Prediction of the flowfield in laser propulsion devices

The difficulties encountered in modeling laser heating in a propulsive nozzle are discussed. Two basic formulations, an approximate low Mach number analysis or the complete Navier-Stokes equations, can be used. The former reduces to a single ordinary differential equation for which the mass flow is an eigenvalue. This representation has been considered by several researchers, but the precision with which the eigenvalue must be determined makes it impractical to obtain solutions for some values of the parameters. The present paper contains the first reported solutions to the complete Navier-Stokes equations for this problem. These results, which were obtained with an implicit time-marching method, no longer contain an eigenvalue, but the complex, rapidly developing physics in the flowfield prevent convergence in some regimes. Solutions for laser absorption in hydrogen-seedant mixtures demonstrate that the position of the heat absorption region is controlled by the incoming beam intensity while the mass flux is determined by the nozzle throat area. These two methods are related to each other by showing that the eigenvalue analysis is a rational approximation to the Navier-Stokes equations.