Abstract:

Ejector is a common fluid supercharging equipment, and its mixing efficiency is low. To solve this problem, a new type of swirling ejector was proposed, which adds three-dimensional disturbing elements to the ejector driving nozzle to enhance momentum exchange efficiency. As a research object, its performance in air condition was studied experimentally and numerically. Compared with the traditional ejector, it can significantly improve the performance of ejector equipment. Under the sup-sonic condition, the three-dimensional disturbing elements cannot affect the mass flow of driving fluid, and the experimental measurement of the critical pressure point (P_RC) is unchanged, so that the boosting performance is guaranteed. The entrainment ratio (E_R) of the critical region increased to 5%. The numerical calculation results are in good agreement with the experimental ones. The flow field analysis of the numerical calculation shows that the spoiler elements installed at the tail of the ejector driving nozzle is useful. On the one hand, it can make the fluid mixing boundary increase. The petal-shaped fold appears, and the increase of the number of teeth can make more area of fluid mixing increases. On the other hand, the thickness of mixing area increases to 39.28%, the disturbing elements can make the axial velocity of driving fluid change into circumferential and radial velocity, the peak value of circumferential velocity changes from 0 to 5.5—20m/s, and the radial velocity increases from 25m/s to 30—47m/s. Swirling flow and radial turbulence make the ejector into three-dimensional momentum exchange. Under the sub-sonic condition of the momentum-enhanced elements, the entrainment ratio decreases, but the critical pressure point decreases, so that the supercharging capacity loses.

Key words: ejector, entrainment ratio, swirling flow, computational fluid dynamics (CFD), momentum transfer, mixing

摘要：

基于增大混合区域，增强动量交换效率的优化思想，添加三维扰流元件的动量增强型喷射器能够提高设备性能。以此为研究对象，本文在空气介质下对其性能进行了实验和数值计算研究。相较传统喷射器，动量增强型喷射器能显著提高喷射器单体设备性能。在超音速情况下，驱动流量不受影响，实验测定动量增强元件在增压性能变化不大的情况下，提升临界区引射率E_R达5%，数值计算结果与模拟结果吻合。对数值计算所得流场分析发现：在喷射器驱动喷嘴尾部设置动量增强元件，一方面能够使流体混合边界出现花瓣形褶皱，增大流体混合面积，同时增厚混合区域达39.28%，整体拓展混合空间；另一方面，动量增强元件能够促使驱动流体轴向速度转化为周向、径向速度，诱发周向旋流，增强径向扰流，变喷射器传统二维动量交换为三维动量交换。动量增强元件亚声速情况下，引射性能进一步提升，但其临界压力点降低，增压能力损失。

关键词: 喷射器, 引射率, 旋流, 计算流体力学, 动量传递, 混合