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.
Numerical examination of two-dimensional smolder structure in polyurethane foam
Abstract Although smolder combustion has been extensively studied both computationally and experimentally, relatively few theoretical studies have examined the two-dimensional structure of the smolder wave. In this paper, two-dimensional smolder in polyurethane foam is modeled with a two-dimensional numerical formulation that includes a seven-step kinetic model of the polyurethane smolder reaction mechanism. The two-dimensional model formulation includes the effects of heat, mass, species, and momentum transfer of the porous solid and gas phase. The seven-step decomposition reaction mechanism, which includes a secondary char oxidation and an additional char pyrolysis step, was developed using genetic algorithm optimization. The mechanism is capable of modeling both forward and opposed smolder. The model was used to study the two-dimensionality of a forward propagating smolder wave. The model results show a two-dimensional structure in the temperature, species, and reaction profiles that agrees qualitatively with experimental observations. Oxygen is consumed at the reaction front, as expected, which leads to different reaction pathways governing the final products (i.e. thermal char and oxidative char). It was found that the model response is sensitive to boundary conditions, thermal properties, and heats of reaction for the char oxidation reaction. The incorporation of the secondary oxidation reaction step in the model paves the way to further analysis of the transition to flaming process.
Career Choice Inclination of the College Graduates——under the Analytic Framework on the Basis of LMS Theory
Employment difficulty of college graduates has become a social problem in China today.The research group has found that college graduates have a strong inclination in career choice considering units and regions.In terms of China's manpower market and the segmented labor market theory,it is found that their inclination is caused by the great income gap of different regions,the high cost of job transfer,and the sharp differences in social welfare.It is thus obvious that solution to the problem lies with the gradual breakdown of the institutional segment of labor market.