In this paper a numerical investigation of conjugate heat transfer of a cooled combustor wall will be presented. The focus lies solely on wall cooling in the region between outer annulus, inner annulus and parts of the hot gas path in the combustor.  The simulation model consists of a hot gas channel, a wall, and a coolant channel. The simulation is simplified by using a planar wall and scaled engine-like operating parameters. The thermal and fluid flow properties are scaled and adapted by using dimensionless quantities to match real conditions in an aero engine combustor. Particularly the hot gas velocity, coolant velocity, density ratio of coolant to hot gas, heat transfer coefficients, material conductivity and geometry were subject to scaling. To match the quantities influencing the conjugated heat transfer under experimental conditions, it was necessary to select suitable materials with matching thickness for the solids to keep Biot and Nusselt numbers. The model for this investigation is based on a test rig at the Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology in Karlsruhe.

As cooling methods, the combination of effusion cooling and impingement cooling is used. The geometry of the model is derived from real test specimens. The effusion cooled specimen is provided with laidback-fanshaped cooling holes with a 7-7-7 geometry. The cooling holes have an entrance diameter of E=sqrt(2)\*D with a reference diameter of D=4mm and are angled with alpha=30deg to the surface. The opening angle of the laidback and fanshaped part is 7 deg. The cooling holes have a repeating pattern with every fourth row. The lateral distance of each cooling hole is P = 10D with D=4mm and the streamwise distance is S = 6.67D. Each row the cooling holes is shifted by 1/3\*P to create the pattern.

The specimen with the impingement cooling holes has cylindrical cooling holes with a diameter of D=4mm and with an angle of 90 deg to the surface. The same pattern is applied to this specimen.

The distance between the two specimens is 5D and forms a cavity, where the coolant impinges the backside of the effusion specimen. Both specimens are arranged parallel to each other, but longitudinally and laterally shifted, so that the impinging flow covers the maximum available area between 4 effusion cooling holes on the coolant side.

Developing coolant flow patterns in the cavity will have an influence in the resulting heat transfer and the resulting total cooling effectiveness on the hot gas surface of the effusion specimen. Typical film-cooling quantities from the calculated results such as blowing ratio M, momentum ratio I, total cooling effectiveness eta, heat transfer coefficients, Nusselt numbers and Biot numbers will be derived, while varying the pressure loss across the combustor wall.


Numerical Investigation of Conjugate Heat Transfer in an Effusion and Impingement Cooled Combustor Wall

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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