The Lattice Boltzmann method （LBM） is used to simulate the flow field in a bifurcate channel which is a simplified model of the draft tube of hydraulic turbine machine. According to the simulation results, some qual...The Lattice Boltzmann method （LBM） is used to simulate the flow field in a bifurcate channel which is a simplified model of the draft tube of hydraulic turbine machine. According to the simulation results, some qualitative conclusions can be deduced. The reason of uneven flux in different branches of draft tube is given. Not only the vortex rope itself, but also the attenuation of the rotation strength is important in bringing on the uneven flux. The later leads to adverse pressure gradient, and changes the velocity profile. If the outlet contains more than one exit, the one that contains the vortex rope will lose flux because of this adverse pressure gradient. Several possible methods can be used to minimize the adverse pressure gradient domain in order to improve the efficiency of turbine machine.展开更多
Homogeneous isotropic turbulence has been playing a key role in the research of turbulence theory.And the pseudo-spectral method is the most popular numerical method to simulate this type of flow fields in a periodic ...Homogeneous isotropic turbulence has been playing a key role in the research of turbulence theory.And the pseudo-spectral method is the most popular numerical method to simulate this type of flow fields in a periodic box,where fast Fourier transform(FFT)is mostly effective.However,the bottle-neck in this method is the memory of computer,which motivates us to construct a memory-saving algorithm for spectral method in present paper.Inevitably,more times of FFT are needed as compensation.In the most memory-saving situation,only 6 three-dimension arrays are employed in the code.The cost of computation is increased by a factor of 4,and that 38 FFTs are needed per time step instead of the previous 9 FFTs.A simulation of isotropic turbulence on 20483 grid can be implemented on a 256G distributed memory clusters through this method.展开更多
基金supported by the Key Project of National Natural Science Foundation of China (10532010)
文摘The Lattice Boltzmann method （LBM） is used to simulate the flow field in a bifurcate channel which is a simplified model of the draft tube of hydraulic turbine machine. According to the simulation results, some qualitative conclusions can be deduced. The reason of uneven flux in different branches of draft tube is given. Not only the vortex rope itself, but also the attenuation of the rotation strength is important in bringing on the uneven flux. The later leads to adverse pressure gradient, and changes the velocity profile. If the outlet contains more than one exit, the one that contains the vortex rope will lose flux because of this adverse pressure gradient. Several possible methods can be used to minimize the adverse pressure gradient domain in order to improve the efficiency of turbine machine.
基金support from National Natural Science Funds for Distinguished Young Scholar group under Grant No.10921202National Climb Plan under Grant No.2009CB724100.
文摘Homogeneous isotropic turbulence has been playing a key role in the research of turbulence theory.And the pseudo-spectral method is the most popular numerical method to simulate this type of flow fields in a periodic box,where fast Fourier transform(FFT)is mostly effective.However,the bottle-neck in this method is the memory of computer,which motivates us to construct a memory-saving algorithm for spectral method in present paper.Inevitably,more times of FFT are needed as compensation.In the most memory-saving situation,only 6 three-dimension arrays are employed in the code.The cost of computation is increased by a factor of 4,and that 38 FFTs are needed per time step instead of the previous 9 FFTs.A simulation of isotropic turbulence on 20483 grid can be implemented on a 256G distributed memory clusters through this method.
