【摘要】 采用大涡模拟方法和单方程亚格子模式对小尺度量进行模拟。研究了不同强度壁面射流激励对圆管内气相流动的影响,模拟结果给出了射流对瞬态拟序结构发展、时平均流向速度分布的影响。随着射流强度的增加,射流入口附近流体的回流现象增强。射流强度足够大时可以减小管壁处的切应力值,同时会减小壁面附近流动速度,这种速度分布会导致气体夹带颗粒的能力下降,从而在实际两相流动中容易造成壁面附近的气粒返混现象。更多还原

【Abstract】 Large eddy simulation is performed to study the gas flow with near wall jet excitation in a pipe.One equation sub-grid scale(SGS) model is used for modeling sub-grid turbulence.Transport equation of passive scalar is also solved in order to perform numerical visualization of flow field.Computation is performed on a uniform grid system of 1027×45 nodes in the axial direction and radial direction respectively.The time integration of governing equations has been done with a second-order Adams-Bashforth scheme.The 2nd order finite difference scheme is used in space directions.Numerical simulation is performed by using Chorin’s fractional step method.Buneman variance of cyclic odd-even reduction algorithm is adopted for solving pressure correction Poisson equation.Simulation results give detailed information of transient behaviors of coherent structures at different evolution periods of turbulent channel flow.The effect of velocity disturbance on the evolution of coherent structures is also investigated.It is found that vortex roll-up process is initiated by the Kelvin-Helmholtz instability.With the increase of jet intensity,the size of the vortex is enlarged.Besides,there is a recirculation zone in the upstream of the jet excitation,and the recirculating flow changes stronger as the intensity of jet excitation increasing.With the jet velocity increasing,the shear stress at the wall can be reduced,and it will reaches to nearly zero value when the velocity of jet exceeds the main flow velocity.So,the jet excitation can reduce the drag force between the gas flow and the wall of the pipe.On the other hand,the velocity of gas flow in the near wall region is also reduced.This will give rise to reducing the ability of solid particles moving upward carried by gas phase in the fluid catalytic cracking(FCC) process,then it will cause solid particles and oil back-mixing in the near wall region of a riser,which will cause over-cracking and decrease the reaction selectivity.更多还原