A new LU-SGS flow solver for calculating reentry flows

In this dissertation, an LU-SGS flow solver is developed and evaluated. The LU-SGS method of Yoon is adapted to calculate axisymmetric, chemically reacting and weakly ionized flowfields characteristic of reentry vehicles. Modifications are presented that improve the numerical efficiency and stability of the LU-SGS scheme for the calculation of nonequilibrium reacting flows. A parallel effort is made to improve the physical modelling of the flowfield. A new two-temperature dissociation model is derived from kinetic theory to account for the coupled vibration-dissociation process. The model minimizes uncertainties associated with the Park two-temperature model. The effects of the model on AOTV type flowfields are examined.; The accuracy of the continuum equations employed in this study are examined by comparing with numerical flow solutions generated using the Direct Simulation Monte Carlo (DSMC) method. For this comparison, a four temperature thermal model is employed that allows the calculation of separate translational, rotational, vibrational and electron-electronic temperatures. Calculations were made for flows with and without ionization over the Project Fire II vehicle. For the Project Fire II conditions considered (76 km and above), assuming the translational temperature equal to rotational temperature and the vibrational temperature equal to the electron-electronic temperature were found to be poor approximations.; Surface convective heat transfer for a number of Fire II flow calculations are compared. The trends of the Fire II experimental data were predicted and the present numerical results compared well with solutions from other Computational Fluid Dynamic (CFD) codes and the DSMC method. The effects of a number of flow phenomena on the convective surface heating are examined. For the fire II conditions considered, the flow was almost fully dissociated. As a result, the recombination of Nitrogen was found to have the most influence on the surface heating rates. Other phenomena such as changing the thermal model, transport model, number of species and chemical rates had little effect on the surface convective heat transfer rates.; Finally, the computational efficiency of the present method is compared to the Gauss-Siedel line relaxation method of Candler. CPU costs for each method are calculated for inviscid and viscous flows in thermal and chemical nonequilibrium over a cylinder. Total CPU costs for the methods were found to be comparable for the inviscid calculation. However, the Gauss-Siedel method was found to be much faster than the present LU-SGS scheme for viscous flow calculations.