Effect of protrusion amount on gas ingestion of radial rim seal

In this paper, the effect of different amount of protrusion on various parameters in rotor–stator system was experimentally studied by measuring CO₂ concentration and pressure, in order to obtain the optimal protrusion amount. The parameters of different dimensionless sealing flow were measured under the condition that the annulus Reynolds number was 4.39 × 10⁵ and the rotating Reynolds number was 1.05 × 10⁶. The results show that the change of the amount of protrusions has little effect on the static pressure in the cavity, and the static pressure change near the sealing ring is almost negligible. But the total pressure and sealing efficiency increase first and then decrease with the increase of the amount of protrusion. The variation of power consumption is the same. A complex vortex structure will appear at the high radius region when the protrusion is installed. On the other hand, the protrusion can effectively reduce the minimum sealing flow of the rotor–stator cavity. Furthermore, considering the sealing efficiency and power consumption, the best range of the protrusion amount is about 36. The ratio near this range can optimally balance the alleviation of the gas ingestion and the reduction of the power consumption.     

齿间凸起对直通篦齿封严特性影响的数值研究

为提升篦齿的密封性能,对在齿间光滑衬套上增加矩形凸起的直通篦齿的流动特性进行了数值研究,分析了压比、凸起的尺寸和轴向位置对篦齿泄漏特性的影响。和光滑齿相比,凸起破坏了壁面射流附面层的连续性,改变了流体在齿腔中的流动方向,有效地提高了通道的密封性能,降低了通道的泄漏量。结果表明,当压比为2时,含有凸起结构的篦齿的泄漏系数较光滑齿降低了13%,当压比增加到4时,泄漏系数更是降低了18%;凸起的高度越大宽度越小,凸起对篦齿密封性能的提高就越明显;凸起和下级齿之间的轴向距离越短,凸起对流入下级齿的气体流动方向改变就越大,密封性能也就越好。     

Effect of rotor-mounted protrusion on sealing performance and flow structure in rotor-stator cavity

This paper presents an experimental investigation on the effect of protrusion radial position and height on the sealing performance and flow structure in the rotor-stator cavity. The rotor-mounted protrusions are assembled at three radial positions and are set to three heights. The cavity is equipped with three rim seals: a radial seal, an axial seal and a seal with double fins on the stator. The annulus Reynolds number is set at $4.39\times {10}^5$ and the rotational Reynolds number ranges from $7.51\times {10}^5$ to $1.20\times {10}^6$. Heat and mass transfer analogy is applied. Pressure and ${\mathrm{C}\mathrm{O}}_2$ concentration are measured. The experimental results show that in cavities with different rim seals, radial distributions of the sealing efficiency, pressure and swirl ratio are basically the same. The sealing performance is improved by protrusions compared with the cavity without protrusion and improves with the increase of protrusion radial position and height. The effect of protrusion increases with the increase of the rotational Reynolds number. The windage loss and the flow resistance introduced by protrusions are investigated. It is found that induced windage loss and flow resistance decrease with the increase of protrusion radial position but increase with the protrusion height.     

Effect of the protrusion shape on gas ingestion of two sealing structures

The windage loss caused by protrusion in a rotor–stator cavity has been studied in detail, and there are abundant fitting formulas that have been summarized to calculate the moment coefficients. Some other theorists have emphasized its effect on the sealing efficiency, proposing that installation of protrusion could alleviate gas ingestion. However, the protrusion shape which is an influential factor on the sealing efficiency has not been focused in previous research. Using the experimental method of measuring CO₂ volume fraction, cavity pressure, and power consumption, we investigated the effects of several typical protrusion shapes on various parameters for two sealing structures, in order to obtain the optimal shape. Results showed that a variation of the protrusion shape had little impact on the static pressure, but the total pressure and the sealing efficiency increased in different degrees. Furthermore, even though the hexagon shape resulted in the highest sealing efficiency, we observed that the drop shape had the best overall performance in all of the eight models, which could result in higher efficiency of the turbine cavity. The combination of a radial seal structure and protrusion could improve sealing efficiency better.