Magnetic Resonance Imaging Techniques for Measuring Film Cooling Flow Velocity and Effectiveness

Film cooling of gas turbine engine components directly influences the efficiency and lifetime of the engine. Prediction of the film cooling surface effectiveness remains a problem area for engine designers. Magnetic Resonance Imaging (MRI) measurements of the surface film cooling effectiveness can be made using the analogy between temperature and passive scalar concentration in which the concentration of scalar marked cooling fluid is measured as it mixes with the main flow. The present work specifically addresses refinements to MR imaging techniques needed to accurately measure the concentration of a scalar contaminant at a flow-bounding surface. Anecdotal data are presented from experiments in which a single film jet exits into the boundary layer on one wall of a square channel. Data are presented for hole angles α = 30° and 60° and blowing ratios BR = 0.5 and 1.0. The Reynolds number of the main channel based on hydraulic diameter and bulk velocity is 400,000 and the jet Reynolds number at BR = 1.0 is 5300.