Aerodynamic performance measurements of a fully scaled, film-coated, turbine stage

Abstract

The MIT Blowdown Turbine short duration test facility was used to experimentally measure the aerodynamic performance of a film-cooled turbine stage. Turbine torque, speed, mass flow, temperature, and pressure were measured and used to calculate efficiency. Pressure ratio, corrected speed, and coolant mass flow were varied parametrically over a range of conditions and compared to a baseline. No distinct trend was seen in the pressure ratio tests. Efficiency increased approximately 2.2% with a corrected speed increase of 20%. This trend is a result of a corresponding decrease in blade loading. An efficiency decrease of 2% was shown for a two-fold increase in coolant mass flow. A preliminary comparison to a previous uncooled test series showed a 2% decrease in efficiency with a 12% coolant-to-mainstream mass flow ratio. To complete these tests, an uncooled turbine configuration was modified to a film-cooled configuration. A solid blade and nozzle guide vane set was machined via electro-discharge machining, laser drilling, and laser welding to provide film-cooling holes and manifold channels. The effective area (CdA) of the film-cooling holes was measured and part-to-part variations quantified. A coolant feed system was constructed to provide coolant flow to the turbine. Flow to the rotor blades, nozzle guide vanes, and tip casing was metered and controlled independently. Thick walled, squared edged, choked orifices were used. A set of experiments were performed to show that supersaturated coolant flow could be adequately controlled by this method.