Investigations of Trenched Film Hole Orientation Angle on Film Cooling Effectiveness

Abstract The effect of altering the orientation angle of trenched film hole on film cooling effectiveness (ƞ) is analyzed through numerical investigation. The film holes were oriented at 6 different angles viz., 0°, 30°, 45°, 90°, 135° and 180° with a fixed inclination angle 30° and with a pitch to diameter (P/D) ratio 5.The length and depth of the trench embedding the film hole are fixed at 3D and 0.75D respectively. Three different blowing ratios M=0.5, 1 and 1.5 were studied. Results from the study reveal that changing the orientation angle of film hole with in trench offered a considerable improvement on ƞ from near film hole region to far downstream location on test surface. For a low blowing ratio of 0.5, the film cooling effectiveness distribution changes with respect to film hole orientation angle and higher ƞ zones are distributed along the corresponding film hole orientation angle. The film hole oriented at 90° with respect to stream wise direction delivered highest ƞ at all three different blowing ratios due to better lateral spreading and uniform coverage of injected coolant. Except near film hole region, 30° and 45° hole orientation produced uniform lateral effectiveness compared to 0° hole orientation.