Longitudinal Aerodynamic Performance of the Apollo Entry Capsule near Transonic Speeds

摘要

A complex dynamic behavior exists in the flow structures surrounding blunt atmospheric entry capsules as they decelerate from supersonic to subsonic speeds during a lifting reentry. In the current study, unsteady simulations of the Apollo capsule undergoing pitch oscillations were carried out applying the DLR (German Aerospace Center) TAU code to predict the static and dynamic aerodynamic derivatives. Numerical results for static analysis show that the capsule, with its given center of gravity, is predicted to be statically stable both in the super- and subsonic regimes. The dynamic analysis was then performed, indicating that the capsule will turn dynamically unstable when the trim angle of attack is close to zero or if the freestream Mach number decreases. The unsteadiness of wake vortices and the influence of wake pressure on the moment coefficient appear to be the primary factors affecting the dynamic behavior. A time lag between the capsule oscillations and the moments acting on the backcone is shown to be the source of the observed dynamic instabilities.