EFFECT OF GEOMETRICAL DISTURBANCE ON VORTEX ASYMMETRY

The phenomena of the flow about a slender body of revolution placed at incidence to an oncoming stream were numerically investigated for angles of attack of 20 and 40 deg and a Reynolds number of 2 x 10(5) based on maximum body diameter. At angle of attack of 20 deg, the flow was steady and symmetric, and the presence of a perturbation, which was placed near the tip of the body, made only a small change. At angle of attack of 40 deg, the flow was found to be steady (except for a small-amplitude, high-frequency unsteadiness of the shear layer), but became highly asymmetric when a space-fixed, time-invariant disturbance was added near the tip. The level of the asymmetry was dependent on the size and location of the disturbance. When the disturbance was removed, the flowfield relaxed to its original symmetric shape. On the basis of this observation, experimental data, and other theoretical indicators, it is suggested that the origin of the asymmetry is a convective-type instability of the originally symmetric flow.