Studies of the two-phase plume jet and wall erosion in a vertical launching system.

摘要

The vertical launching system (VLS) produces a two-phase exhaust plume due to the metalized solid propellant employed in rocket motors. The gas management of the exhaust plume in the present VLS mainly comprises key issues: plume jet inducing the erosion of ablative materials used as thermal protection plates in the VLS, strong pressure waves travelling in the system, undesirable high rate of pressurization in the plenum chamber and central uptake duct in the VLS.;A series of subscale VLS tests were conducted to simulate the plume exhaust processes in the actual VLS. The experimental test rig was designed not only to closely simulate geometry of the actual VLS but also to match the dynamic behavior of the actual conditions. In addition, the diversified physical parametric conditions, including multiple-hole nozzle configuration, location, afterburn, and ablative sample repeatedly used, are tested to explore these influences on the dynamic responses of pressure waves and erosion. The influences of nozzle configuration, location of the active canister, and initial gas composition (afterburn) on the transient pressure-time traces are not as significant as their effects on the erosion pattern of the ablative sample.;In the theoretical study, a comprehensive model has been developed to describe the process of the plume impinging upon the ablative sample to produce the surface erosion. The behavior of exhaust plume is simulated by a turbulent circular jet impinging upon the sample under different aspect ratios and inlet turbulence conditions. The jet-impingement flow predicted by the theoretical model agreed with the experiment data in nonreacting impinging jets. The wall stress and pressure gradient, obtained by the two-layer turbulence model with the body-fitted coordinates in this study, showed a better prediction than other turbulence models in comparison with the experiment results. This analysis suggested that a higher jet height can reduce the wall stress, the Nusselt number and the stagnation-point pressure, which is the maximum pressure in the plenum. The erosion pattern predicted by the theoretical model is slightly underpredicted in compared with the measured erosion contour of test firing. This slight underprediction is probably caused either by mechanical erosion associated with aluminum-oxides particles striking on the sample or by the uncertainties in chemical kinetic rates in the material.