Analysis of Reacting Flowfields in LowThrust Rocket Engines and Plumes.
Abstract
The mixing and combustion processes in small gaseous hydrogenoxygen thrusters and plumes are studied by means of a computational model developed as a general purpose analytic procedure for solving low speed, reacting, internal flowfields. The model includes the full NavierStokes equations coupled with species diffusion equations for a hydrogenoxygen reaction kinetics system as well as the option to use either the kvarepsilon or qomega low Reynolds number, two equation turbulence models. Solution of the governing equations is accomplished by a finitevolume formulation with centraldifference spatial discretizations and an explicit, fourstage, Runge Kutta timeintegration procedure. The Runge Kutta scheme appears to provide efficient convergence when applied to the calculation of turbulent, reacting flowfields in these small thrusters. Appropriate boundary conditions are developed to properly model propellant mass flowrates and regenerative wall cooling. The computational method is validated against measured engine performance parameters on a global level, as well as experimentally obtained exit plane and plume flowfield properties on a local level. The model does an excellent job of predicting the measured performance trends of an auxiliary thruster as a function of O/F ratio, although the performance levels are consistently underpredicted by approximately 4%. These differences arise because the extent to which the wall coolant layer and combustion gases mix and react is underpredicted. Predictions of velocity components, temperature and species number densities in the nearfield plume regions of several low thrust engines show reasonable agreement with experimental data obtained by two separate laser diagnostic techniques. Discrepancies between the predictions and measurements are primarily due to threedimensional mixing processes which are not accounted for in the analysis. Both comparisons with experiment and the evident reason for errors in absolute levels of predicted quantities suggest the method should prove valuable for predicting parametric trends for design studies. In addition, issues such as numerical stability, robustness and computational efficiency are addressed. These include the evaluation of a numerically compatible twoequation turbulence model and the implementation of a timederivative preconditioning method for convergence enhancement of low Mach number, chemically reacting flows.
 Publication:

Ph.D. Thesis
 Pub Date:
 1992
 Bibcode:
 1992PhDT........55W
 Keywords:

 Engineering: Mechanical; Engineering: Aerospace; Physics: Fluid and Plasma;
 Combustible Flow;
 Finite Volume Method;
 Flow Distribution;
 Gaseous Rocket Propellants;
 Hydrogen Oxygen Engines;
 Low Thrust;
 NavierStokes Equation;
 Numerical Flow Visualization;
 Rocket Exhaust;
 RungeKutta Method;
 Turbulence Models;
 Turbulent Combustion;
 Turbulent Mixing;
 Computational Fluid Dynamics;
 KEpsilon Turbulence Model;
 Low Reynolds Number;
 Low Speed;
 Plumes;
 Reaction Kinetics;
 Species Diffusion;
 Wall Flow;
 Spacecraft Propulsion and Power