Unsteady Skin-Friction Measurements on a Maneuvering

The skin-friction magnitude was measured for steady and unsteady flow over a Suboff submarine model by surface hot-film constant temperature sensors. the locations of the local spatial minima in the skin-friction magnitudes are used to obtain the separation locations. Steady surface static pressures were measured at 100 and 200 angles of attack. the dynamic plunge-pitch-roll model mount (DyPPiR) in the Stability Wind Tunnel was used to simulate rapid pitch-up maneuvers, which are a linear ramp from 10 to 27 deg in 0.33 seconds, for the bare-body and sail-on-side cases at Re(t)=5.5 x 1,000,000. Steady results show a cross-flow separation structure on the leeward side of the bare-body. in the sail-on-side case, the separation pattern of the non-sail region follows the bare-body separation trends; on the sail side it is strongly affected by the presence of the sail-body junction and its horseshoe-vortex type separation. Unsteady results of the bare-body and the non-sail region of the sail-on-side case show a different separation topology from the steady flow separation structure and significant time lags, which are described by a first-order time lag model. the unsteady separation pattern of the sail side does not follow the quasi-steady data with a time lag.