Session: 12-10 Film Cooling with Thermal Barrier Coatings

Paper Number: 80810

80810 - Conjugate Heat Transfer of Cylindrical and Trenched Film Cooling Designs With Array Jet Impingement 

The efficiency of gas turbines can be improved by increasing the gas temperature at the turbine inlet. Hence, for the last decades research improvements in cooling of the turbine vanes have been sought. Various film cooling designs have been tested to improve the external cooling of the vane surface. In most computational studies the adiabatic film cooling effectiveness is investigated due to simplicity. The standard design to apply film cooling are discrete round holes which tend have a low adiabatic efficiency, especially at higher blowing ratios (e.g. > 0.6) due to jet lift off the vane wall. Trenched film cooling designs showed higher adiabatic film cooling efficiency even for large blowing ratios. Experimental investigations of Davidson et al. 2021 on an experimentally simulated turbine vane with thermal barrier coating (TBC) underlined this finding. Trenched film cooling designs lead to higher film cooling effectiveness at the external surface of the TBC. However, at the interface between the TBC and the metal surface of the vane the effect on the temperature was almost negligible. This makes the use of more complex film cooling designs questionable. In the mentioned study, no impingement cooling was used additionally. In the experimental study of Jung et al. 2017 a flat plate experiment was conducted with impingement cooling and several rows of standard round holes for external film cooling. Various Biot numbers were tested. The impingement cooling showed to offset the overall efficiency to higher values if compared to a case without jet impingement. Moreover, several film cooling rows are simulated in the spanwise and axial direction which allowed to see the variation of the film cooling efficiency along those directions.

In our numerical study including conjugated heat transfer (CHT) and array jet impingement we want to use the literature case of Jung et al. 2017 to calibrate the CFD simulations using the (steady) RANS equations. Afterwards we run simulations of the same set-up, however applying two trench designs to the existing test case. The first trench set-up is a tight transverse trench design and the second set-up is derived from an optimized trench design. We want to investigate the effect of cylindrical and trenched film cooling applications onto the overall film cooling efficiency by testing different blowing ratios, adiabatic assumptions as well as different Biot numbers by adding a solid domain to the CFD simulation. Since this set-up contains several rows of film cooling holes with a trenched design, impingement cooling as well as CHT it differs from other numerical publications in the view of the authors. In previous studies RANS models like the k-omega SST model have shown to be limited in predicting the performance of film cooling efficiency. Furthermore, RANS models applied to studies with jet impingement have shown to be limited on its own, too. Thus, we are interested to see how the results of our CFD simulations compare to the case of Jung et al. 2017. In addition, we want to see how the impingement on the backside of the cooling holes affects the resulting flow fields of the trenches. One may conclude afterwards if a more complex RANS simulation involving TBC with vane typical Biot numbers could lead to the same conclusion as in Davidson et al. 2021.

Davidson, F. Todd, David A. Kistenmacher, and David G. Bogard. “Film Cooling With a Thermal Barrier Coating: Round Holes, Craters and Trenches,” 2012, 12. Proceedings of ASME Turbu Expo

Jung, E. Yeop, Heeyoon Chung, Seok M. Choi, Ta-kwan Woo, and Hyung H. Cho. “Conjugate Heat Transfer on Full-Coverage Film Cooling with Array Jet Impingements with Various Biot Numbers.”, 2016 Experimental Thermal and Fluid Science 83 (May 2017): 1–8. https://doi.org/10.1016/j.expthermflusci.2016.12.00

Presenting Author: Lukas Fischer Universität der Bundeswehr München

Presenting Author Biography: Lukas Fischer studied aerospace at the TU Berlin from 2011 to 2018. During this time experience was gained at the Department of Fans and Compressors at Rolls-Royce Deutschland, the Institute of Fluid Dynamics at the TU Berlin and the Department of Aerospace at the University of Arizona. Since April 2018 the author is a research associate at the Universität der Bundeswehr München focusing on numerical simulations of innovate film cooling geometries with realistic external turbulence.

Authors:

Lukas Fischer Universität der Bundeswehr München
Andrés Felipe Sánchez Porras Institut für Thermodynamik, LRT – 10
Fabian Schleich Institut für Thermodynamik
Fabian Feller Institut für Thermodynamik
Richard Raffelt Institut für Thermodynamik
Michael Pfitzner Institut für Thermodynamik LRT-10