Leading Edge Film Cooling and the Influence of Leading Edge Wedge Angle at Design and Off-Design Conditions

Transient liquid crystal experiments have been carried out to measure the adiabatic film cooling effectiveness and heat transfer characteristics of leading-edge film cooling for two different configurations at design and off-design incidence angle. The two models, representative of the leading edge of turbine blades, are symmetrical blunt bodies with two different leading edge wedge angles. Film cooling is introduced from two rows of cooling holes, representative of a pressure-side row and a suction-side row. The measurements show that incidence angle changes have less influence on the location of the stagnation line for larger wedge angle. In the present film cooling situations, the heat transfer is heavily increased at the holes locations compared to the baseline situations. The increase is more important for cooling holes located further from the stagnation line. It was found that the adiabatic film cooling effectiveness of cooling holes located in such an accelerated main flow does not improve when the blowing ratio increases. Indeed for the model with more downstream cooling holes and a larger wedge angle, the local adiabatic film cooling effectiveness is even reduced with increased blowing ratio. For the model with the smaller wedge angle and the cooling rows located more upstream, at off-design conditions an important stagnation line shift leads to the undesirable situation where both rows are blowing on the same side (case 1). For larger wedge angles and cooling rows located more downstream, the stagnation line stays in-between the two rows even at off-design conditions. The row closer to the stagnation line may then exhibit a homogeneous spanwise film cooling distribution with a rather high adiabatic film cooling effectiveness in spite of a reduced coolant flow (case 2).