Particle Deposition in Gas Turbine Blade Film Cooling Holes

The aerodynamic processes leading to film cooling hole blockage have been investigated experimentally in large scale models of idealized internal cooling passages. The experimental scaling included reproducing engine cooling passage and hole Reynolds numbers together with a new dimensionless group which was matched experimentally to ensure that the measured particle trajectories were engine representative. It has been possible to achieve correct dimensional scaling with particles one thousand times larger than engine size. Simple visualization of the particle trajectories showed concentrations of impact locations inside holes normal to and inclined to the cooling passage surface. No attempt was made to model interaction between the particles and the passage walls. A new instrument has been developed to measure the concentration of particle impacts. Use of the device provides a fast and convenient way of measuring particle impact distributions. The regions of high impact concentration are consistent with blockage structures found in engines after service. The process of internal blockage of film cooling holes has been shown to be due to inertia driven particles of the order of 1 micron in diameter. Flow conditions immune from impact concentration and hence the blockage process have been identified for the inclined film cooling hole.