In modern gas turbines, film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). Within the past decade, the technology has been improved step by step at B&B-AGEMA and Kawasaki Heavy Industries Ltd.; mainly by means of numerical simulations. The laterally averaged film cooling effectiveness is typically captured with acceptable accuracy, but the experimental measurements still show a deviation from the numerically obtained results with respect to the local film cooling effectiveness distribution behind the film cooling hole. Nevertheless, the film cooling air spread out in the lateral direction is one of the keys for enhancement of the film cooling performance. Thus, more precise simulations are consequently necessary for improvement of the hole shape configuration.
The present study involves simulations of a baseline fan shaped hole configuration (“777 hole” investigated by Schroeder and Thole [1][2]) using different turbulence models available in STAR-CCM+ with isotropic and anisotropic turbulence consideration (constitutive relations). Distinct differences with respect to flow phenomena (detachments and vortex creation) can be observed depending on the applied turbulence model. In total, the results show that anisotropic viscosity strongly influences the film cooling performance prediction by CFD for prediction of the film cooling effectiveness, but none of the models provides acceptable accuracy in this regard.
In modern gas turbines, the film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). As a result, the cooling air remains close to the wall and spreads in lateral direction along the surface. The ACRV result from the specialized shape of the expanding hole exits (NEKOMIMI-shape). Thus, the design parameters have a crucial impact to the film cooling effectiveness behind the hole.
In the present study the design parameters are varied and in order to explore the design space for a defined test case with respect to the maximum achievable averaged adiabatic film cooling effectiveness. This illustrates the capabilities of the technology. Additionally, the design space of a laidback fan-shaped film cooling configuration is explored and compared to the result obtained with the NEKOMIMI-shaped geometry. In order to show the robustness of the configurations with respect to compound angles of the cross flow, two advanced configurations — one NEKOMIMI and one shaped hole — are analysed with compound angles up to 16°.
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