Experimental Investigation On Flowing Characteristics Of Labyrinth Seals In Aeroengine

Experimental investigation of stepped and straight-through labyrinth seals was designed to study the sealing performance of two different typical labyrinth seals widely used in aeroengines. The effects of pressure ratio, labyrinth sealing gap, cavity depth and cavity width, tooth number and bush structure on the flowing characteristics were studied. The pressure disruption and contribution to the total pressure drop of each tooth cavity along the flow direction was measured. In order to facilitate dimensional analysis on the flow resistance characteristics of labyrinth seals, the variable cross-section of the flow channels are considered as constant cross-section flow. The mechanical energy loss of flow caused by throttle turbulence intensity is considered as caused by friction along the way. The expression of friction coefficient f=F(Re, Dh/L) and fRe=F(Ma, Dh/L) were obtained from a lot of experimental data. The calculated leakage rates of constant cross-section channel and labyrinth seal was compared and the leakage rate of labyrinth seal is less at the same pressure ratio.According to the literature survey and research purposes of this article,20straight-through labyrinth seal test pieces,28stepped-through labyrinth seal and8bushes with different structures were designed. The pressure ratio is in the range of1.1to3.5, and the sealing gap is in the range of0.2～0.6mm.The common flow characteristics of stepped and straight-through labyrinth seals were summarized as follows:The leakage loss increases as the cavity depth increases and it decreases as the cavity width increases in certain conditions. The thickness of tooth tip has little effect on the sealing performance. The leakage rate decreases rapidly as the cavity number increases. The leakage rate decreases by about45%as the tooth number increases from2to5for straight-through labyrinth seals. And it decreases by about28%as the tooth number increases from3to5for stepped labyrinth seals. The contribution to the total pressure drop of each tooth cavity gradually becomes less along the flow direction. The leakage rate of stepped labyrinth seal is less than that of straight-through labyrinth seal by more than40%for the stepped labyrinth seal eliminates kinetic carryover effect.The groove on the bush has an adverse effect on its sealing performance. The groove can lead to the leakage rare increasing by about30%. Step bushes of1.5mm,2.5mm and3.5mm height were designed. The sealing performance improves as the step bushes height improves. The effects of relative axial location on the leakage were investigated. The leakage is max when the tips of the teeth are at the center position of brushes.