Effects of Flow Separation on a Highly Loaded, Low-Pressure Gas Turbine Blade at Low Reynolds Numbers

Abstract

Current gas turbine engines experience a loss in performance due to the low Reynolds number flow in the low-pressure turbine. This low flow speed can result in separation of the air from the blade surface, reducing the efficiency of the engine. The Baylor University Cascade wind tunnel (BUC) is being used to study this flow separation. A cascade wind tunnel contains a row of turbine vanes that simulates a turbine wheel. The BUC is capable of simulating the environment seen by the low-pressure turbine at high altitudes by producing Reynolds numbers varying from 25,000 to 400,000. The L1A blade profile is currently being tested. Coefficient of pressure (Cp) plots show a less than 1% difference between surface pressure locations when comparing the most inboard and outboard test blades. This agreement demonstrates the flow uniformity in the tunnel. Cp plots also compared favorably to the literature, validating the BUC operation and providing insight into how Reynolds numbers and free stream turbulence intensity (FSTI) affect flow separation. The literature and this study showed the size and reattachment of the separation bubble was highly dependent on the FSTI for lower Reynolds numbers (25,000 to 200,000). This comparison also showed that the size of the separation bubble and the location was not heavily impacted by FSTI for Reynolds numbers above 200,000. Tests in the future will be conducted to determine the actual FSTI of the BUC. Once completely validated, future studies with the BUC may include use of particle image velocimetry (PIV) to visualize the flow, a gold foil steady state technique using liquid crystals to measure heat transfer, and a series of deposition tests using surface roughness (sandpaper or textured sprays) to measure performance loss under these conditions. The ultimate goal of this research is to improve blade design in the low pressure turbine for all commercial and military aircraft.