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978-3-8439-0359-2, Reihe Thermodynamik
A Contribution to Gas Turbine Combustor Cooling Using Complex Configurations
160 Seiten, Dissertation Universität Stuttgart (2011), Softcover, A5
The demands to modern gas turbines regarding efficiency and emission reduction increase continuously. In order to achieve the requirements, higher turbine inlet temperatures are demanded. This means simultaneously that more efficient cooling concepts are needed to protect highly stressed gas turbine parts. In combustor liners, convective backside cooling techniques have replaced film cooling approaches due to the possibility of implementing lean-premixed combustion. Additionally, a larger percentage of the compressed cooling is used in the combustion process. Due to the high Reynolds numbers and characteristics of the cooling configurations used in combustor liners, the existing correlations and results from studies conducted for internal turbine blade cooling aren’t sufficient to predict the heat transfer augmentation and the pressure loss correctly. For this reason, extensive experimental and numerical simulations under realistic combustor liner conditions are necessary.
In the present work, cooling configurations with ribs as main convective cooling features are investigated regarding heat transfer augmentation and pressure loss at high Reynolds numbers (ReD = 90, 000 − 500, 000). Rib parameters like dimensionless rib height e/Dh, dimensionless rib spacing P/e, rib angle of attack α and rib complexity (number of chevron s in W-shaped, 2W-shaped or 4W-shaped rib configuration) are varied to investigate how they influence the Nusselt number ratio and the friction factor in the cooling channel. Furthermore, the channel aspect ratio is varied and the cross section is partially blocked with the aim of investigating how the flow field behaves in cooling channels with geometrical constraints such as mounting rails or clamps. Also combinations of various convective cooling elements (ribs of different heights, hemispheres and dimples) are analysed regarding the friction factor and Nusselt number ratio.
For the heat transfer investigation, thermochromic liquid crystals are employed for the transient local wall temperature measurement, upon which the heat transfer coefficient and hence the heat transfer augmentation can be obtained. The friction factor is measured using pressure taps along the channel sidewall in a section, in which the flow is fully developed.
The numerical visualisations supplement the experimental results and help understanding the physical mechanisms and correlations between flow structures and heat transfer enhancement.