The hot gas in mainstream can ingest into the stator-rotor wheel space through the working clearance between the rotating and stationary parts of a turbo machine. To avoid ingestion, a certain amount of compressor air is injected into the cavity. On one hand, it can lead to a significant loss of engine efficiency, so the injected air coming from the compressor should be as little as possible. On another hand, when the rim sealing flow enters the passage, strong interaction happens between the rim sealing flow and the secondary flow structures. The rim sealing flow adversely affects the aerodynamics of the mainstream flow.
The authors have designed a contoured slot seal (CSS) configuration and found this configuration has better sealing performance than uniform slot seal (USS) configuration. However, the effects of rim sealing flow on the flow field in the turbine blade passage with a contoured slot seal (CSS) configuration is unknown. Hence an experimental study is carried out to investigate the effects of rim sealing flow on the performance of a turbine cascade passage with different kinds of rim seal configurations and some suggestions about rim seal design are put forward.
The tests were performed in a linear turbine cascade in Beihang University. The flow field at 10% chord downstream from the turbine blade trailing edge was measured by a mini five-hole probe. Three different rim seal configurations are investigated: (1) uniform slot seal (USS) configuration, (2) contoured slot seal configuration with small seal clearance at the leading edge of the blade (CSS_S), and (3) contoured slot seal configuration with large seal clearance at the leading edge of the blade (CSS_L). The configuration without cavity is studied as the baseline case. This experiment investigated the effects of the rim sealing flow on the flow field of the linear cascade at four different rim sealing flow rates.
Results show that when there is no rim sealing flow, the existence of seal clearance makes the passage vortex in the blade root weaker for USS and CSS_L than that for the configuration without cavity. With the increasing of the rim sealing flow, the passage vortex is enhanced and moves towards the middle span for USS and CSS_S. For all of the rim sealing flow, the passage vortex intensity of CSS_L is weaker than that of USS and CSS_S. The rim sealing flow has the smallest effect on the performance of the turbine cascade for CSS_L. Based on the better feature of CSS_L, a new CSS configuration is proposed.
Experimental studies of the working processes of a reciprocating hybrid power machine with a slot seal of step-type with various working fluids
