Theoretical and Numerical Investigation of Nonlinear Thermoacoustic, Acoustic, and Detonation Waves

TL;DR

This paper combines theoretical and numerical methods to analyze nonlinear thermoacoustic, acoustic, and detonation waves, focusing on spectral energy dynamics, instability, shock formation, and complex geometries.

Contribution

It develops a second-order governing system and energy analysis for nonlinear waves, extending to thermoacoustic instability and detonation wave simulations.

Findings

Spectral energy cascade characterized in nonlinear acoustic waves.

Thermoacoustic instability leads to shock wave generation.

Detonation waves modeled using low-order simulations.

Abstract

We begin with the theoretical study of spectral energy cascade due to the propagation of high amplitude sound in the absence of thermal sources. To this end, a first-principles-based system of governing equations, correct up to second order in perturbation variables is derived. The exact energy corollary of such second-order system of equations is then formulated and used to elucidate the spectral energy dynamics of nonlinear acoustic waves. We then extend this analysis to thermoacoustically unstable waves -- i.e. amplified as a result of thermoacoustic instability. We drive such instability up until the generation of shock waves. We further study the nonlinear wave propagation in geometrically complex case of waves induced by the spark plasma between the electrodes. This case adds the geometrical complexity of a curved, three-dimensional shock, yielding vorticity production due to baroclinic torque. Finally, detonation waves are simulated by using a low-order approach, in a periodic setup subjected to high pressure inlet and exhaust of combustible gaseous mixture. An order adaptive fully compressible and unstructured Navier Stokes solver is currently under development to enable higher fidelity studies of both the spark plasma and detonation wave problem in the future.