Optical Measurements of Muzzle Blast

The structure of the flowfields formed about the muzzle of a small caliber rifle during the firing are measured using a time-resolved, spark shadow-graph technique. The initial flow from the muzzle occurs as tube gases are forced out ahead of the projectile. The gas is air and the exit properties are Ve =945 m/sec, Me = 1.48 and Pel POO = 15. A second flowfield forms upon separation of the projectile which releases the propellant gases. After an initial, in-bore expansion, the propellant gas muzzle properties are Ve=\29S m/sec, Afe = 1.0, and Pe/Poo =600. While the exit properties are different, the flowfields develop in a similar manner. In the axial or downrange direction, strong coupling between the jet and blast fields is observed; however, along the lateral boundaries, the coupling is very weak with the jet structure remaining invariant once established. Motion of observable discontinuities along the axis of symmetry is shown to qualitatively agree with variable energy blast wave theory. At late times, the air blast and jet flows are shown to uncouple and decay independently.