Experimental And Numerical Investigations On The Oil Sealing Characteristics Of The Labyrinth Seal

Labyrinth seal,being the most typical seal form of aero-engine,is widely used for sealing oil and air.Labyrinth seal has a significant effect on aero-engine performance such as efficiency,engine thrust and oil consumption rate.The air sealing characteristics were investigated extensively in the last several decades.However,there are few studies on the oil sealing characteristics of labyrinth seal in open literatures because sealing air is the initial function of labyrinth seal.To explore the influence of operating condition and geometric construction on oil sealing characteristics,the oil leakage of labyrinth seals in different geometric forms was measured under different operating conditions based on the labyrinth seal of the bearing cavity in an aero-engine.Then the flow field of gas in the labyrinth seal was obtained numerically to investigate the inner mechanism and provide reference to labyrinth seal design and application.The main contents are as follows:1.Based on the labyrinth seal geometric construction of the bearing cavity in an aero-engine,fourteen labyrinth seals were designed,which involved with different geometric construction such as tooth width,tooth distance,tooth quantity,tooth shape,sealing clearance and angle of oil-swinging tooth.The oil leakage of these labyrinth seals was measured under different operating conditions,such as rotating speed,pressure ratio and oil supply.The influence upon oil sealing characteristics was acquired and the reason was analyzed.Results show that,rotating speed has great influence on oil sealing characteristics.As rotating speed increases,a oil ring appears near the tooth tip under the effect of viscous force,which decreases the sealing clearance.Oil leakage decreases as the pressure ratio increases,but the variety range is different under various operating conditions and geometric constructions.Oil leakage increases as the oil supply increases,and the trend is alike for similar geometric constructions.There is an optimum tooth width for the best oil sealing characteristics.Oil leakage decreases as tooth distance decreases under low rotating speed while the trend is weak under high rotating speed.More teeth mean less oil leakage while the influence recedes.Oil leakage decreases as the tooth shape changes from inclined tooth,unsymmetrical tooth to symmetrical tooth while the trend is not obvious under high rotating speed.Oil leakage increases as the sealing clearance increases.Oil leakage decreases as the angle of oil-swinging tooth increases.2.The flow field of gas in fourteen labyrinth seals was obtained under different rotating speed and pressure ratio numerically.The CFD results were analyzed according to the comparison of axial flow velocity,turbulent kinetic energy and pressure distribution.Combining the experimental results with numerical analysis,the inner mechanism of oil sealing was acquired.It is found that,the radial growth,which is caused by rotating motion,has little influence on sealing clearance.Increasing rotating speed means stronger vortex,stronger turbulent kinetic energy and larger range of low pressure,which is disadvantageous to sealing oil.Increasing pressure ratio leads to higher axial flow velocity,stronger turbulent kinetic energy and larger range of low pressure.Meanwhile,the pressure loss near the tooth tip is more serious as the pressure ratio increases.The velocity loss near the tooth tip increases as the tooth width increases,while the axial velocity of jet flow decreases.On the other hand,the turbulent kinetic energy loss near the toot tip decreases,which is benefit to sealing oil.As a result,the opposite effects make the change of oil leakage not monotonous.Increasing tooth distance makes the jet flow path longer,which leads to lower axial flow velocity and stronger vortex.More teeth mean higher pressure loss near tooth tip and lower axial flow velocity,which weaken the advantage of more teeth.Compared with unsymmetrical and symmetrical tooth,inclined tooth benefits the form of vortex.However,the tooth cavity of symmetrical tooth is large enough for the development of vortex,so sometimes its oil leakage becomes more.Increasing sealing clearance leads to larger flow area and higher axial velocity of jet flow,which makes the vortex more intense under the effect of friction.As the angle of oil-swinging tooth increases,the path of flow becomes shorter in the last tooth cavity,which means less energy loss.But the vortex becomes stronger at the same time,which weakens the advantage of larger angle of oil-swinging tooth to some extent.