Abstract: The design of inlet size for hydrocyclone is an effective method to improve separation accuracy. However, for a long term, the study on hydrocylone inlet size is largely dependent on practical experience. Few studies have been on the influence of inlet size on the hydrocyclone flow field. In this article, the flow field inside a 50 mm hydrocyclone is investigated with CFD method. The pressure profile, three-component velocity distribution and secondary vortex structure are analyzed. The results show that the tangential velocity is the component being affected most since it grows apparently, while the axial and radial velocities vary less, which means that the centrifugal factor increases while the separation structure keeps similar. The swirl velocity of the flow in the far side from the inlet is reinforced. The double-peak phenomenon is found in axial velocity and the reduction of inlet size magnifies this effect. In this sense, the flow field with smaller inlet is prone to better separation. However, smaller inlet size facilitates the formation of secondary vortexes and enhances the entrainment of fluid by the injected flow, which may hamper the separation. Thus, the cut-off size will not always decrease with the reduction of inlet size. Moreover, the increase of energy consumption is mostly attributed to the greater local loss in the connection of inlet and cylinder and the formation of more secondary vortexes.

Key words: inlet size, CFD, hydrocyclone flow structure, turbulent flow, separation

摘要： 力旋流器进口尺寸的设计是提高分离精度的一种有效方法。长期以来，对旋流器进口尺寸影响分离性能的认识主要来自工程实践经验，鲜见从旋转流场和分离机理的角度进行系统性分析的报道。采用计算流体力学方法进行旋转流场模拟，并考察进口尺寸缩小后的压力分布特性、三向速度分布和二次涡流结构。研究结果表明：进口尺寸缩小后切向速度数值的上升趋势明显，同时轴向速度和径向速度数值上相对变化较小，管内离心强度显著增高的同时保留了主要的分离结构。而且柱段流体，尤其是远离进口一侧的流体旋转更为充分，轴向速度双峰结构也更为明显。从上述角度来看，进口尺寸缩小后的流场分布情况更加有利于分离。但是，进口尺寸的缩小会加剧旋流管内的二次涡流运动，增大进口处射流的卷吸作用，使流场更加不稳定，从而对分离产生不利影响，因此分离粒度不可能随着进口尺寸的缩小无限制地降低。另外，进口尺寸缩小后，局部损失增大，且二次涡流运动加剧，导致旋流管的能耗会有一定的增加。

关键词: 进口尺寸, 计算流体力学, 旋转流场结构, 湍流, 分离