Effect of non-axisymmetric contouring on performance and film cooling of a rotating turbine endwall subjected to the secondary air purge: A combined numerical and experimental study

Applying a new non-axisymmetric endwall contouring technology introduced by Turbomachinery Performance and Flow Research Laboratory (TPFL) at Texas A&M University to the second rotor row of a three-stage research turbine has shown that for a single rotor row a major turbine efficiency improvement can be achieved. Motivated by these results, numerical and experimental investigations were conducted to determine the effect of non-axisymmetric contouring on the endwall film cooling behavior of a rotating turbine row. To accomplish the film cooling, the endwall of the first rotor row is chosen for the contouring. It is subjected to the secondary air exiting from a large cavity through a circumferential slot that is inclined at 25° and impinges on the contoured hub. Performing Reynolds averaged Navier–Stokes (RANS) simulations by using the boundary conditions from the experiments, aerodynamics, performance, and film cooling effectiveness studies were performed by varying the injection blowing ratio and turbine rotational speed. Performance measurements were carried out within a rotational speed range of 1800–3000 r/min. The corresponding computational fluid dynamic simulations were carried out for four rotational speeds, 2000, 2400, 2600, and 3000 r/min. Comparison of the RANS aerodynamics simulations with experiments reveals noticeable differences. Considering the film cooling effectiveness, major differences between experiment and numerical results were observed and discussed in the paper.