| In this experimental study, the value of introducing film cooling flow ahead of a gas turbine system first stage vane row is evaluated. A test facility is constructed to simulate the first stage nozzle of a high-pressure gas turbine. Upstream of the test section is a combustor simulator, which matches the velocity and turbulent levels and scales of an actual combustor. The test section consists of a three-vane, two passage linear cascade with modern airfoil shapes. One test section endwall is flat, while the other has contouring in the streamwise direction. Contouring starts upstream of the airfoil leading edge and ends at the airfoil trailing edges. Film cooling is introduced upstream of the airfoils through the contoured endwall via a single row or two rows of slots, some configured slots, and discrete holes. Secondary flow patterns and film cooling flow movement and mixing are studied by measuring three components of the velocity field using hot-wire anemometry and by measuring the temperature fields using a traversing thermocouple. For the thermal measurements, the film cooling flow is heated above the main flow temperature and dimensionless temperatures are recorded in the coolant-main flow mixing zone at different axial planes. Four cases of different film cooling to main flow mass flow ratios are documented. At low cooling flow rates, it is shown that more coolant emerges from the slot near the airfoil suction sides than near the airfoil pressure sides. Coolant emerging from the slot near the pressure side of the airfoil is carried with the endwall secondary flows towards the suction side of the adjacent airfoil. At higher momentum flux ratios, coolant emerges from the slots more uniformly than with low momentum flux ratios, and pressure side cooling is improved. Based on this knowledge, the slots are re-configured by partially blocking them to re-distribute the coolant flow towards the airfoil pressure sides. This uses the secondary flow to carry coolant towards the suction side of the adjacent airfoil. With this re-configuration, specific design criteria like improved cooling near the leading edge or better uniformity of cooling across the pitchwise direction can be satisfied. |
