Multi-Species Effects for Plume Modeling on Launch Vehicle Systems

Abstract

A number of Reynold-Averaged Navier-Stokes (RANS) based Computational Fluid Dynamic (CFD) solutions are presented which detail the effect of various thermo-chemical models on plume simulations. Four different levels of thermo-chemical models are considered, each with increasing complexity. In the simplest case, plumes are modeled with a single "perfect air" simulant gas that is calorically perfect. The second model uses a single "equivalent" exhaust specie that is calorically perfect, but with molecular weight and frozen specific heats that mimic the mass-averaged nozzle exit conditions. The third model utilizes the same equivalent exhaust specie, but considers caloric imperfections. Finally, a full multispecie model with finite-rate chemistry and general thermodynamics is considered. Comparisons are made between the different levels of modeling for power-on simulations involving the Ares I launch vehicle. Generating power-on aerodynamic databases with CFD presents a tremendous challenge in terms of computational resources and time. As a result, launch vehicle designers would like to use the simplest, least expensive models that provide adequate results. This paper addresses some of the issues that arise when approximate models are utilized for plume simulations, and develops guidelines for when each model is appropriate.

USM3D Analysis of Roll-Control System Jet Effects on Ares Launch Vehicles

“…The temperature effect might have affected heat transfer but not the forces and moments that were the main objectives of this study. Results from [16] indicate minimal impacts on forces and moments between an ideal gas (calorically perfect air) approach and a higher-fidelity (calorically imperfect exhaust) approach for the Ares I-X RoCS. Finally, the ideal gas solution matched density and pressure at the thruster nozzle exit.…”

“…The single comparison of an ideal gas solution to a real gas solution was not expected to validate the use of the ideal gas model but to determine whether the ideal gas model missed any obvious flow phenomenon. The Loci-CHEM [16,17] CFD flow solver can compute chemically reacting mixtures of thermally perfect gases on three-dimensional, mixed-element unstructured meshes. Loci-CHEM is a finite-volume N-S flow solver with a finite rate and equilibrium chemistry.…”

“…A real gas approximation was used because a full-chemistry model would have been extremely expensive for modeling the RoCS thrusters [16]. The method of approximation followed the fundamental principles of thermodynamics for a mixture of thermally perfect gases.…”

Aero-Propulsive Characterization of a Flight Vehicle with Two Side-Jets

“…Since, the focus of the present study is mainly on obtaining accurate aerodynamic forces and moments, the gas-dynamic properties are assumed as calorically perfect. For modeling the mixing of air and jet plume with different set of gas thermal properties, the simplest air-plume-jet mixing methodology 'Calorically Perfect Equivalent Specie' model (CPES) [26] is used. An additional equation for conservation of specie-mass for obtaining the specie density is considered and hence the mass fraction of 'equivalent specie' is solved.…”

Multispecies Effects for Plume Modeling on Launch Vehicle Systems

“…Often the exit conditions are given by axisymmetric profiles of the species mass fractions and flow quantities at the nozzle exit in terms of radial distance from the centerline, i.e., exit r, u exit r, v exit r, and p exit r, from a quasi-1D reacting nozzle code [7]. Mass-averaged quantities at the exit were determined via integration in cylindrical coordinates [8]. The mass-averaged exit mixture values for the ratio of specific heats and molecular weight, exit andM exit , were assumed frozen for this specific calculation.…”