Numerical Prediction of Internal Supersonic Flow in a Regulation Valve for Low-Thrust Space Engines

This work deals with the numerical prediction of the unsteady flow field developing in a regulation valve for space thrusters. The flow field displays an unsteady behavior characterized by complex flow patterns, because such valves have a very narrow throat and because of the presence of geometrical slope discontinuities downstream the throat for design constraints. The narrowness of the throat induces strong flow accelerations and therefore strong temperature and pressure reductions. The geometrical discontinuities cause the occurrence of local flow separations and shock waves, with an high degree of unsteadiness. Experiments have pointed out how the degree of unsteadiness strongly depends upon the nature of the gas feeding the valve. The strongest unsteadiness has been observed in the case of xenon at low exit pressures. Numerical simulations, using a compressible Navier-Stokes flow solver, have been performed under different working conditions and for two different gases, nitrogen and xenon. The results agree with experiments, and provide details of the unsteadiness mechanism and of its evolution depending upon the operating conditions.