Influence of hole diameter and fan shaping on film cooling of a rotor blade endwall

This paper shows the influence of different hole diameters and of hole fan shaping on film cooling effectiveness of a rotor blade endwall. The investigation refers to a blade cascade of a high-pressure-rotor stage of a real gas turbine tested in a low speed wind tunnel. In the endwall models, hole diameter was increased from 0.7 mm of the original design to 1.0 mm. By this way it was possible to almost double the coolant flow rate, maintaining the same blowing ratio. Then, in the attempt to further improve film cooling effectiveness, a conical fan shaping was implemented in the cooling scheme. Endwall cooling scheme is realized through ten cylindrical holes distributed along the blade pressure side. Aerodynamic and thermal tests have been carried out at low Mach number (Ma2is=0.3) for each considered geometric configuration. Coolant-to-mainstream mass flow ratio has been varied in a range of inlet blowing ratios M1 from 0 to 4.0. A 5hole probe was traversed downstream of the trailing edge plane at the highest blowing rate, to evaluate if injected flow affects secondary flows. The thermal behavior was analyzed by using Thermochromic Liquid Crystals technique, so to obtain film cooling effectiveness distributions. The 1.0 mm hole diameter cooling scheme, compared to the one with 0.7 mm diameter holes, provided significantly higher adiabatic effectiveness for all the considered blowing ratios. A minor coolant flow rate (about 30% less) is enough to get a good overall adiabatic effectiveness. The introduction of fan shaped holes did not produce any significant improvement.