Hydraulic seals are successfully used to seal gas turbine shaft and bearing chambers because of their main advantages: reliable operation with zero leakage. However, due to the temperature limitations of the lubrication oil their application has been limited to relatively cold areas in the engine (e.g. front bearing chamber). To employ hydraulic seals in hotter areas, particularly at the rear bearing chamber with elevated wall and air temperatures, oil degradation and coking must be taken into account. Therefore, recirculation zones which lead to hot spots must be avoided and the oil residence time must be reduced. A new seal design that enforces a defined flow pattern through the seal (Bo¨ck, U.S. Patent No. 6,568,688B1) claims to keep oil temperature below degradation limits even in hotter operational environments. However, the circumferential velocities and oil levels in the seal are altered, which must be considered in the design process. This paper compares the flow characteristics of the classic and advanced seal design. Analytical calculation approaches for both seal designs are presented. The commercial software FLUENT was used for numerical simulations, applying the ‘Volume of Fluid’ (VoF) method. To validate the numerical and analytical results, a configuration was tested experimentally in a two shaft co-rotating set-up, which was especially designed for hydraulic seals. Good agreement could be achieved in a comparison of the monitored oil levels in the seal for different engine relevant shaft speeds and pressures.

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