Prediction of Film Cooling on Gas Turbine Airfoils

Abstract

A three-dimensional Navier-Stokes analysis tool has been developed In order to study the effect of film cooling on the flow and heat transfer characteristics of actual turbine airfoils. An existing code (Amone et al., 1991) has been modified for the purpose. The code is an explicit, multigrid, ceil-centered, finite volume code with an algebraic turbulence model. Eigenvalue scaled artificial dissipation and variable-coefficient implicit residual smoothing are used with a full-multigrid technique. Moreover, Mayle’s transition criterion (Mayle, 1991) is used. The effects of film cooling have been incorporated into the code in the form of appropriate boundary conditions at the hole locations on the airfoil surface. Each hole exit is represented by several control volumes, thus providing an ability to study the effect of hole shape on the film-cooling characteristics. Comparison with mid-span experimental data for four and nine rows of cooling holes is fair. The computations, however, show a strong spanwise variation of the heat transfer coefficient on the airfoil surface, specially when the shower-head cooling holes are on.

Leading Edge Film-Cooling Effects on Turbine Blade Heat Transfer

“…Viscous effects in the streamwise direction are neglected in comparison to those in the other two directions. Justification for this assumption is provided in Garg and Gaugler (1994). The multistage Runge-Kutta scheme developed by Jameson et al (1981) is used to advance the flow solution in time from an initial guess to the steady state.…”

“…The three-dimensional Navier-Stokes code of Amone et al (1991) for the analysis of turbomachinery flows was modified by Garg and Gaugler (1994) to include film cooling effects. Briefly, the code is an explicit, multigrid, cell-centered, finite volume code with an algebraic turbulence model.…”

“…Herein, we follow the analysis of Garg and Gaugler (1994) in order to study the effect of spanwise pitch of shower-head holes, and coolant to mainstream mass flow ratio on the adiabatic effectiveness and heat transfer coefficient on the film-cooled C3X vane with nine rows of film cooling holes including five rows on the shower-head.…”

“…While Leylek and Zerkle's approach is good to resolve the nearhole and within-hole physics, it cannot be extended to a real blade with hundreds of holes, at least with present-day computers. It can be used to feed the hole-exit information into a "middle-ofthe-road" approach taken by Garg and Gaugler (1994), wherein appropriate boundary conditions are imposed at the hole exits on the blade surface instead of resolving the coolant flow within the hole pipe. Garg and Gaugler's analysis provides proper resolution for accurate prediction of surface heat transfer coefficients, and is still computationally manageable for analyzing the whole blade with hundreds of holes.…”

“…They observed adjacent jet merging and a pronounced "stripping" pattern on the suction surface at low coolant flow rates, but at high coolant rates, the film-cooling flow followed a more spanwise trajectory resulting in a more uniform reduction in heat transfer at the vane surface. Garg and Gaugler (1994) modified the three-dimensional Navier-Stokes code of Arnone et al (1991) to include the capability of analyzing heat transfer on a film-cooled blade. They did not discretize the hole pipe but applied appropriate boundary conditions at the hole exit on the blade surface, representing each hole exit by several control volumes (about 20).…”