Space-time proper orthogonal decomposition of actuation transients: plasma-controlled jet flow

TL;DR

This study uses space-time POD to analyze the transient dynamics of a plasma-actuated turbulent jet flow transitioning from stationary to cyclostationary states, revealing low-rank structures and flow deformation mechanisms.

Contribution

It introduces a novel application of space-time POD to characterize actuation-induced transients in turbulent jet flows under plasma control.

Findings

Low-rank dynamics identified in symmetric flow components.

Actuator pulses cause large impulsive flow perturbations.

Shock cell contraction observed during transient evolution.

Abstract

We investigate the forcing-induced transient between statistically stationary and cyclostationary states. The transient dynamics of a turbulent supersonic twin-rectangular jet flow, forced symmetrically at a Strouhal number of 0.9, are studied using synchronized large-eddy simulations (LES) and space-time proper orthogonal decomposition (space-time POD). Under plasma-actuated control, the statistically stationary jet evolves towards a cyclostationary state over a transient phase. Forcing-induced perturbations of the natural jet are extracted using synchronized simulations of the natural and forced jets. A database is collected that captures an ensemble of realizations of the perturbations within the initial transient. The spatiotemporal dynamics and statistics of the transient are analyzed using space-time POD for each symmetry component. The eigenvalue spectra unveil low-rank dynamics in the symmetric component. The spatial and temporal structures of the leading modes indicate that the initial pulse of the actuators produces large, impulsive perturbations to the flow field. The symmetric mode reveals the contraction of the shock cells due to the forcing, and shows the evolution of the mean flow deformation transient.