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.