Resolving Nonequilibrium Gas Kinetics in Supersonic Neutral Flows with Coherent Rayleigh Brillouin Scattering

TL;DR

This paper demonstrates the use of single-shot coherent Rayleigh-Brillouin scattering to characterize nonequilibrium supersonic gas flows, revealing detailed velocity and density distributions and deviations from equilibrium.

Contribution

It introduces a novel application of CRBS for high-resolution, single-shot measurements of complex, unsteady supersonic flows, validated against numerical simulations.

Findings

Single-shot spectra show significant deviations from Maxwellian distributions.

CRBS effectively maps velocity, density, and gradients in supersonic jets.

Good agreement between measurements and simulations.

Abstract

We present a characterization of high-speed flows in nonequilibrium thermodynamic conditions using single-shot coherent Rayleigh-Brillouin scattering(CRBS). The technique is applied on a highly underexpanded jet using 200ns laser pulses, enabling simultaneous probing of multiple spatial locations. We map the jets average axial velocity and density distributions and resolve local velocity gradients, providing access to parameters relevant to turbulence characterization. The measurements are validated against numerical simulations, showing good agreement overall. We find that in most cases individual single-shot spectra exhibit substantial deviation from the bulk averaged lineshapes, reflecting the non-Maxwellian velocity distributions generated by shock-induced regimes. The results presented here establish single-shot CRBS as an important tool for direct measurements of flow velocity components, velocity gradients, and density in complex, unsteady supersonic environments.