The Effect of Film Cooling on Nozzle Guide Vane Deposition

Abstract

An accelerated deposition test facility was used to study the relationship between film cooling, surface temperature, and particle temperature on deposit formation. Tests were run at gas turbine representative inlet Mach numbers (0.1) and temperatures (1090°C). Deposits were created from lignite coal fly ash with mass median diameters of 1.3 and 8.8μm. Two CFM56-5B nozzle guide vane doublets, comprising three full passages and two half passages of flow, were utilized as the test articles. Tests were run with different levels of film cooling back flow margin and coolant temperature. Particle temperature upon impact with the vane surface was shown to be the leading factor in deposition. Since the particle must traverse the boundary layer of the cooled vane before impact, deposition is directly affected by the film and metal surface temperature as well. Film coolant jet strength showed only minor effect on deposit patterns on the leading edge. However, larger Stokes number (resulting in higher particle impact temperature) corresponded with increased deposit coverage area on the showerhead region. Additionally, infrared measurements showed a strong correlation between regions of greater deposits and elevated surface temperature on the pressure surface. Thickness distribution measurements also highlighted the effect of film cooling by showing reduced deposition immediately downstream of cooling holes. Implications for engine operation in particulate-laden environments are discussed.