Optical analysis of the deposition and detachment phenomena experienced by an airfoil leading edge

Solid micro-particle ingestion is one of the principal degradation mechanisms in compressor sections. In industrial applications, micro-particles not captured by the air filtration system cause fouling and, consequently, a performance drop. Even if, in the last decade, manufacturers have been oriented to the development of transonic axial compressors, subsonic stages are commonly used for heavy-duty industrial applications such as pump stations and process compressors thanks to their very high reliability and relatively restrained cost (maintenance and recovery). This works presents an analysis of the deposition and detachment phenomena experienced by an airfoil leading edge. The experimental tests are carried out using micro-particles and two flow velocities. A non-contact continuous measurement process has been realized to discover the over-the-time modification of the deposit build-up and detachment that characterized the leading edge region. The measuring process is based on the image capture of the blade surface, comparing two subsequent frames, and recognizing the light intensity variation. Using such a strategy, this method generates a history of modifying the light intensity pixel by pixel. A recursive process has been highlighted after an initial phase representing the evolution of the surface condition from clean to fouled operating condition. Guidelines for interpreting the fouling behavior of a blade profile are proposed.