Transport dynamics of an ellipsoidal particle in free molecular gas flow regime

Abstract

Translational and rotational dynamics of a transporting particle in the free molecular gas flow regime are investigated using an in-house, multi-species, three dimensional Direct Simulation Monte Carlo (DSMC) solver. The DSMC algorithm is modified to study free molecular gas flows and validated against the analytical results for the dynamics of a spherical particle. A particular focus of this work is on estimating the effects of particle size, shape, and orientation on the dynamics of an ellipsoidal particle in free molecular gas and comparing them with that of a spherical particle. Properties such as particle speed, temperature, drag, and heat transfer coefficients are considered for comparison. The effect of particle shape on the aforesaid properties is qualitatively discussed and quantified through a comprehensive analysis taking care of lift, pitching moment, particle rotation, and the associated resistive torque. The relaxation of an ellipsoidal particle to surrounding gas conditions is simulated at zero and non-zero angles of attack to demonstrate the effect of particle orientation. Furthermore, the particle size effect on its translational and rotational dynamics is discussed. Finally, the trajectory of a spherical particle is compared with that of an ellipsoidal particle at different eccentricities.