INFLUENCE OF INTERNAL PARALLEL AND V-SHAPED RIBS ON THE DISCHARGE COEFFICIENT OF A CYLINDRICAL FILM COOLING HOLE

An experimental study has been conducted investigating the discharge behaviour of cylindrical film cooling holes with the main focus on the effects of rib arrangement and crossflow velocity inside the internal cooling passage of a gas turbine blade. Two straight flow channels of rectangular cross-section simulate the crossflow situations present at the inlet and outlet of a film cooling hole. The two channels are connected by a single scaled-up film cooling hole with a diameter of 10mm, an inclination angle of 30 degrees and a length-to-diameter ratio of 6. Measurements have been performed at various internal crossflow Mach numbers and rib geometries for both, parallel and perpendicular orientation of internal and external crossflow. Parallel and V-shaped ribs with quadratic cross section and 4 different angles with respect to the internal crossflow direction (45 degrees, 60 degrees, 75 degrees and 90 degrees) have been placed upstream and downstream of the hole entrance at one wall of the cooling passage. The rib height equals the hole diameter, the rib pitch to height ratio is 10. The internal crossflow Mach number has been varied in a range between 0 and 0.37. The data show that placing ribs onto the wall of the coolant passage may result in reduced, unchanged, or even increased discharge coefficients. Internal crossflow Mach number and orientation of the coolant passage in respect to the hole axis have been identified as major influencing parameters.