Porosity-driven approaches to model fouling effects on flow field

Air contamination by solid particles represents a real hazard for compressors for both heavy-duty and aero-propulsion gas turbines. Particles impacting the inner surfaces of the machine can stick to such surfaces or erode them. The presence of deposits entails the reduction in performance of the machinery. As the severity of the problem increases, the performance reduction can become so big to demand engine shut-down and off-line washing. Numerical modeling is one of the techniques employed for tackling the fouling problem. In this work, an innovative procedure is proposed in order to evaluate the losses and the variation in the fluid flow due to the deposits. Specifically, as the deposit grows, it is assumed it forms a porous medium attached to the wall. The porosity of this zone (related to the packing of the particles and to the amount of particles that sticks in to a zone) is responsible for the deposition-induced losses. Different approaches to compute such losses are proposed and discussed. By using this methodology, the two main effects offouling (variation in roughness and in shape of the airfoil) can be easily included in a comprehensive analysis of the variation of the performance of the compressor over time. Furthermore, this approach overcomes the difficulties that may arise by using a mesh morphing technique. The computational grid is not modified and thus its quality is retained, without remeshing requirements, even for large deposits.