Flow separation and side-load behavior of the Vulcain engine

Abstract

The Vulcain engine flow separation and side-load behavior observed and measured during thrust chamber tests is discudded in detail in this paper. It is shown by the test results and by comparison with numerical flow data that the parabolic Vulcain nozzle features a transition in separation behavior from free shock separation to restricted shock separation and vice versa during both engine start-up and shut-down. These highly transient phenomena are a major cause of side-loads. In addition, the side-load activities are measured during nozzle operation with pre free shock separation or pure restricted shock separation. By using results from numerical simulations, it is shown that a specific plume pattern, the cap-shock pattern, is responsible for the observed flow transition. Finally, a comparison of the flow behavior in the Vulcain nozzle during start-up and shut-down is compared with other published data for thrust-optimized or parabolic rocket nozzles with an internal shock emanating from the throat.