出口导向叶片的沉积研究

ABSTRACT An experimental facility was fabricated to simulate particle deposition on the internal wall of a nozzle guide vane cooling cavity. The facility supplied particle-laden flow at temperatures up to 540°C to a simplified impingement cooling test section. The heated flow passed through a perforated film hole plate and impacted on the internal surface of a vane wall. The particle-laden impingement jets resulted in the buildup of deposit cones associated with individual impingement jets. The deposit growth rate increased with flow temperature and when the film hole plate temperature was elevated with backside heating. At low temperatures, deposit formed not only as individual cones, but as ridges located at the midplanes between impinging jets. The base diameter of the deposit structures were found to be larger than the impingement hole diameter due in part to an aerodynamic lensing effect. Further studies using a test piece with optical access were used to document the evolution of deposit cones during continuous deposition. INTRODUCTION The expansion of aircraft traffic into developing countries has caused a significant portion of fleets to fly in areas of less than desirable air quality. This is a trend that will only increase in upcoming decades as developing areas such as parts of Asia and Africa will require more of the commercial market. Poor air quality can lead to ingestion of particulate into the engine. Ingestion of particulate can cause erosion of the compressor blades and deposits on both the internal and external surfaces of turbine vanes and blades. The internal passages are especially sensitive to these deposits due to their small geometries. Internal cooling schemes such as impingement cooling force air and particles to directly impact the internal surface making it more likely for deposits to form. Figure 1 shows a representative vane cross-section with film hole plates to help increase the internal heat transfer. Deposition in internal cavities poses an added thermal risk compared to external deposition. While deposition on the external surfaces of turbine vanes is problematic due to increased surface roughness, restricted flow, and other
Proceedings of ASME Turbo Expo 2014: Turbine Technical Conference and Exposition GT2014 June 16 – 20, 2014, Düsseldorf, Germany
GT2014-27150
PARTICLE DEPOSITION IN INTERNAL COOLING CAVITIES OF A NOZZLE GUIDE VANE - PART I: EXPERIMENTAL INVESTIGATION C. Clum*, E. Bokar, B. Casaday, J. P. Bons Department of Mechanical and Aerospace Engineering Ohio State University Columbus, OH 43235 aerodynamic losses, the presence of the particulate can potentially be thermally beneficial to the surface in that it insulates the material with its lower thermal conductivity. Deposition in internal cavities has the opposite effect, insulating the vane wall from the coolant flow, thus leaving the vane unprotected from the hot flow. These deposits can cause a decrease in coolant flow and subsequent increase in material temperatures, reducing paME
noticeable deposition would result. The cutoff temperature for external deposition varies depending on the composition of the particulate, but the lowest published threshold temperature is 960 oC [3]. Even the highest coolant temperature used in the experiments of Walsh and Cardwell et al. (700 oC) was well below what would be considered a typical threshold temperature for external deposition. Experimental studies by Bonilla et al. [4] and computational studies by Barker et al. [5] have shown that particle size has a first order effect on deposition rate. This is because the size of the particle for a given flow field determines its Stokes number, which is correlated with the probability of that particle hitting the surface. Therefore, knowing the correct particle size for a given flow field is essential. A study performed by Dunn [6] on a gas turbine engine illustrated that while large particles may enter the engine, once they have passed through a few compressor stages the mass median diameter (MMD) of the particles was 7 µm. This study looks at the effects of particle size, temperature, and mass flow rate on deposition in a simulated turbine internal cooling deposition rig. EXPERIMENTAL FACILITY The Accelerated Internal Deposition Rig (AIDR) was designed to simulate the deposition that occurs in a nozzle guide vane (NGV) leading edge cavity that uses impingement cooling. Accelerated deposition is based on the idea that if net particle weight is matched and particle-particle interactions are minimal, then similar characteristics should be present between two tests with different particle to air volumetric ratios. Accelerated deposition allows experiments to be conducted in a laboratory on a much shorter timescale than they occur in real life. This idea was supported by Jensen et al. [7] for external turbine deposition. A schematic of the AIDR facility can be seen in Figure 2.