喷射混合器放大效应的计算流体力学模拟

Computational Fluid Dynamics Simulation on the Scale-up Effect in Ejectors

选用Realizable k-ε湍流模型,对有扩散角度和无扩散角度的两种喷射器进行了计算流体力学(CFD)模拟,以研究喷射器的放大效应。在射流和引射速度不变的前提下,将两种喷射器的尺寸在初始尺寸的基础上分别放大3,5,8和10倍进行模拟计算。结果表明:对于两种喷射器,尺寸的放大对速度场以及湍动能的分布均无显著影响,而喷射器内湍流耗散率与涡量均随着喷射器尺寸放大倍数的增加而减小,近似成反比例关系,达到完全混合所需的距离与放大倍数成正比,无量纲距离略有变化。因为湍流耗散率及涡量等是表征湍动程度的重要指标,因此这也说明喷射器放大后湍动程度显著降低,不利于混合,这与喷射器是否存在扩散角度无关。

Computational Fluid Dynamics （CFD） simulation was employed to investigate the scale-up effect in ejectors with the Realizable k-e turbulent model. Two kinds of ejector models, with and without diffuser angle, were established. Keeping the velocities of jet flow and suction flow, the geometric sizes of ejectors were enlarged to 3, 5, 8 and 10 times based on the original sizes and the simulations were carried out respectively. The results showed that the velocity and turbulent kinetic energy were not changed apparently after scaled up, while the turbulent dissipation rate reduced significantly as well as the vorticity magnitude. There was an approximate inverse proportional relationship between the turbulent dissipation rate and the geometric size. Moreover, the distance required for mixing completely was proportional to the scale-up factor and the dimensionless distance changed slightly. Since the turbulent dissipation rate and the vorticity were important parameters to describe the turbulent flow, it might imply that the turbulent extent would drop significantly after scaled up, which was unfavorable for the mixing behavior. It had no relationship with the angle of the diffuser.