In this paper, we establish a differential equation about scalar curvature of conformally flat K-contact manifolds, and prove that a conformally symmetric K-contact manifold is a Riemann manifold with constant curvatu...In this paper, we establish a differential equation about scalar curvature of conformally flat K-contact manifolds, and prove that a conformally symmetric K-contact manifold is a Riemann manifold with constant curvature 1. At the same time, the results on Sasaki manifolds which are given by Miyazaawa and Yamagushi are generalized to K-contact manifolds.展开更多
Systematic experimental work was conducted to investigate the solid acceleration length in a 16m long circulating fluidized bed riser with fluid cracking catalyst particles over a wide range of operating conditions. A...Systematic experimental work was conducted to investigate the solid acceleration length in a 16m long circulating fluidized bed riser with fluid cracking catalyst particles over a wide range of operating conditions. A more feasible method is proposed to determine the acceleration length from the measured axial profiles of pressure gradient (or apparent solid holdup). With this new method and large amount of experimental data, a clear picture on the variation of the acceleration length with both solid circulating rate and superficial gas velocity is obtained.It is found that the acceleration length increases generally with increasing solid flow rate and/or decreasing gas velocity. However, the trend in variation of the acceleration length with operating conditions are quite different in different operation ranges. Reasonable explanations are suggested for the observed variation patterns of acceleration length.展开更多
This paper investigates the main scale analysis of the aerodynamic noise in the foremost bogie area by the large-eddy simulation(LES)and the Ffowcs Williams-Hawkings(FW-H)analogy.The mechanism of the aerodynamic noise...This paper investigates the main scale analysis of the aerodynamic noise in the foremost bogie area by the large-eddy simulation(LES)and the Ffowcs Williams-Hawkings(FW-H)analogy.The mechanism of the aerodynamic noise in this area has been excavated.The aerodynamic excitation results show that the bogie divides the bogie compartment into two cavities,each of which contains a large circulating flow and presents multi-peak characteristics in the frequency domain.The far-field noise results suggest that in the speed range of 200−350 km/h,the aerodynamic noise mechanism in the bogie area is the same.Cavity noise is the main noise mechanism in the foremost bogie area,and the bogie divides the bogie cabin into two cavities,thereby changing the aerodynamic noise in this area.展开更多
The structural characteristics of 2004 typhoon Aere's precipitation are analyzed using the high-resolution data from the Tropical Rainfall Measuring Mission(TRMM) of the National Aeronautics Space Administration(N...The structural characteristics of 2004 typhoon Aere's precipitation are analyzed using the high-resolution data from the Tropical Rainfall Measuring Mission(TRMM) of the National Aeronautics Space Administration(NASA).It is found that the typhoon's characteristics vary at different stages of its development.To analyze the asymmetric causation of precipitation distribution,data from the National Center for Environmental Prediction(NCEP) reanalysis are used to calculate the vertical integral of the water vapor flux vector.The results show that because of this process,along with the unique phenomenon of twin-typhoon circulation,the easterly air current of the typhoon's northern side and the southwesterly air current of its southern side play a joint role in transporting water vapor.Furthermore,its transport effects vary greatly at the different stages of development,showing the peculiarity of the water source for this typhoon process.The distributions of the typhoon convection area—characterized by heavy precipitation and a maximum-value area of the water vapor flux,as well as a strong ascending-motion area—differ at different stages of the typhoon's development.The non-uniform distribution of water vapor flux and the vertical motion bring about asymmetrical distribution of the typhoon precipitation.展开更多
Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(...Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(Huang P G,Coleman G N,Bradshaw P.Compressible turbulent channel flows:DNS results and modeling.J Fluid Mech,1995,305:185-218).Using a concept of velocity-vorticity correlation structure(VVCS),defined by high correlation regions in a field of two-point cross-correlation coefficient between a velocity and a vorticity component,we have discovered a limiting VVCS as the closest streamwise vortex structure to the wall,which provides a concrete Morkovin scaling summarizing all compressibility effects.Specifically,when the height and mean velocity of the limiting VVCS are used as the units for the length scale and the velocity,all geometrical measures in the spanwise and normal directions,as well as the mean velocity and fluctuation(r.m.s) profiles become M-independent.The results are validated by direct numerical simulations(DNS) of compressible channel flows with M up to 3.Furthermore,a quantitative model is found for the M-scaling in terms of the wall density,which is also validated by the DNS data.These findings yield a geometrical interpretation of the semi-local transformation(Huang et al.,1995),and a conclusion that the location and the thermodynamic properties associated with the limiting VVCS determine the M-effects on supersonic wall-bounded flows.展开更多
