An Active Phantom Cooling Concept for Turbine Endwall Cooling From Pressure-Surface Film Coolant Injection

Cooling of the endwall of a nozzle guide vane should receive special attention due to its uniqueness of near-wall complex secondary flows and concomitant challenge of offering film-coverage for cooling the endwall pressure-side corner regions. The use of internal enhanced cooling at the endwall backside could be an option, but it increases manufacturing cost, adds weight to the component, causing excessive pressure losses in the secondary air system. Novel film cooling concepts are, therefore, required to provide effective cooling for these difficult-to-cool regions. This study proposes an active cooling concept effected by placing a row of film cooling holes on the vane pressure surface near the endwall with the intention of utilizing second-order cooling (or phantom cooling) from pressure-surface film-coolant injection to provide increased cooling effectiveness and enlarge the area of coverage on the endwall. The effects of hole diameter, injection angle, and compound angle, as well as coolant injection rate are investigated. Detailed phantom cooling effectiveness over the endwall is documented using pressure-sensitive paint (PSP). To provide a description of the flow physics driving the cooling process, computational modeling is carried out to qualitatively document mixing of coolant with the freestream flows and further to qualitatively evaluate heat transfer changes caused by the pressure-surface film injection. Experiments show that significant cooling occurs in the endwall pressure-side corner and extends beyond the passage throat. Higher coolant injection rates and an optimized pressure-surface injection geometry maximize endwall phantom cooling. An effectiveness correlation for the active cooling is developed to provide a straightforward tool for designers to apply in turbine design.