EFFECTS OF VARYING TIP CLEARANCE AND AXIAL GAP ON AXIAL-FLOW TURBINE STAGE PERFORMANCE ( PRESENT STATE OF THE ART)

The leakage flow near the tip of rotor and stator blade rows of an axial-flow turbine stage imposes significant thermal loads on such blades. It is also responsible for the aerodynamic losses therein. This leakage flow is induced mainly by the pressure difference across the tip section for both the rotor and the stator. Most research has hitherto focused on the effect of varying the tip clearance ratio, but a rather little amount of published work on axial gap effect is found. This paper presents the outcome of scanning the available research on tip clearance and axial gap parameters and effects of their variation on the flow characteristics and performance of a typical axial–flow turbine stage. The prime objective here is to throw some light upon the state of the art in this area of research. The surveyed literature is discussed and criticized, giving suggestions for further investigation of the problem