Experimental investigations of the initial growth of flow asymmetries over a slender body of revolution at high angles of attack

This paper describes an experimental investigation of the initial growth of flow asymmetries over a slender body of revolution at high angles of attack with natural and disturbed noses. Time-resolved particle image velocimetry was used to investigate the flow field around the body. The experimental results show that initially different amplitudes of unsteady disturbances near the tip are established owing to the tip imperfections. These unsteady disturbances experience a super-exponential growth near the tip and continue to grow exponentially due to linear instabilities. Attachment of a piece to the tip brings a larger initial difference and extends the super-exponential growth region. Thus, the disturbance amplitudes and their differences are larger for the disturbed case than for the natural case before reaching the neutral point of linear instability. The amplified disturbances lead to different instability vortex strengths in the separated shear layers, which feed continuously into the two primary concentrated vortices. As a result, the primary vortex strengths differ, which result in the initial vortex asymmetry. The experiment results demonstrate that the initial flow asymmetry arises from an asymmetric development of the boundary layer instability.