Eddy simulation of turbine blade trailing edge cooling

We study mixing in the slot jet cooling channels of the trailing edge of a turbine blade. Modern turbofan engines have turbine inlet temperatures about 1,700K. This is higher than the melting point of turbine blade material. The state of art cooling technique over the exterior blade surface is film cooling. Cooling air flows through many small holes and slots to form a thin shield, protecting the surface from very hot gas in the ambient stream. Film cooling at the trailing edge of a turbine blade is achieved by pumping the coolant through a break out from the pressure side of the blade.; It has been found previously that cooling of the trailing edge does not perform as effectively as has been predicted. There appears to be an 'anomalous' mixing phenomenon that carries hot gas to the blade surface.; Unsteady Reynolds averaged (RANS) simulations suggest that the mixing is related to coherent vortex shedding, but they fail to predict the film cooling effectiveness. They are unable to explain the anomalous mixing; indeed their failure is the source of the puzzle. We use eddy simulation to study the origin of anomalous mixing. The particular form of eddy simulation in the present study is Scale Adaptive Simulation (SAS). This is often referred to as a hybrid RANS-eddy simulation method.; Flow over a generic trailing edge, break out geometry was computed. The block structured, MPI based, SuMB code was modified for this purpose. A non-dissipative convection scheme was added, along with a filtering method to stabilize the eddy simulations. The SST-SAS model was implemented. An appropriate turbulent inflow was created.; Due to complexity of the geometry, a grid of 54 computational blocks was created. The correct level of film cooling effectiveness was predicted by the simulations. The spectrum of fluctuations contained a peak corresponding to coherent vortex shedding, in addition to broad band turbulence. Away from the wall unsteady RANS and eddy simulation produced similar levels of mixing. The mixing anomaly is associated with a layer near the wall. The coherent shedding made a large contribution to the unsteady energy, which did not occur in the RANS computations. It appears the vortices are shielded from the wall layer, unless they are distorted by three dimensional disturbances. Those distortions occur in the eddy simulation and allow the coherent unsteadiness to penetrate the wall layer.