Two-phase plume impingement effects

Abstract

Tests were conducted in a blow-down type, two-phase, supersonic wind tunnel using helium carrier gas to accelerate micron-sized aluminum oxide particles to velocities ranging from 1300 to 2300 m/sec. The particle mass flux ranged from 0.4 to 2.6 g/cm sec which corresponds to conditions typical of the near field of solid-propellant motors. A number of target materials were tested including stainless steel, teflon, carbon cloth phenolic, quartz cloth phenolic, ATJ graphite, and pyrolytic boron nitride. In order to determine the effect of angle of incidence on the nature of the particlesurface interaction, the targets were designed to provide information on impingement forces over the full range from grazing to normal impact. Specifically, impact angles of 90° (normal), 60°, and 20° were selected. Force measurements were made with a three component balance. The balance was instrumented to detect directly the axial force and two bending moments, where the latter could be resolved into the transverse component of force and a pure residual moment acting on the target. In addition, the flowfield surrounding the target was examined photographically, using schlieren and light transmission and scattering techniques. For the range of experimental conditions, the particle impact was found to be inelastic for moderate to large angles of incidence and partially elastic for grazing incidence. The measured forces, which were observed to be independent of particle size, shock layer gas density and target material, were less than the theoretical forces by an amount dependent only on the angle of incidence. The most significant experimental result, however, was the discovery that a dense debris layer, comprised primarily of spent projectile material, formed immediately ahead of the target, partially shielding it from subsequent impact by oncoming particles. Although a large fraction of the incident particle momentum diffused through the layer and was transferred to the target, a significant fraction of the incident particle kinetic energy was absorbed by the impact debris with a corresponding decrease in target damage. The latter effect was accentuated with increasing particle mass flux where relative target damage, i.e., the ratio of target mass loss to mass of impinging particles, was observed to rapidly diminish.