Overheating Anomalies during Flight Test Due to the Base Bleeding
In this paper we present the results of the analytical and numerical studies of the plume interaction with the base flow in the presence of base out-gassing. The physics-based analysis and CFD modeling of the base heating for single solid rocket motor performed in this research addressed the following questions: what are the key factors making base flow so different from that in the Shuttle [1]; why CFD analysis of this problem reveals small plume recirculation; what major factors influence base temperature; and why overheating was initiated at a given time in the flight. To answer these questions topological analysis of the base flow was performed and Korst theory was used to estimate relative contributions of radiation, plume recirculation, and chemically reactive out-gassing to the base heating. It was shown that base bleeding and small base volume are the key factors contributing to the overheating, while plume recirculation is effectively suppressed by asymmetric configuration of the flow formed earlier in the flight. These findings are further verified using CFD simulations that include multi-species gas environment both in the plume and in the base. Solid particles in the exhaust plume (Al2O3) and char particles in the base bleeding were also included into the simulations and their relative contributions into the base temperature rise were estimated. The results of simulations are in good agreement with the temperature and pressure in the base measured during the test.
Supersonic Base Flow Experiments in the Near Wake of a Cylindrical Afterbody
The near wake of a circular cylinder aligned with a uniform Mach 2.5 flow has been experimentally investigated in a wind tunnel designed solely for this purpose. Mean static pressure measurements were used to assess the radial dependence of the base pressure and the mean pressure field approaching separation. In addition, two-component laser Doppler velocimeter (LDV) measurements were obtained throughout the near wake including the large separated region downstream of the base. The primary objective of the research was to gain a better understanding of the complex fluid dynamic processes found in supersonic base flowfields including separation, shear layer development, reattachment along the axis of symmetry, and subsequent development of the wake
Turbulent base flow on an axisymmetric body with a single exhaust jet
Korst's two-stream theoretical base flow analysis is extended to treat base flow on an axisymmetric afterbody with a single operating exhaust nozzle. The flow around the afterbody and in the jet is supersonic with turbulent axisymmetric mixing occurring along the separated flow boundaries. The pressure in the base separated region ' increases in the downstream direction and is constant in a radial direction. A complete description of the base flow is obtained from the analysis permitting the prediction of base pressure and other flow parameters of interest. The analysis is shown to agree with experimental data. The results obtained from a parametric study performed with the analysis illustrate the influence on base drag of some of the significant geometric and operating parameters.