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.
In the present study, standard RANS and LES simulations are compared for two different film cooling configurations (The “777-shaped hole” experimentally investigated by Schroeder and Thole as well as the NEKOMIMI-shaped film cooling hole). The local distribution of the adiabatic film cooling effectiveness and flow phenomena are discussed. Based on the observations, the explanation for the superiority of the NEKOMIMI compared to simple fan-shaped film cooling holes is revised. Distinct differences with respect to flow phenomena can be observed depending on the simulations model. The results show that the impact of the horse-shoe vortex has been strongly underrated in the past and that it is not visible in the results of RANS simulations. Studies based on RANS can consequently lead to wrong conclusions.
With the LES simulations it is possible to resolve the small flow structures and have deeper insight into the development and dissipation of secondary as well as tertiary flow structures. The paper shows that such structures have a crucial impact to the local film cooling effectiveness downstream of the film cooling hole and lead to a wider spread-out of the coolant.
- Dickhoff, Jens (B&B-AGEMA GmbH)
- Schneider, Michael (B&B-AGEMA GmbH)
- Kusterer, Karsten (B&B-AGEMA GmbH)
- Bohn, Dieter (RWTH Aachen University)
- Horiuchi, Takeshi (Kawasaki Heavy Industries, Ltd)
- Fukuda, Mei (Kawasaki Heavy Industries, Ltd)
- Dr.-Ing. Karsten Kusterer, Managing Director