Global Stability Analysis of ICP Plasma Jets Using Equilibrium and Non-Equilibrium Fluid Models

Inductively coupled plasma (ICP) wind tunnel facilities play a key role in the development of Thermal Protection Systems (TPS) for high-speed flight systems. ICP-generated thermal plasma jets exhibit a variety of complex dynamics across the ICP operating range, influencing the flow field impinging on a TPS sample and complicating inferences from flow field diagnostics. We present advances towards the prediction of the dynamic behavior of ICP-generated plasma jets using global linear stability analysis. Due to the high temperatures in the flow field, it is necessary to account for chemical reactions. If the chemical reactions happen fast enough, the fluid can be assumed to be in chemical and thermodynamic equilibrium. Under high-power, low-pressure operating conditions, the fluid time scale is comparable to the time scale of the chemical reactions, and it becomes crucial to model the finite-rate chemical reactions happening in the thermal plasma jet. Therefore, two fluid models -- Local Thermodynamic Equilibrium (LTE) and Non-Local Thermodynamic Equilibrium (NLTE) -- are used to compute the base state and perform linear analysis. The current framework is verified by comparing the results against an LTE extension of the inviscid Rayleigh equation. The effect of the fluid model on the global mode spectra and eigenfunctions is discussed.