APPLICATION OF METHOD OF CHARACTERISTICS TO UNDEREXPANDED, FREEJET FLOWS WITH VIBRATIONAL NONEQUILIBRIUM

The method of characteristics (MOC) is employed computationally in the simulation of planar or axisymmetric, steady, supersonic flows in hig hly underexpanded freejets, The gas is assumed to be inviscid and nonr eacting but may be vibrationally frozen, relaxing, or equilibrated. Th e ordinary differential equations obtained by the MOC are integrated a long the characteristics by a combined second-order, explicit-first-or der, implicit method in regions of the flow with relatively rapid vibr ational energy transfer (VET) and by a fully second-order, explicit me thod in regions with either slow or. very rapid VET. Results from MOC simulations of flows with constant specific-heat ratios are verified b y comparison with results obtained in previous MOC computations of exp ansion-fan flows and with empirically based correlations giving the si ze of the barrel-shock structure as a function of stagnation-to-ambien t-pressure ratio, Comparisons are also made between MOC results for a vibrationally relaxing gas and results for vibrationally frozen and eq uilibrated gases, to verify the computational methods used to simulate flows with VET. The demonstrated capability for simulating underexpan ded freejet flowfields represents a useful tool for predicting the res ults of experiments conducted in a small-scale shock-tunnel facility.