Subsonic Aerodynamic Evaluation of Heat Shield Roughness Effects on the SpaceX Dragon Crew Capsule

摘要

An experimental subsonic aerodynamic investigation of heat shield roughness effects for the Space Exploration Technologies Corporation's (SpaceX) Dragon Crew Capsule was accomplished. Two models of the Dragon were evaluated. One model had a smooth heat shield, simulating the Dragon's performance in a launch abort scenario. The second model simulated an ablated heat shield that would form upon re-entry through earth's atmosphere by using #80 grit sand bonded to the heat shield. Both models were fitted with pressure ports which collected pressure data on the Dragon's heat shield, shoulder, and backshell. The models were tested through an angle of attack sweep at eighteen roll angles. The resulting pressure data were mapped on a 3-Dimensional, 360° grid, and post-processing software was used to qualitatively display the data. The purpose of the investigation was to analyze the differences between the pressure distribution of the rough and smooth heat shields in the subsonic, compressible regime. The results showed noticeable differences between the models' shoulder pressures especially at high angles of attack. The rough heat shield model exhibited higher surface pressures across its shoulder at high angles of attack. The data provide evidence that a higher adverse pressure gradient across the shoulder of the rough heat shield model likely caused earlier separation. The rough and smooth heat shield models of the Dragon were also wind tunnel tested to collect force and moment data. These data complemented the surface pressure analysis by providing good correlation to the surface pressure distribution data. The force and moment testing revealed that the rough heat shield had a reduced C_(Mα) of 5.6% at low angles of attack compared to the smooth heat shield model. Another result of the force and moment testing showed that based on L/D differences, the smooth heat shield configuration had a cross-range capability 5.69% greater than that of the rough heat shield configuration. Furthermore, the experimental surface pressure of the Dragon capsule with a smooth heat shield was compared to previous Computational Fluid Dynamic (CFD) solutions. The experimental pressure data matched CFD solutions closely but with slight differences around the capsule shoulder. Data from this investigation will be important in the design of launch abort and re-entry flight profiles and provide direct input to the National Aeronautics and Space Administration (NASA) in the certification of SpaceX's Dragon Crew Capsule.