Experimental investigation of influence of strake wings on self-induced roll motion at high angles of attack

The modern high performance air vehicles are required to have extreme maneuverability, which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the self-induced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at α = 60°. The free-to-roll results show that the model with whole strake wings (baseline), the model assembled with three strake wings (Case A) and the model assembled with two opposite strake wings (Case C) experience the spinning, while the model assembled with two adjacent strake wings (Case B), the model assembled with one strake wing (Case D) and the model with no strake wing (Case E) trim or slightly vibrate at a certain “×” rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at α = 60°.