Abstract
Diffusion-shaped film holes with compound angles are currently being investigated for high temperature gas turbine airfoil film cooling. An accurate prediction of the coolant blowing rate through these film holes is essential in determining the film effectiveness. Therefore, the discharge coefficients associated with these film holes for a range of hole pressure ratios is essential in designing airfoil cooling circuits. Most of the available discharge coefficient data in open literature has been for cylindrical holes. The main objective of this experimental investigation was to measure the discharge coefficients for subsonic as well as supersonic pressure ratios through a single conical-diffusion hole. The conical hole has an exit-to-inlet area ratio of 4, a nominal flow length-to-inlet diameter ratio of 4, and an angle with respect to the exit plane (inclination angle) of 0°, 30°, 45°, and 60°. Measurements were performed with and without a cross-flow. For the cases with a cross-flow, discharge coefficients were measured for each of the hole geometries and 5 angles between the projected conical hole axis and the cross-flow direction of 0°, 45°, 90°, 135°, and 180°. Results are compared with available data in open literature for cylindrical film holes as well as limited data for conical film holes.
Highlights
Diffusion-shaped holes are commonly used in film cooling of the gas turbine airfoils
The discharge coefficients associated with these film holes for a range of hole pressure ratios is essential in designing airfoil cooling circuits
Figure 4 shows the variation of the discharge coefficient for the straight-through cylindrical hole geometry with the ratio of upstream plenum total pressure to the downstream static pressure
Summary
Diffusion-shaped holes are commonly used in film cooling of the gas turbine airfoils. The purpose for employing such holes is to reduce the coolant velocity at the film hole exit in order to Discharge coefficients associated with many orifice geometries and flow conditions have been under investigation by many researchers These investigators include Rohde et al (1969) who performed an experimental study of discharge coefficients for flow through thick plate orifices with the approaching flow perpendicular or inclined to the orifice axis. Parker and Kercher (1991) introduced an enhanced method to compute the compressible discharge coefficient of thin and long orifices with inlet corner radiusing based on the presented data in open literature This method accounts for compressibility, inlet corner radius, orifice length, and Reynolds number. They concluded that inlet radiusing and chamfering increases the discharge coefficient substantially. Hay et al (1994) measured
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