Vortex Dynamics of a Tangent Ogive at High Angle of Attack

Abstract

The flowfield around an axisymmetric forebody at a moderate angle of attack (40 o < � < 60 o ) can produce a significant side force as the result of an asymmetric pres- sure distribution around the body. The asymmetry of the pressure distribution results from a steady, asymmetric vortex configuration around the body even though the body is axisymmetric. Unsteady laminar simulations were performed on a von Karman tangent ogive forebody with a fineness ratio of 3.5, angle of attack of 50 degrees, and a diameter based Reynolds number of 220,000. As a first step towards feedback flow control of the asymmetric vortex state, open-loop disturbances similar to those produced by a Dielectric Barrier Discharge (DBD) plasma actuator near the tip of the model were simulated. The resulting side force from the open-loop simulations are compared to the unforced simu- lations. In the unforced case, a large side force was observed with maximum amplitudes similar to those observed in a companion experiment. However, the side force fluctuates between the port and starboard sides, in contrast to experimental observation where the side force is relatively steady. When forcing is turned on, the resultant asymmetric vortex state locks into one position where the magnitude of the side force is proportional to the strength of the applied forcing. These simulations, both forced and unforced, are used to develop a flow state database through Proper Orthogonal Decomposition (POD) for the development of reduced order models. It is shown that the second POD mode (including the mean) captures the asymmetry of the different vortex states tested.