EFFECT OF WAKE ON ENDWALL FILM COOLING EFFECTIVENESS FOR A ROW OF CYLINDRICAL HOLES NEAR THE STAGNATION REGION OF AN AIRFOIL

Over the last decades, researchers have investigated many aspects of film cooling. The present study investigates the effect of transition wake near the stagnation region on endwall film cooling effectiveness. Experimental measurements are presented for a single row of cylindrical holes inclined at 35 degrees with hole length to diameter ratio, L/D = 7.5, pitch to diameter ratio, PI/D - 3 with a constant density ratio of 1.26 and with nitrogen as the coolant. Nine different configurations were studied, The airfoil was positioned at x/D equal to (I) 6.4, (II) 12.7, and (III) 25.4. Configuration (IV-VI) consisted of the airfoil positioned at x/D = 6.4, 12.7 and 25.4 and a wake plate positioned at x/D=-12.7, upstream of the injection point. The presence of wake is also investigated on configuration VII through IX Configuration (VII-IX) consisted of the airfoil positioned at x/D - 6.4, 12.7 and 25.4 and a wake plate positioned at x/D-50.8, upstream of the injection point.. Configuration 0, 0-b and 0-c are the baselines; these configurations consist of a single row of cylindrical holes with and without wake plate. In the absence of wake, the average effectiveness increases with increasing blowing ratio at a x/D further downstream of the injection point where the jet has reattached. Higher blowing ratio increases lateral spreading of the jet promoting jet to jet interaction and mainstream interaction enhancing mixing. The presence or wake promotes jet mixing with the mainstream resulting in faster decay or film cooling effectiveness. Effectiveness is higher for the cases where the plate is placed further upstream of the injection point.