A computational capability has been developed for predicting the flowfield about projectiles, including the recirculatory base flow at transonic speeds. In addition, the developed code allows mass injection at the projectile base and hence is used to show the effects of base bleed on base drag. Computations have been made for a secant-ogive-cylinder projectile for a series of Mach numbers in the transonic flow regime. Computed results show the qualitative and quantitative nature of base flow with and without base bleed. Base drag is computed and compared with the experimental data and semiempirical predictions. The reduction in base drag with base bleed is clearly predicted for various mass injection rates. Results are also presented that show the variation of total aerodynamic drag both with and without mass injection for Mach numbers of 0.9 < M< 1.2. The results obtained indicate that, with further development, this computational technique may provide useful design guidance for projectiles.

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The ability to predict the complete set of aerodynamic performance parameters for projectile configurations is the goal of the computational aerodynamicists at the U.S. Army Research Laboratory. To achieve this goal, predictive capabilities that use Navier-Stokes computational techniques have been developed and applied to an extensive number of projectile configurations. A summary of code validation efforts and applications for both spin-stabilized and fin-stabilized projectile configurations are described. Significant progress in the predictive capability for projectile aerodynamics has been achieved through the availability of substantial supercomputer resources and modern computational techniques. Current and future research areas of interest are described and provide an indication of computer resources and code enhancements needed to continue the progress in projectile computational aerodynamics. NomenclatureMagnus (side) force coefficient D =reference diameter of model, m d = local diameter of model, m / =mass injection parameter, / L =length, m M =Mach number m =mass flow rate of injected gas p/w/A, P =pressure normalized by p^2 (also spin rate, rad/s) PD/V =nondimensional spin rate Re = Reynolds number T = temperature, K u = velocity component in the x direction, m/s V =freestream velocity, m/s v = velocity component in the y direction, m/s x,y,z -Cartesian coordinates a = angle of attack, deg p = density, normalized by pĈ D = axial spin rate, rad/s

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