UNE ANALYSE NUMERIQUE DU REFROIDISSEMENT PAR IMPACT RENFORCEE PAR UN FLUX TRANSVERSAL A L’AIDE D’UN TURBULATEUR EN FORME DE U

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Kurzfassung

The turbine inlet temperature and the compression ratio are the main drivers for the thermodynamic efficiency of a gas turbine. Effective cooling of the first turbine vanes allows the gas temperature to exceed the softening point of the turbine material. Impingement cooling offers an efficient usage of cooling air in order to obtain high heat transfer rates. In some impingement cooling systems, the coolant creates a self-induced cross-flow for the adjacent jets. The cross-flow deflects the jet and disturbs the stagnation region, which leads to a reduced heat transfer on the hot surface. Geometrical features on the hole or target plate upstream of the jet can be used to shield the jet from the incoming cross-flow. In this study an alternative approach is taken and a U-shaped turbulator is installed downstream of the jet hole. This arrangement uses the cross-flow to reinforce the jet by guiding it into the adjacent jet and thus increasing its effective jet Reynolds number. Compared to a smooth channel configuration, the Nusselt number on the target can be increased by 5-16% without a significant change in the pressure loss. This is a purely aerodynamic effect and is not caused by increasing the area of the heat exchanging surface. A numerically investigated configuration is derived from an existing experimental impingement cooling test facility. The geometry represents a generic impingement cooling configuration with a row of nine inline impingement jets, with a diameter of D = 0.0152m. All jets are influenced by a self-induced cross-flow. The jet-to-plate spacing as well as jet pitch are set to 5D , the jet Reynolds number is 10, 000 and the curved U-shape ribs are installed downstream of the jet on the hole plate. The Reynolds Averaged Navier Stokes (RANS) simulations are performed with the DLR in-house solver TRACE and the SST turbulence model. Experimental data sets from the literature, with and without turbulators, are used as validation case for the CFD. The results show a satisfactory agreement between the simulations and the experiments. The effects of different jet-to-plate spacing, jet Reynolds number as well as rib height, position and shape are investigated numerically. The effectiveness of the U-shaped turbulator is discussed in combination with additional turbulators (from the literature) on the target plate that increase the heat exchanging area. Presented results contain local, area and line averaged values of the Nusselt number on target as well as hole plate, the velocity, and the vorticity. This paper concludes with a best practice guide for the usage of the U-shaped turbulator in gas turbine cooling designs. A discussion of the manufacturability by Selective Laser Melting is included.

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• UNE ANALYSE NUMERIQUE DU REFROIDISSEMENT PAR IMPACT RENFORCEE PAR UN FLUX TRANSVERSAL A L’AIDE D’UN TURBULATEUR EN FORME DE U. (deposited 11 Dez 2023 10:34) [Gegenwärtig angezeigt]