Static Instability of Martian Entering Vehicles at Small Angle of Attack

Martian atmosphere which is quite different from Earth atmosphere brings a new challenge for computational fluid dynamics in aerodynamic prediction of Mars entry vehicles. Three-dimensional Navier-Stokes equations with high temperature gas model and perfect gas model have been solved by a parallel code, aiming at entry process of Mars Pathfinder. Aerodynamic characteristics has been calculated and analyzed, discussion about mechanism of static instability at small angle of attack found in simulation has been carried out. The results shows that good agreement is achieved among the numerical results, the reference values and the flight data of Viking, which validates the physical chemical models and the numerical methods applied in this paper. Prediction and comparison of aerodynamic characteristics of MPF prove results of high temperature gas model are close to LAURA code. Perfect gas model with effective specific heat ratio is capable of computing the lift and drag coefficients. At 2 degree angle of attack, MPF exhibits static instability along the trajectory, which perfect gas model failed to catch on. It is concluded that sonic line shifting around the shoulder in windward and subsonic region changing in leeward, result in different transportation processes of pressure from the expansion zone behind the shoulder to upstream, which is the main reason of occurrence of static instability.