A Computational Technique to Evaluate the Relative Influence of Internal and External Cooling on Overall Effectiveness

Abstract

Abstract Gas turbine hot gas path components are protected via coolant that travels through internal passageways before being ejected as external film cooling. Modern computational approaches facilitate simulation of the conjugate heat transfer that takes place within turbine components, allowing prediction of the actual metal temperature, usually nondimensionalized in the form of the overall effectiveness. Efforts aimed at improving cooling are often focused on either only the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are inextricably linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. The relative influence of internal cooling, external cooling, and convection through the film cooling holes on overall effectiveness is not well understood. Computational fluid dynamics (CFD) simulations were performed in order to isolate each cooling mechanism, and thereby determine their relative contributions to overall effectiveness. The conjugate CFD model was a flat plate with five staggered rows of shaped film cooling holes. Unique boundary conditions were used to isolate the cooling mechanisms. The internal cooling was modeled with and without heat transfer on the internal surface in order to isolate the effects of plenum cooling. Convection through the coolant holes was isolated by making the inside of the film cooling holes adiabatic. This was done in order to evaluate the influence of the internal cooling provided by the cooling holes themselves. The effect of film cooling was removed through the novel use of an outlet boundary condition at the exit of each hole that allowed unaltered internal coolant flow without external coolant ejection.