Study On Leakage Characteristics Of Gas Lubricated Deep-Hole-Pattern Annular Seals

Based on favorable leakage characteristics and rotordynamic characteristics,deep-pores annular seals have been widely used in turbine machinery,such as steam turbines,gas turbines,compressors and aeroengines.However,the mechanism of deep-pores annular seals is not clear.In this paper,based on vortex effect caused by deep pores,leakage characteristic of deep-pores annular seals was analyzed to promote the design theory for seals with deep pores.Firstly,based on flow coefficient modified Reynolds equation,the mathematical model used to analyze leakage characteristic of gas lubricated annular seals was established.Influence of vortex effect on flow rate for both pressure flow and shear flow of a two dimension rectangle groove unit was calculated by using CFD model.Numerical results show that vortex effect becomes significant and the accuracy of Reynolds equation declines with increasing groove depth.Secondly,the validity of vortex model for gas lubricated deep-pores surface was verified by relative theory and experimental data.For theoretical proving,flow rate of a three dimensional unit with a deep hole was carried out by using vortex model and CFD model.As to experimental verification,flow rate of a honeycomb seal calculated by vortex model was compared with that of Child's experimental data.Results of vortex model agree well with both CFD model and experimental data.Thirdly,the influence of hole type and hole arrangement on flow characteristics was analyzed by using vortex model.Results show that flow rate of paralleled-hole clearance is less than that of the staggered-hole surface with the same hole type;with the same arrangement,square hole seals have the minimum flow rate and the hole-pattern seals have almost same results to that of honeycomb seals.Finally,based on vortex model,how the geometric parameters,distribution parameters and operating parameters affect the leakage of annular seals was carried out.It is found that leakage decreases as hole depth,seal length and hole number increase and clearance decrease.Higher inlet pressure causes the larger leakage.Rotor speed has little effect on the leakage.For the present paper,the analysis of leakage characteristic of gas lubricated annular seals can enrich and perfect the theoretical analysis models,give a conduction to the engineering application and possess certain theoretical and engineering value.