The flow structure around the intake of a vertical pump is investigated experimentally and numerically in order to obtain a guideline in designing the optimum shape of the intake of vertical pumps, in which their inst...The flow structure around the intake of a vertical pump is investigated experimentally and numerically in order to obtain a guideline in designing the optimum shape of the intake of vertical pumps, in which their installation area is demanded to be minimum without losing the high performance. We concentrate our attention on the expansion ratio of the intake as a representative characteristic of the shape of the pumps and investigate the effect of the expansion ratio on pump performance. It is concluded that the optimum expansion ratio ranges in 1.1-1.2 if we take into consideration that the area needed for the installation of the pump should be minimum.展开更多
Rotor blades in a radial turbine with nozzle guide vanes typically experience harmonic aerodynamic excitations due to the rotor stator interaction. Dynamic stresses induced by the harmonic excitations can result in hi...Rotor blades in a radial turbine with nozzle guide vanes typically experience harmonic aerodynamic excitations due to the rotor stator interaction. Dynamic stresses induced by the harmonic excitations can result in high cycle fatigue(HCF) of the blades. A reliable prediction method for forced response issue is essential to avoid the HCF problem. In this work, the forced response mechanisms were investigated based on a fluid structure interaction(FSI) method. Aerodynamic excitations were obtained by three-dimensional unsteady computational fluid dynamics(CFD) simulation with phase shifted periodic boundary conditions. The first two harmonic pressures were determined as the primary components of the excitation and applied to finite element(FE) model to conduct the computational structural dynamics(CSD) simulation. The computed results from the harmonic forced response analysis show good agreement with the predictions of Singh's advanced frequency evaluation(SAFE) diagram. Moreover, the mode superposition method used in FE simulation offers an efficient way to provide quantitative assessments of mode response levels and resonant strength.展开更多
文摘In this paper, we establish a differential equation about scalar curvature of conformally flat K-contact manifolds, and prove that a conformally symmetric K-contact manifold is a Riemann manifold with constant curvature 1. At the same time, the results on Sasaki manifolds which are given by Miyazaawa and Yamagushi are generalized to K-contact manifolds.
基金the National Natural Science foundation of China (No. 29928005).
文摘Systematic experimental work was conducted to investigate the solid acceleration length in a 16m long circulating fluidized bed riser with fluid cracking catalyst particles over a wide range of operating conditions. A more feasible method is proposed to determine the acceleration length from the measured axial profiles of pressure gradient (or apparent solid holdup). With this new method and large amount of experimental data, a clear picture on the variation of the acceleration length with both solid circulating rate and superficial gas velocity is obtained.It is found that the acceleration length increases generally with increasing solid flow rate and/or decreasing gas velocity. However, the trend in variation of the acceleration length with operating conditions are quite different in different operation ranges. Reasonable explanations are suggested for the observed variation patterns of acceleration length.
基金Project(2017YFB1201103)supported by the National Key Research and Development Plan of ChinaProject(2019zzts540)supported by the Graduate Student Independent Innovation Project of Central South University,China。
文摘This paper investigates the main scale analysis of the aerodynamic noise in the foremost bogie area by the large-eddy simulation(LES)and the Ffowcs Williams-Hawkings(FW-H)analogy.The mechanism of the aerodynamic noise in this area has been excavated.The aerodynamic excitation results show that the bogie divides the bogie compartment into two cavities,each of which contains a large circulating flow and presents multi-peak characteristics in the frequency domain.The far-field noise results suggest that in the speed range of 200−350 km/h,the aerodynamic noise mechanism in the bogie area is the same.Cavity noise is the main noise mechanism in the foremost bogie area,and the bogie divides the bogie cabin into two cavities,thereby changing the aerodynamic noise in this area.
