THE REDUCTION OF NUMERICAL ENTROPY GENERATED BY UNSTEADY SHOCKWAVES

The computation of slowly moving shockwaves is considered. A numerical error is introduced into the solution during an explicit computation, which results in the generation of spurious entropy. The generation o f this spurious entropy and its effect on the pressure wave in Euler f lows is examined, in one dimension by considering a moving shock in a constant area duct, and in two dimensions by considering an unsteady a erofoil how. An efficient temporal discretisation is presented, whose advantages over the explicit scheme are two-fold. First, the numerical entropy generation due to shock motion is eliminated, and second, the CPU requirements for a two-dimensional unsteady computation are reduc ed by a factor of five from that required for the explicit scheme, for no loss of accuracy.