DSMC CHEMISTRY MODELLING AROUND A SPACECRAFT

Abstract

Hypersonic flows are characterized by the formation of discontinuous shock layer of extremely high temperatures. So gas in the hypersonic regime can be reacting and there could be exchange of energy between the different states of molecules. Since in rarefied gas flow density of gases is very low and non equilibrium conditions will arise. It is very difficult to accommodate the non equilibrium conditions, very few models have been developed to solve this complex flow problem. DSMC method, a particle based probabilistic method, is most accurate method to capture the non equilibrium and real gas effects in rarefied gas flow dynamics. Main objective of our dissertation is to develop a DSMC Q-K model for the rarefied gases of Martian atmosphere. The developed code is firstly verified by comparing the vibrational relaxation of carbon monoxide with existing model of oxygen molecule. Using the DSMC method, Composition of species of homogenous gas model at different equilibrium temperatures is calculated. A chemFoam chemistry solver is also used to calculate the mixture composition of same gas model at the same atmospheric conditions. The results of both the models are compared. To test the practice scenario a hypersonic one dimensional flow application in Martian atmosphere is studied using the DSMC model. Structure of shockwave, maximum translational peak temperature, distance of shock layer along the stagnation line, chemical phenomenon like dissociation, recombination and exchange of energy between different states of molecule and density ration in shockwave region is studied. Temperature profile around a plane shock structure for the Mars and Earth atmosphere is compared.