3-DIMENSIONAL FLOW CALCULATIONS FOR A PROJECTILE WITH STANDARD AND DOME BASES

Test firings of the 155-mm XM825 artillery projectile have shown that its night performance was affected by configurational changes to the b ase cavity. This was an unexpected result, and a clear understanding o f why these changes affected the flight behavior did not exist. A comp utational study has been made for the two different base-cavity config urations which were night tested. Flowfield computations have been per formed at 0.8<M<1.5 and alpha = 4.0 deg using a recently developed thr ee-dimensional Navier-Stokes code. The computed results show the quali tative features of the base region flowfield for the two base cavities . The base changes are found to alter the recirculation patterns in th e wake, which in turn affect the expansion at the base corner. These c hanges in the flow structure contribute to small changes in the base p ressure. Aerodynamic force and moment coefficients have been obtained from the computed pressures and are presented as a function of Mach nu mber. Computed results show small differences in normal force and pitc hing moment coefficients similar to that found in the range data.