Accurate numerical prediction of surface heat transfer in the presence of film cooling within aero-engine sub-components, such as blade effusion holes and combustor liners, has long been a goal of the aero-engine industry. It requires accurate simulation of the turbulent mixing and reaction processes between freestream and cooling flow, in particular the potentially unsteady nature of the jet as it emerges from the hole, and this can require a high degree of spatial and temporal resolution. On the other hand, attempting to resolve all the details in the flow field can be computationally demanding for industry, therefore many researchers have developed hybrid turbulence models to scale-resolve the mixing zone using Large Eddy Simulation (LES) but model the remaining boundary layers with a Reynolds-Averaged Navier Stokes (RANS) model.

 

In this study, one such hybrid, scale-resolving turbulence model, the Stress Blended Eddy Simulation (or SBES) model, is used, which uses a blending function to automatically switch between RANS and LES based on the local flow features. This can significantly reduce the computational cost compared to a full LES simulation. This SBES model is then used in conjunction with the Flamelet Generated Manifold (or FGM) combustion model and a commercial finite-volume CFD code to compute the surface heat flux on a flat plate, which refers to an experimental rig built at MIT (Kirk D. R. 2003. "Near-wall reaction effects on film-cooled surface heat transfer''. PhD thesis. Massachusetts Institute of Technology.). The flat plate is brushed by a uniform freestream of argon with ethylene seeded inside, and is cooled by either reacting air or non-reacting nitrogen jet inclined at 35 degrees to the freestream. Calculations are performed firstly for an un-cooled flat plate to obtain the heat flux correlation, and then for both reacting and non-reacting jet cooling cases across a range of jet-to-stream mass flow ratios (or blowing ratios), and compared with the experimental data. The effects of mesh resolution are also investigated. Calculations are also performed across a range of Damkohler number (i.e. flow to chemical time ratio) from zero to 30, with unity blowing ratio, and the differences in the maximum surface heat flux magnitude in the reacting and non-reacting cases at a specific location downstream of the hole are investigated.

 

Results from these analyses show good correlations with the experimental data upstream and downstream of the cooling hole. The results also show that the degree to which the heat flux is captured accurately in the area immediately behind the hole is largely affected by the spatial resolution of the mesh. Results from the Damkohler number sweep also show a good match with the experimental data across the range investigated.


SBES/FGM Simulation of Film-Cooled Surface Heat Transfer and Near-Wall Reaction

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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