| Labyrinth seal is a kind of simple and reliable sealing structure. Typically it consists of a rotor, with multiple teeth on its circular surface, and a co-axial static bush. When flow pass through the passage between the rotor and the static bush, kinetic energy is quickly dissipated into heat, leakage flow was restricted. Engine efficiency is strongly dependent on the sealing effect of labyrinth seal. However, at present the detailed research on the leakage characteristics of some kinds of labyrinth seal, such as the structure with honeycomb bush and the transient condition with tooth cut into the static bush, is still in lack, the industry urgently needs the more completed database for labyrinth seal design. This thesis presents some deep study on these problems.Firstly, the author comprehensively reviewed the literature on the research of labyrinth seal, analyzed the effect of some major factors on the leakage characteristics. Then a rotating experiment rig for labyrinth seal leakage measurement was designed and established, which has a maximum rotating speed of 3000 rpm, maximum inlet pressure of 0.8 MPa, and allowed teeth tip diameter between 70~590 mm. By using this rig and numerical method, the leakage characteristics of three kinds of labyrinth seal were studied, which include straight-though labyrinth seal with smooth bush, straight-though labyrinth seal with honeycomb bush, and step labyrinth seal with smooth bush. The jet flow in the teeth cavity, the critical condition, and pressure loss in the flow passage of the seal have been studied. The effect of structure of the labyrinth seal, rotating speed and the pressure ratio of upstream and downstream of the seal on the leakage was investigated. Based on these studies, a new straight-through labyrinth seal was developed, which has a bush with a shallow groove machined opposite the teeth cavity. The experimental and numerical studies show that it has a better sealing effect.At start stage of the engine, the pressure in front of the seal gradually increase, the originally static fluid in the teeth cavity was driven into flow by the jet from the clearance between the tip of the teeth and the bush. Due to the viscous effect of the fluid, vortex was formed in the cavity, and the size and location of the vortex gradually change and finally reach a steady state. On the steady condition, the jet flow has the similar basic characteristics of two-dimensional wall jet flow. An empirical formula developed based on the 2D wall jet theory is better than that based on the free jet theory.The leakage coefficient of labyrinth seal rapidly increase with the increase of the upstream and downstream pressure ratio; but when the flow at the last tooth tip research chock condition, the leakage coefficient will no longer change with the further increase of the pressure ratio, while the critic section moves upward. For the studied clearance (< 0.25mm), the leakage coefficient of labyrinth-honeycomb bush structure is larger than labyrinth-smooth bush structure; upward step and downward step labyrinth seal have similar sealing performance, and both have a leakage coefficient 30% less than straight-through labyrinth seal. If not considering the variation of clearance caused by rotation and temperature change, rotating speed has negligible effect on leakage for all studied seals, except for, the leakage of step labyrinth seal linearly decrease with the increase of rotating speed at high rotating speed.The groove on the static bush, which is caused by the rub of tooth and bush, varies the wall jet flow condition. When the tooth cut in the groove, the leakage is reduced. The shallow groove manufactured on the smooth bush opposite to the tooth cavity destroys the continuity of the wall jet boundary layer, which lead to the jet flow change it direction and greatly improve sealing effect.
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