涡流管流动结构及能量分离性能LDV实验研究

Experimental investigation of flow structure and energy separation performance of Ranque-Hilsch vortex tube with LDV measurement

设计了直径为30 mm的可组装式透明涡流管以实现主流道可视化,并采用二维激光多普勒测速(LDV)技术得到子午面时均流场.研究了不同冷流比(0.1~0.9)、主流道长度(360、600、900和1 200 mm)、入口压力(0.01、0.02 MPa)下的轴向速度和径向速度分布,特别是折返流边界对能量分离性能的影响.LDV结果表明,时均轴向速度分布具有较好的轴对称性,不同压力下流动结构具有相似性,径向速度远小于轴向速度.增加冷流比会导致折返流边界径向膨胀,揭示了在过短管和过长管中两种能量分离恶化机制--过短管中折返流面过厚,过长管中轴向滞止点向冷端靠拢.该结果验证了以往所提出的优化准则,同时可以说明滞止点并不是涡流管中的一种基本流动结构.

Diameter of 30 mm assembling transparent vortex tubes are designed for visualization of the main runner and a 2D laser Doppler velocimetry (LDV) technique is adopted to investigate the time-averaged flow field on the meridian plane.Various operation conditions with different cold mass fractions (0.1-0.9),tube lengths (360,600,900 and 1 200 mm),and inlet pressures (0.01 and 0.02 MPa) are studied to obtain the distributions of the axial and radial velocities and reveal how the reverse flow boundary affects the energy separation performance,particularly.The LDV results show that the time-averaged axial velocity distribution presents good axial symmetry,and the flow structure presents similarity under different pressures.Radial velocity is far less than the axial velocity.Increasing cold mass fraction leads to the radial expansion of reverse flow boundary.Two deterioration mechanisms in the energy separation performance of an excessively short or long tube are revealed: the over thick reverse flow boundary in the short tube,and the movement of the stagnation point toward to the cold end in the long tube.The proposed tube optimization criteria are proved.Meanwhile,it also shows that stagnation point is not a basic flow structure inside vortex tube.