DSMC-CFD comparison of a high altitude, hypersonic reentry flow using the Mott-Smith model

Stardust reentry flows have been simulated at 80 km altitude, 12.8 km/s, using the direct simulation Monte Carlo (DSMC) and computational fluid dynamics (CFD). Neutral and ionization processes among neutral air species, as well as five ionic species and electrons were considered in the DSMC flowfleld modeling using the ion-averaged velocity model to maintain charge-neutrality. In CFD, two electron temperature models were compared, and it was found that the degree of ionization (DOI) is sensitive to the electron temperature model. At 80 km, the DOI predicted by DSMC was found to be approximately 3 %, but in CFD, the DOI is greater than 20 % for the case of T _e = T _tr and 9 % for the case of T _e = T _vib, Therefore, compared to the DSMC solution, the assumption of T _e = T _vib, is preferable in CFD. Using the Mott-Smith (M-S) model, good agreement was obtained between the analytical bimodal distribution functions and DSMC velocity distributions. An effective temperature correction in the relaxation and chemical reaction models using the M-S model was developed in CFD, and the model reduced the continuum breakdown discrepancy between DSMC and CFD inside the shock in terms of DOI and temperatures. With the M-S model, the DOI for the case of T _e = T _vib, in CFD is decreased by approximately 3%.