基金A key project of National Foundation of Natural Science (40533015)Foundation for Meteorological Research of Jiangsu Province (K200715)a project of Foundation for Fundamental Theoretic Research of Institute of Meteorology,PLA University of Science and Technology
文摘The structural characteristics of 2004 typhoon Aere's precipitation are analyzed using the high-resolution data from the Tropical Rainfall Measuring Mission(TRMM) of the National Aeronautics Space Administration(NASA).It is found that the typhoon's characteristics vary at different stages of its development.To analyze the asymmetric causation of precipitation distribution,data from the National Center for Environmental Prediction(NCEP) reanalysis are used to calculate the vertical integral of the water vapor flux vector.The results show that because of this process,along with the unique phenomenon of twin-typhoon circulation,the easterly air current of the typhoon's northern side and the southwesterly air current of its southern side play a joint role in transporting water vapor.Furthermore,its transport effects vary greatly at the different stages of development,showing the peculiarity of the water source for this typhoon process.The distributions of the typhoon convection area—characterized by heavy precipitation and a maximum-value area of the water vapor flux,as well as a strong ascending-motion area—differ at different stages of the typhoon's development.The non-uniform distribution of water vapor flux and the vertical motion bring about asymmetrical distribution of the typhoon precipitation.
基金supported by the National Nature Science Foundation of China (Grant Nos.90716008,10572004 and 11172006)the National Basic Research Program of China (Grant No.2009CB724100)
文摘Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(Huang P G,Coleman G N,Bradshaw P.Compressible turbulent channel flows:DNS results and modeling.J Fluid Mech,1995,305:185-218).Using a concept of velocity-vorticity correlation structure(VVCS),defined by high correlation regions in a field of two-point cross-correlation coefficient between a velocity and a vorticity component,we have discovered a limiting VVCS as the closest streamwise vortex structure to the wall,which provides a concrete Morkovin scaling summarizing all compressibility effects.Specifically,when the height and mean velocity of the limiting VVCS are used as the units for the length scale and the velocity,all geometrical measures in the spanwise and normal directions,as well as the mean velocity and fluctuation(r.m.s) profiles become M-independent.The results are validated by direct numerical simulations(DNS) of compressible channel flows with M up to 3.Furthermore,a quantitative model is found for the M-scaling in terms of the wall density,which is also validated by the DNS data.These findings yield a geometrical interpretation of the semi-local transformation(Huang et al.,1995),and a conclusion that the location and the thermodynamic properties associated with the limiting VVCS determine the M-effects on supersonic wall-bounded flows.
文摘The flow structure around the intake of a vertical pump is investigated experimentally and numerically in order to obtain a guideline in designing the optimum shape of the intake of vertical pumps, in which their installation area is demanded to be minimum without losing the high performance. We concentrate our attention on the expansion ratio of the intake as a representative characteristic of the shape of the pumps and investigate the effect of the expansion ratio on pump performance. It is concluded that the optimum expansion ratio ranges in 1.1-1.2 if we take into consideration that the area needed for the installation of the pump should be minimum.
基金supported by the National Natural Science Foundation of China(Grant No.51276018)
文摘Rotor blades in a radial turbine with nozzle guide vanes typically experience harmonic aerodynamic excitations due to the rotor stator interaction. Dynamic stresses induced by the harmonic excitations can result in high cycle fatigue(HCF) of the blades. A reliable prediction method for forced response issue is essential to avoid the HCF problem. In this work, the forced response mechanisms were investigated based on a fluid structure interaction(FSI) method. Aerodynamic excitations were obtained by three-dimensional unsteady computational fluid dynamics(CFD) simulation with phase shifted periodic boundary conditions. The first two harmonic pressures were determined as the primary components of the excitation and applied to finite element(FE) model to conduct the computational structural dynamics(CSD) simulation. The computed results from the harmonic forced response analysis show good agreement with the predictions of Singh's advanced frequency evaluation(SAFE) diagram. Moreover, the mode superposition method used in FE simulation offers an efficient way to provide quantitative assessments of mode response levels and resonant strength.
