<p>Modern gas turbine engines require film cooling to meet efficiency requirements. An integral part of the design process is the numerical simulation of the heat transfer to film cooled components and the resulting metal temperature. Industry design simulations are typically performed using steady Reynolds averaged Navier-Stokes (RANS) simulations. However, much research has shown limitations in the use of steady RANS to predict film cooling performance, which are typically attributed to turbulent mixing. Recent experiments measuring time-accurate film cooling jet behavior have indicated unsteady jet motion in sweeping and separation-reattachment modes contributes to the time-average dispersion of the cooling jet along the cooled surface. This study identifies the physical forces on film cooling jets issuing from fan-shaped holes, including acoustic resonance, which drive the unsteady behavior. Turbulent velocity fluctuations in the stream-wise direction cause corresponding fluctuations in the film cooling jet blowing ratio, resulting in a time-average deficit in film cooling performance beyond the steady behavior predicted with time-averaged blowing ratio. Since the observed film cooling jet motions originate in the hole, it is posited that the behavior is a feature of the supply geometry. In this way, plenum film cooling supply geometry is observed to act as a Helmholtz resonator. An unsteady RANS simulation including acoustic forcing is compared to experimental data along with a steady simulation to demonstrate the advantages of including the unsteady component of the Navier-Stokes equations.</p>

Coupling of Mainstream Velocity Fluctuations with Plenum Fed Film Cooling Jets

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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