TECHNIQUES FOR SOLVING NONEQUILIBRIUM EXPANDING FLOW PROBLEMS.
CORNELL AERONAUTICAL LAB INC BUFFALO N Y
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Methods of solving the problem of expanding nonequilibrium flows have been under development at CAL for some time. The extension of the calculations to higher temperatures and pressures has necessitated improvements in the calculation methods. This report summarizes those techniques used at CAL which have not been previously discussed and includes the recent modifications. Numerical solutions for nonequilibrium expansions of high enthalpy airflows are presented in AD-610 820. The solution of nonequilibrium nozzle flows involves the numerical integration of a set of nonlinear ordinary differential equations. Difficulties are encountered in starting the solution since the flow is initially in equilibrium. The starting technique used at CAL is based on a perturbation about the equilibrium solution. Several possible perturbation methods are discussed and compared. A method is presented for mixing the equilibrium and nonequilibrium equations which is useful for systems involving widely different reaction rates. Improvements in the numerical integration technique, including the application of a recent modification of the Runge-Kutta method, are discussed. These improvements reduce oscillations in the solutions and reduce computing time. It is shown that substantial reductions in computing time are made possible by starting the solution as far downstream as possible. The solutions obtained do not depend on the starting point. Author