Ebfog: Deposition, erosion and detachment on high pressure turbine vanes

Fouling and erosion are two pressing problems that severely affect gas turbine performance and life. When aircraft fly through a volcanic ash cloud the two phenomena occur simultaneously in the cold as well as in the hot section of the engine. In the high pressure turbine, in particular, the particles soften or melt due to the high gas temperatures and stick to the wet surfaces. The throat area, and hence the capacity, of the HP turbine is modified by these phenomena, affecting the engine stability and possibly forcing engine shutdown. This work presents a model for deposition and erosion in gas turbines and its implementation in a three dimensional Navier- Stokes solver. Both deposition and erosion are kept into account, together with deposit detachment due to changed flow conditions. The model is based on a statistical description of the behaviour of softened particles. The particles can stick to the surface or can bounce away, eroding the material. The sticking prediction relies on the authors' EBFOG model. The impinging particles which do not stick to the surface are responsible for the removal of material. The model is demonstrated on a high pressure turbine vane. The performance deterioration and the throat area reduction rate are carefully monitored. The safe-To-fly time through a cloud can be inferred from the outcome of this work as important piece of on-board information for the flight crew.