Prediction of Unsteady Aerodynamic Forces on Maneuvering Delta Wings

A semi-empirical model was developed to study the breakdown effects on maneuvering delta wings performing very high angle of attack excursions. The basic vortical flow model used was the Brown & Michael model and an unsteady source distribution was found to simulate the breakdown of the leading edge vortices. The source distribution is based on experimental observations of the vortex breakdown chordwise propagation during pitch-down and pitch-up motion. In spite of the simplicity of the vortical model used, the new model simulates the present complicated flow field. This model succeeds in predicting the leading edge core position hysteresis, the hysteresis in the unsteady pressure distribution and the corresponding airloads at extreme angles of attack. The normal force and pitching moment results are in good agreement with experimental measurements.