The Effect of Roll Rate on Simulated Entry Vehicle Ballistic Range Tests

Free-flight computational fluid/rigid-body dynamics simulations are now being explored as a way to augment physical experiments for characterizing the dynamic behavior of blunt-body atmospheric entry vehicles. Initializing these simulations with accurate initial conditions is critical to achieving validation against experimental results and characterizing vehicle behavior. This paper explores the impact of a nonnegligible initial roll rate on numerical free-flight simulations of ballistic range tests using the FUN3D Navier–Stokes flow solver and POST2 trajectory propagator. These ballistic range shots were performed on a model of the Supersonic Inflatable Aerodynamic Decelerator at the NASA Ames Hypervelocity Free-Flight Aerodynamics Facility. In the absence of measured roll data, a method for reconstructing the initial roll rate is developed assuming that a nonnegligible roll rate accounts for the exchange in amplitude between the experimental pitch and yaw data. Simulations of three shots spanning a range of initial roll rates are executed to evaluate the new method. Results are validated against the physical ballistic range tests. Simulations with the reconstructed roll rate are more accurate to the experimental data than those assuming a negligible initial roll rate. Direct calculation of the pitch damping coefficient also captures the effect of roll rate on pitching moment.