Highly dilute gas flows over an ellipse

This paper presents recent investigation results on free molecular flows over a diffusely or specularly reflective ellipse, by using the gaskinetic theory. A virtual density distribution along the diffusely reflective surface is introduced to aid the investigations. Many local surface properties are obtained, including the surface slip velocity and coefficients for pressure, friction, and heat flux. Global coefficients for aerodynamic forces and moments and mass center–force center distances are also obtained by integrating the local surface distributions. In the end, analytical expressions for the flowfields around a diffusely or specularly reflective ellipse are also obtained. Special non-dimensional parameters, such as temperature and speed ratios, are explicitly embedded in these expressions. Particle simulations with the direct simulation Monte Carlo (DSMC) method are performed to validate the above results. Those expressions need computers for evaluations; however, the cost is very minor when compared with DSMC simulations. The approaches are heuristic to investigate other external collisionless flows, and the load coefficients can be considered as baseline references at the high Knudsen number limit. By using these collisionless flow results, it is feasible to further study less rarefied gas flows over an ellipse, for example, with an asymptotic method. Swift parameter studies based on these solutions can be performed to study their effect.