EXACT AND APPROXIMATE RIEMANN SOLVERS FOR REAL GASES

A procedure is developed for solving the Riemann problem (RP) for the flow of gases obeying an equation of state (EOS) of the form p = p(rho , T). A first method is introduced, producing solutions of the exact R P; the algorithm is validated by applying it to the classical test cas e of the shock-tube, for a perfect gas. Thereafter, the method is appl ied to gases having EOS of the Van der Waals or virial types, with ver y good resulting accuracy; however, the procedure is somewhat demandin g in computer time. Therefore, some simplifying assumptions are introd uced into the computation of simple waves, leading to an approximate s olution of the RP; in most circumstances, excellent results are obtain ed, and the computer time is much more competitive. However, under cer tain extreme flow conditions, it is recommended that a combination of the exact and approximate solvers for the RP be employed. (C) 1994 Aca demic Press, Inc.