Abstract

The aerothermal characterization of film cooled geometries is traditionally performed at reduced temperature conditions, which then requires a debatable procedure to scale the convective heat transfer performance to engine conditions. This paper describes an alternative engine-scalable approach, based on Discrete Green's Functions (DGF) to evaluate the convective heat flux along film cooled geometries. The DGF method relies on the determination of a sensitivity matrix that accounts for the convective heat transfer propagation across the different elements in the domain. To characterize a test article, the surface is discretized in multiple elements that are independently exposed to perturbations in heat flux. The local heat flux augmentation is then used to estimate the sensitivity of the adjacent elements. The resulting DGF becomes independent from the thermal boundary conditions, and the heat flux measurements can be scaled to any thermal conditions given that non-dimensional numbers are maintained.

The procedure is applied to two different geometries, an uncooled and a film cooled flat plate with a 30 degree 0.125” cylindrical injection orifice with L/D of 6. First, conjugate 3D Unsteady Reynolds Averaged Navier Stokes simulations are performed to assess the applicability and accuracy of this approach. Finally, experiments performed on a flat plate geometry are described to validate the method and its applicability. Wall-mounted thermocouples are used to monitor the surface temperature evolution, while a 10 kHz burst-mode laser is used to generate heat flux addition on each of the discretized elements of the DGF sensitivity matrix.

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