Investigation On Leakage And Lifting-force Characteristics Of Finger Seal With Lifting-pads

Finger seal is new developed sealing technology after labyrinth seal and brush seal, which can beused in compressor and turbine in order to decrease leakage. Flow resistance is increased because ofmultiple staggered layers of finger seal, therefore the leakage is reduced.Basic finger seal is proposed firstly, but there is friction heat between it and rotor because of theirinterference fit, so increase in local temperature of the flow shorten the seals’ durability and life. Sothe airflow’ stream and heat transfer characteristics of the finger seal are studied.Some foreign scholars have started to study finger seal with lifting-pads since the late1990s. The“finger seal with lifting-pads” was proposed by Arora. It is different from basic finger seal because ithas lifting-pads in its lower pressure fingertips boots, and it can reduces abrasion because of fluidspace formed between seals and rotor. So, it solves the problem of basic finger seal. Therefore, theleakage characteristics of finger seal with lifting-pads are studied.The study of this paper is as follows:Firstly, the author reviewed lots of literatures about the finger seal, and analyzed the effect ofsome major factors on the leakage characteristics and heat transfer characteristics.Secondly, the author studied the airflow’ stream and heat transfer characteristics of the basicfinger seal using porous model. The study indicates: the temperature of contact position (rear of thefingertips boots) between seal and rotor is highest, and the maximum temperature increases with theincrease of interference and rotating speeds, while decreases because of the increases of pressuredifferentials.Lastly, the author designed the finger seal with lifting-pads, and studied its leakage andlifting-force characteristics using three-dimensional model in this essay. The author studied the effectof pressure differentials and other factors on leakage, as well as the distribution of streamline andpressure under surface of lifting-pads are also obtained. The research work is as follows: when sealgap and pressure differentials increase, the total leakage increases; with the increase of pressuredifferentials the flow factor increases, but its increment gradually declines; the rotor speeds almost hasno effect on total leakage and flow factor; increasing layers of high pressure seals has influence ontotal leakage; leakage characteristics of this structure is better than basic finger seals; the asymmetryof pressure distribution under surface of the lifting-pads is caused radically by rotation of the rotor;the pressure value under surface of lifting-pads changes obviously because of pressure differentials, while the pressure differentials hardly has influence on the asymmetry of pressure distribution; thelifting-force increases with the decrease of seal gap, but the asymmetry becomes more and moreobvious; the lifting-force factor increases with the increase of pressure differentials; the lifting-forcefactor decreases with the increase of seal gap; while the rotor speeds increases, the lifting-force factordecreases.