure field are first shown to be clearly linked, but only at this frequency peak for which a significant coherence emerges between first azimuthal mode of fluctuating wall pressure and first azimuthal mode of fluctuating external velocity field. A Delayed Detached Eddy Simulation is carried out and validated against experimental results in order to reproduce this tonal flow dynamics. The analysis of simulation data shows that the tonal flow behaviour of first azimuthal mode is indeed more largely felt within the whole flow structure where both upstream and downstream propagating waves are shown to co-exist, even far downstream of the nozzle exit. The analysis shows that both waves possess support in the jet core and have a non negligible pressure signature in the separated region. The Spectral Proper Orthogonal Decomposition of fluctuating pressure field at this tonal frequency reveals that the nature and intensity of lateral pressure forces is directed by the resonance related to the upstream- and downstream-propagating coherent structures, which imposes the shock-waves network to respond and modulate the pressure levels on the nozzle internal surface.