气粒两相平面湍射流拟序结构的大涡模拟

Investigation of the Coherent Structure in a Particle laden Turbulent Planar Jet Using LES

:采用 Eulerian/L agrangian方法 ,对空间发展的气粒两相平面湍射流的非定常流动过程进行了数值模拟。以Re数为 130 0 0的平面不可压缩湍射流流动为例 ,气相场采用大涡模拟 ( large- eddy simulaiton,L ES)技术 ,直接求解大尺度涡运动的 Navier- Stokes方程 ,小尺度涡采用标准 Smagorinsky亚格子模式模拟。为了示踪两相射流中气相的运动 ,同时求解了标志物的浓度输运方程。颗粒相的运动用 L agrangian方法直接求解。大涡模拟结果表明 ,在平面射流的过渡区及充分发展区存在丰富的拟序结构及其相互作用。对于稀疏两相射流 ,不同 Stokes数的颗粒运动规律和浓度分布取决于颗粒惯性和气相拟序结构的共同作用。对于 Stokes数小于 10的两相射流 ,颗粒相的瞬时浓度场分布与拟序结构密切相关 。

The unsteady spatially-developing process of a particle-laden turbulent planar jet at a moderate Reynolds number (Re=13 000), was numerically simulated by using an Eulerian/Lagrangian approach. The large eddy simulation (LES) was used to simulate the turbulence of the continuous phase, where the motions of the large scale structures were solved directly through the incompressible Navier-Stokes equations and the effects of the unresolved scales were modeled by the standard Smagorinsky sub-grid-scale model. In order to visualize the coherent structures of the jet, as in the experiments, the transport equation for a passive scalar was also introduced and solved. Particles were tracked by computing the acceleration and motion equations of the individual spherical particle within the computational domain in a Lagrangian way. Results show that a rich variety of coherent structures generated by the instability of the shear layer and their detailed developing process in the proximal region of the jet can be simulated by the LES technique. As a dilute particulate planar jet flow is investigated, the motions of particles of different Stokes number is mainly determined by two factors, the inertia of particles and the coherent structure of the jet. The instantaneous distributive pattern of particles whose Stokes number is less than the order of 10 is closely related to the interactions between the particles and vortex. It is suggested to take into account such effects when the particle dispersion in shear flows is studied.