Digital Particle Image Visualization of the Cooling Film Formation in a Flow Around the Leading Edge of a Vane in a Gas Turbine Engine

Velocity fields measured in the vicinity of the perforated leading edge of a turbine nozzle vane using the particle image visualization technique are presented. Noncontact measurements were performed in a plane segment consisting of three nozzle vanes and having an optically transparent inlet section offering visual access to the region of the leading edge of the central vane for a high-speed camera and to the laser sheet. The experimental investigations were performed at a fixed incoming flow velocity of 33 m/s, and the relative air flowrate through the cooling holes varied from 1.6 to 6.4%. The cooling film flow near the leading edge was visualized for three models of vanes differing in the air supply method to the holes, hole diameter, and number. Supply of the coolant to the cooling holes from one cavity resulted in a high degree of nonuniformity in the distribution of the film over the leading edge, which was caused by a high blowing ratio for the jets injected through holes located closer to the suction side. The experimental results have revealed that separate supply of cooling air to the holes on the pressure side, leading edge, and suction size minimizes sensitivity of the formed film thickness to the relative flow rate of the coolant and provides a more uniform distribution of the coolant over the vane surface in a wide range of the blowing ratio for the jets that varies from 0.5 to 2.5. Visualization has demonstrated extensive unsteadiness of the film flow along the vane airfoil. In this case, the cooling jet fed through the central hole oscillates, thereby leading to periodic formation of a film on either the pressure side or the suction side.