Endwall Film Cooling Through Fan-shaped Holes with Different Area Ratios

The present paper reports on the aero-thermal performance of a nozzle vane cascade, with film cooled endwalls. The coolant is injected through four rows of cylindrical holes with conical expanded exits. Two endwall geometries with different area ratios have been compared. Tests have been carried out at low speed (M=0.2), with coolant to mainstream mass flow ratio varied in the range 0.5-2.5%. Secondary flow assessment has been performed through 3D aerodynamic measurements, by means of a miniaturized 5-hole probe. Adiabatic effectiveness distributions have been determined by using the wide banded thermochromic liquid crystals (TLC) technique. For both configurations and for all the blowing conditions, the coolant share among the four rows has been determined. The aerothermal performance of the cooled vane have been analyzed on the basis of secondary flow effects and laterally averaged effectiveness distributions; this analysis was carried out for different coolant mass flow ratios. It was found that the smaller area ratio provides better results in terms of 3D losses and secondary flow effects; the reason is that the higher momentum of the coolant flow is going to better reduce the secondary flow development. The increase of the fan-shaped hole area ratio gives rise to a better coolant lateral spreading, but appreciable improvements of the adiabatic effectiveness were detected only in some regions and for large injection rates.