Unsteady Crossflow Separation Location Measurements on a Maneuvering 6:1 Prolate Spheroid

Abstract

The crossflow separation of a 6:1 prolate spheroid undergoing transient maneuvers is studied. The dynamic plunge-pitch-roll model mount provides the unique capability to simulate unsteady maneuvers in a wind tunnel. Hot-film sensors are used with constant-temperature anemometers to measure the time-depcndent wall shear at points over the entire model surface. Minima in wall shear are used to indicate separation locations. Steady and unsteady data are presented for two fast maneuvers: a 0-30-deg, 0.33-s(t' = tU /L = 11) ramp pitchup about the model center (pitchup maneuver) and a 0-13.5-deg, 0.25-s (t' = 8.3) pitchup about the model center that simulates the time-dependent sideslip angle of a submarine entering a turning maneuver (submarine maneuver). Data show that, especially at higher angles of attack, significant lags occur in the flowfield during the maneuvers compared with the steady cases. In particular, separation is delayed at all locations of the model by up to a 10-deg higher angle of attack in the unsteady maneuvers compared with the steady data. Equivalently, the separation structure during the unsteady maneuvers lags the steady data by from 1.5 to 3.5 nondimensional time units t'