An experimental investigation of the physical mechanisms controlling the asymmetric flow past slender bodies at large angles of attack

An experimental investigation of the effects of geometric perturbations on the asymmetric flow past slender bodies has been conducted. The perturbations included variations in model tip sharpness, roughness and shape as well as discrete surface perturbations represented by beads of varying height and diameter attached to the model surface. Two cone/cylinder models having 9 and 10 deg semi-apex angles and a 3.0 caliber tangent ogive model, all having base diameters of 3.5 in were tested at laminar flow conditions at angles of attack from 30 to 60 deg. Data were taken with each model from 3 circumferential rows of pressure taps at a flow speed of 45 ft/s corresponding to a Reynolds number of 8.4 x 10{dollar}sp4{dollar} based on model base diameter. Also, a helium bubble flow visualization technique was used at a speed of 15 ft/s corresponding to a Reynolds number of 2.5 x 10{dollar}sp4{dollar}. Beads were tested by placing the model at a roll position having either a symmetric or a highly asymmetric flowfield, and then attaching a bead to the model surface at varying axial and circumferential positions. Bead effectiveness was judged by the extent to which the flowfield was affected. Data showed the beads to be very effective when placed approximately 140 deg from the windward ray, and to decrease in effectiveness with decreasing bead size and distance from the tip. The data showed no significant change in this behavior with variations in angle of attack and tip bluntness. Tests without beads, conducted with sets of tips manufactured to identical specifications, showed the behavior of sectional side-force with roll position to be a function of machining imperfections and surface roughness. Filing model tips such that the apex was elliptical in cross-section changed the variation of the flowfields with model roll position from random to regular and predictable. A rotatable elliptical tip was able to produce a large or small side-force condition (asymmetric or symmetric flowfield) irrespective of the model position and attitude. Data showed this device to have promise as an aid to wind-tunnel testing and as a high-angle-of-attack yaw-control device for aircraft.