Multistable vortex patterns on slender, circular bodies at high incidence

Abstract

A rigidly supported tangent ogive model has been tested in low turbulent, incompressible flow at incidences of 35, 45, and 55 deg. A constant streamwise Reynolds number of 1.5 x 105 was maintained that produced laminar boundary-layer separation. Both unsteady pressures and flowfield velocities were measured, the latter with a three component laser Doppler velocimeter. Analysis of the results indicates that the vortex pattern may be unsteady at times, but that the flowfield can be idealized as steady and that variations in the measured side force are principally a result of changes in the mean vortex pattern. Large side forces are shown to be induced by flow fields that shed a major part of the first vortex. A relationship is established between side force magnitude and surface pressure fluctuations. The repeatability of side force measurements is examined and tests featuring high side force levels are found to be the most reproducible. Tests on a blunted model produced a decrease in side force and body vortices that were located a greater distance from the model surface. Comparison of current results with those from other studies suggests that a unique flowfield is associated with each side force value. In the incidence range of 45-55 deg, peak local force values from different sources are also in good agreement.