The Cannon-Projectile Blow-By Flow Field
ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER WATERVLIET NY BENET LABS
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The objective of this work was to document the numerical simulation of the cannon projectile blow-by flow for a Zone six firing of an M549A1 with XM230 charge. The steady, axisymmetric flow was determined by use of the NPARC Computational Fluid Dynamics Code, given inflow boundary values at points on the ballistics path. We computed pressure distributions on the projectile, assuming a smooth cannon surface. Integration of the distribution over the projected lateral surface of the projectile gives an estimated side force of 500,000 pounds on the projectile as it enters the brake section of the tube. In a yawed attitude, such forces can effect inertial instabilities on the projectile which, in turn, contribute to balloting and mechanical wear of the tube. The same numerical solution computes local heat transfer rates on the obturator and rotating band surfaces. The effect of blow-by flow heat transfer on tube erosion is a factor that is not well understood. An extension of the present work will provide a basis for further understanding the combined effects of abrasive and chemical erosion. The present computations assume that the wear gap between projectile and cannon wall is 0.020 inch and that the obturator protrudes 70 into the gap. Results are presented at two points on the ballistics trajectory, 2.212 and 5.256 meters from the rifle origin. Local heat transfer to the barrel wall was obtained for projectiles with and without obturator and band. At the 2.212 meter location, the latter yielded maximum local heat transfer rates on the barrel surface that exceeded 30 times the heat transfer computed at 1.7 inches upstream of the projectiles base i.e., in the projectiles wake boundary layer. With the obturator and band, and at the same travel point, the heat transfer ratio peaked at 2040, with the wake heat transfer computed at 6.7 inches upstream of the projectiles base.