1 Copyright © 2003 by ASME Proceedings of ASME Turbo Expo 2003 Power for Land, Sea, and Air June 16–19, 2003, Atlanta, Georgia, USA GT-2003-38140 FILM COOLING ANALYSIS USING DES TURBULENCE MODEL Subrata Roy and Sagar Kapadia Computational Plasma Dynamics Laboratory Kettering University, Flint, MI 48504 James D. Heidmann NASA Glenn Research Center Cleveland, OH 44135 ABSTRACT The complex dynamic nature of the spanwise vortices in film cooling of turbine blades makes it necessary to accurately model the flow field temporally and spatially using detailed simulation techniques like direct numerical simulation or large eddy simulation of turbulence. Although, the later requires less computational effort and thus can simulate flows at higher Reynolds number than direct simulation, both these methods remain very expensive. As a viable alternative, this paper presents a Spalart-Allamaras based detached eddy simulation (DES) that is applied to a film cooled flat plate for the first time. The numerical model uses an unstructured grid system to resolve the dynamic flow structures on both sides of the plate as well as inside the hole itself. Detailed computation of a single row of 35 degree round holes on a flat plate has been obtained for blowing ratio of 1.0, and a density ratio of 2.0. The DES solution is also benchmarked with Reynolds averaged Navier- Stokes formulation for the same blade-hole configuration. The comparison shows that the DES simulation, which makes no assumption of isotropy downstream of the hole, greatly enhances the realistic description of the dynamic mixing processes. INTRODUCTION In a variety of industrial applications the interaction of cool air jets with hot crossflow becomes important. Examples include vertical takeoff and landing (V/STOL) engineering and film cooling of gas turbine blades. Systematic investigation of such flowfield started in late 50s. Jordison [1], Fearn and Weston [2], Moussa, et al. [3], Andreopoulos and Rodi [4] studied isothermal jets into crossflow. For thermal flows, the resulting temperature downstream of the jet, the trajectory and physical path of the jet are critical design parameters. Specifically, the blades/vanes in propulsion gas turbine engines require film cooling to protect the airfoils from thermal stresses caused by exposure to hot combustion gases. The problem becomes aggravated by the growing trend to use higher turbine inlet temperature for better engine performance. Figure 1 shows the schematic of a single round jet injected in the crossflow at an angle. This geometry is very appropriate for the turbine engine community and has been extensively studied for cooling performance for a wide range of blowing ratio (i.e., momentum ratio of injected air to crossflow). These results show details of the vortex interaction region, and mixing and mean centerline species concentration decay in the near and far field. Goldstein [5] summarized early studies in the area of film cooling. These studies were based on slot flows, and f ilm cooling effectiveness values were found to correlate well with the parameter x/Mb, where x is the downstream distance, M is the blowing ratio, and b is the slot width. This parameter has also been used for discrete hole cooling, with b defined as the effective slot width for the row of holes. However, the physics of discrete hole cooling is quite different from that of a slot. A row of discrete holes typically has a much lower span averaged downstream film effectiveness distribution for the same x/Mb due to the formation of vortices which allow hot gas to penetrate to the wall. These vortices are of the scale of the hole size, so if a numerical simulation has a spanwise grid spacing greater than the film hole spanwise pitch, as is typical for turbine blade aerodynamic design, their effect is lost. In essence, any such calculation is two-dimensional on the scale of the film holes. Numerical investigations of jets based on integral methods were done by Vizel and Mostinskii [6], Chen [7] and Adler and Baron [8] initially. These models were essentially idealized models. A number of numerical models have also been proposed that approximated the three-dimensional vortex sheet by a two-dimensional one to predict details of the flowfield [7]. However, the mixing of a jet in a cross-stream is a fully three- dimensional phenomenon (Moussa et al. [3], Fric and Roshko [9], Smith and Mungal [10]), and thus such idealized treatments lack accuracy. Numerical solutions of the full Navier-Stokes equations have also been used to obtain detailed solutions in