Large eddy simulations （LES） have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center （DLR）. Turbulent combustion is mod- eled by the tabulated thermo-chemis...Large eddy simulations （LES） have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center （DLR）. Turbulent combustion is mod- eled by the tabulated thermo-chemistry approach in combination with the presumed probability density function （PDF）. A/3-function is used to model the distribution of the mixture fraction, while two different PDFs, g-function （Model I） and //-function （Model II）, are applied to model the reaction progress. Temperature is obtained by solving filtered energy transport equation and the reaction rate of the progress variable is rescaled by pressure to consider the effects of compressibil- ity. The adaptive mesh refinement （AMR） technique is used to properly capture shock waves, boundary layers, shear layers and flame structures. Statistical results of temperature and velocity predicted by Model II show better accuracy than that predicted by Model I. The results of scatter points and mixture fraction-conditional variables indicate the significant differences between Model I and Model II. It is concluded that second moment information in the presumed PDF of the reaction progress is very important in the simulation of supersonic combustion. It is also found that an unstable flame with extinction and ignition develops in the shear layers of bluff body and a fuel- rich partially premixed flame stabilizes in the central recirculation bubble.展开更多
基金financial support by the National Natural Science Foundation of China (Nos. 51176178, 50936005)
文摘Large eddy simulations （LES） have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center （DLR）. Turbulent combustion is mod- eled by the tabulated thermo-chemistry approach in combination with the presumed probability density function （PDF）. A/3-function is used to model the distribution of the mixture fraction, while two different PDFs, g-function （Model I） and //-function （Model II）, are applied to model the reaction progress. Temperature is obtained by solving filtered energy transport equation and the reaction rate of the progress variable is rescaled by pressure to consider the effects of compressibil- ity. The adaptive mesh refinement （AMR） technique is used to properly capture shock waves, boundary layers, shear layers and flame structures. Statistical results of temperature and velocity predicted by Model II show better accuracy than that predicted by Model I. The results of scatter points and mixture fraction-conditional variables indicate the significant differences between Model I and Model II. It is concluded that second moment information in the presumed PDF of the reaction progress is very important in the simulation of supersonic combustion. It is also found that an unstable flame with extinction and ignition develops in the shear layers of bluff body and a fuel- rich partially premixed flame stabilizes in the central recirculation bubble.
文摘大规模MIMO系统中,相对于其他基于信道矩阵分解的波束成形算法,如迫零、最小均方误差算法等,匹配滤波(Matched filter,MF)具有复杂度极低的优点,从而成为一种极具实用潜力的波束成形算法。鉴于此,本文推导了基站采用MF波束成形算法时,用户端信干噪比(Signal-to-interferenceand-noise ratio,SINR)的近似概率密度函数(Probability density function,PDF)。该函数对于推导与分析系统性能,如和速率、中断概率等至关重要。仿真表明:当基站天线数趋于大规模时,SINR公式的PDF曲线趋近于通过纯仿真得到的PDF曲线。
