Effects of Reynolds number and pressure ratio on leakage loss and heat transfer in a stepped labyrinth seal

The influence of Reynolds number and pressure ratio on the operating charac teristics of a stepped labyrinth seal was experimentally determined. The ge ometries investigated represent designs of a stepped labyrinth seat typical for modern jet engines. Heat transfer and discharge measurements were obta ined for two plane models with various seal clearances. The experiments cov ered a range of Reynolds numbers and pressure ratios. Independent variation of Reynolds number and pressure ratio was obtained by adjusting the back p ressure at the seal exit for a given pressure ratio. Dimensionless discharg e coefficients, describing the sealing performance, were derived from the m easured leakage rates. Pressure ratio, Reynolds number tip geometry, and se al clearance all affected the sealing performance. Finite element calculati ons were employed to calculate the local heat transfer coefficients from th e measured wall and gas temperatures. Averaging of the local values yielded mean heat transfer coefficients and mean Nusselt numbers. The heat transfe r was mainly determined by the Reynolds number Compressibility effects on t he heat transfer were observed to be very small.