Nonuniform Clearance Effects on Windage Heating and Swirl Development in Straight-Through Labyrinth Seals

Straight-through labyrinth seals are reliable noncontact seal structures widely used in aeroengines. Windage heating and swirl development of labyrinth seals are of great significance to the design of secondary air systems. In the operation process of an aeroengine, a labyrinth seal is supposed to experience uneven temperature distribution, which may cause deformation and resulting nonuniformity along the flow direction. The nonuniformity coefficient was defined to characterize the degree of nonuniformity so that the influence of nonuniform clearance on windage heating and swirl development can be analyzed quantitatively. Windage heating and swirl development were analyzed from the perspectives of different Reynolds numbers, pressure ratios, circumferential Mach numbers, and dimensionless minimum tip clearances. Simulation results showed that when other dimensionless parameters are the same, both windage heating number and exit swirl ratio decrease with the increase of the nonuniformity degree. With the same nonuniform degree, the decrease rate of divergent clearance is larger than that of convergent clearance. The changing trends of the decrease rate of both windage heating number and exit swirl ratio were analyzed in detail. It can be concluded that the decrease rate of the exit swirl ratio reaches the peak when the dimensionless minimum tip clearance is about 0.067. This result makes it clear that the effect of nonuniform clearance is indispensable for the safety assessment of aeroengines.