Effect of space-chord ratio on the endwall flow in a large deflection turbine rotor cascade with tip clearance

Results obtained from an experimental study of the endwall and blade tip surface static pressure flow field of a large deflection linear turbine cascade are presented for various tip clearance levels and space chord ratios. In addition, endwall flow is visualised and the results presented. For zero clearance, the primary and secondary separation lines are observed with two saddle points. The interaction of the endwall and blade boundary layer is significantly affected by the presence of tip clearance. The formation of horse - shoe vortex was not observed at higher tip gaps indicating that pressure forces have dominating influence than the viscous forces. The size of the tip clearance vortex increases with the tip gap height. The origin of the tip clearance vortex separation line moves upstream with the increase in space - chord ratio. Due to the area contraction caused by the tip separation vortex, the fluid moving towards the tip gap from the pressure side is accelerated. Downstream of the separation vortex, the endwall pressure increases due to flow mixing. The mixing is incomplete in the aft portion of the blade. The passage vortex in the present investigations did not diminish with increase in clearance. The discharge coefficient is low near the leading and trailing edge regions.