DIRECT SIMULATION WITH VIBRATION-DISSOCIATION COUPLING

In the investigation of hypersonic rarefied flows, it is important to consider the effects of thermal nonequilibrium on the dissociation rat es. Because the vibrational mode requires a finite time to relax, vibr ational energy may not be available for dissociation immediately behin d the shock. In this way, the dissociation of the preshock species can be delayed for a significant portion of the hypersonic shock layer. T he majority of implementations of the direct simulation Monte Carlo (D SMC) method of Bird do not account for vibration-dissociation coupling . Haas and Boyd have proposed the vibrationally favored dissociation ( VFD) model to accomplish this task. Their model made use of measuremen ts of induction distance to determine model constants. A more general expression has been derived that does not require any experimental inp ut. The model is used to calculate one-dimensional shock waves in nitr ogen and the flow past a lunar transfer vehicle (1,TV). For the condit ions considered in the simulation, the influence of vibration-dissocia tion coupling on heat transfer in the stagnation region of the LTV can be important.