Study On Derivation Characteristics Of Channel Wakes With Hemisphere At The Bottom

There are many opportunities to observe turbulent flows in our everyday surroundings or engineering problems.It is the key problem with both great theoretical meanings and engineering applications in fluid mechanics.Channel turbulent flow is the most typical form of all the turbulent flows.In this paper,the channel flow with a hemisphere at the bottom is studied both numerically and experimentally by LES method and PIV experiment.Here are some main results:In terms of numerical simulation,numerical simulation of the channel flow with a hemisphere at its bottom is studied by LES method based on OpenFoam,an open source software.The effect of different Reynolds numbers on statistical characteristics and structure features,and the effect of hemihemisphere at the bottom on the anisotropy of the flow are investigated by changing initial conditions.It shows an obvious increase of turbulent kinetic and dissipation rate near the wall with the increase of Reynolds number.Besides,complex vortex structures are observed behind the hemisphere.Meanwhile,great anisotropy is presented in the spanwise direction,the area of which converges with that of rich vortex structures.The Reynolds stress owns a relatively strong anisotropy.From the aspect of the experiment,the channel flow with a hemisphere at its bottom is experimented by the PIV system.The results show that under the same inlet condition,turbulent statistic values of both asymmetric and symmetric channels will increase.Meanwhile,more complex vortex structures appear behind the hemisphere compared with the channel without hemisphere due to the hemisphere.Mean velocity,fluctuating velocity and Reynold stress of the experiment are analyzed and compared with that of numerical simulation.The experiment results correspond to the numerical results.In this paper,the Hilbert-Huang transform is used to analyze the three points of the numerical solution.The EMD mode is used to decompose the flow velocity time series of three points,and the intermittent and probability density functions of the internal model functions IMF after decomposition are studied.On this basis,the coherent structure of each mode and its reconstructed coherent structure are further studied.In addition,the results of the Fourier spectrum and Hilbert spectrum analysis are compared.