Projectile aerodynamics: Measurement and computation

An experimental study has been performed at M∞=8.2 and Re∞/cm=93000 to examine:

1. The effect of strakes on the aerodynamic characteristics and performance on slender elliptic cone missile configurations. Some information regarding the shock layer was obtained from schlieren pictures. Detailed flow properties in the shock layer were obtained, for some elliptic cone configurations with and without strakes, using a threedimensional, high resolution, iterative, finite volume parabolized Navier-Stokes solver. Surface flow visualisation, using an oil-dot technique, and pressure measurements were made on one of the models to determine the effect of strakes. Lift, drag and pitching moment characteristics for the elliptic cones with and without strakes were obtained using a three component strain-gauge balance. No gross external flow differences were detected from the schlieren pictures for models tested due to the addition of strakes. Oil-dot visualisation demonstrates that the strakes alter the surface flow characteristics and tended to inhibit the cross-flow. The addition of strakes caused a reduction of pressure on the leeward side and an increase of pressure on the windward side. The strakes produced a significant increase in the lift and drag coefficients, in the incidence range of 0° to 200. The right elliptic cone without strakes with its major axis horizontal exhibits higher lift coefficients than the cone with its major axis vertical. The numerical study predicted the complex flowfield surrounding the right elliptic cone with its major axis horizontal, gave a better understanding of the complicated nature of the flow and good indications of the shock shape and vortex core positions. An estimation model of the aerodynamic forces and moments for the right elliptic cone with and without strakes was developed based on the standard Newtonian theory. The model successfully predicted the experimental trends in the aerodynamic coefficients.
2. The aerodynamic effectiveness of a cylinder flare body at zero incidence under laminar and turbulent boundary layer conditions. Two nose geometries, namely a 10° half-angle sharp cone and a hemisphere, were used. The surface flow over the cylinderflare body was studied using oil-dot and liquid crystal techniques. Some information regarding the shock layer was obtained from schlieren pictures. The effects of entropy layer and boundary layer state on flare effectiveness were deduced from pressure measurements over the cylinder and the flare. The most important difference between the laminar and turbulent boundary layer interaction is that a much smaller angle is necessary to cause laminar separation than that necessary for turbulent separation. The determination of incipient separation is very sensitive to the detection method employed. The existence of a small scale separation bubble can explain the differences in the determination of incipient separation angles if different experimental methods are used. The addition of a hemisphere nose reduces the surface pressure and heat transfer levels on the flare. This is due to loss of reservoir pressure across the bow shock wave. The reduction of flare pressure also reduces the separated flow lengths for the laminar case, whereas for the turbulent case the separated flow lengths are increased. This may be due to the boundary layer along the cylinder body not being fully developed. The effect of Mach shear on the flare pressures distribution has been calculated theoretically. The model predicted the experimental results satisfactorily.