Heat Transfer to an Actively Cooled Shroud With Blade Rotation

In this paper, an experimental study of the shroud heat transfer behavior and the effectiveness of shroud cooling under the conditions of rotation is undertaken in a single stage turbine at low rotation speeds. The shroud consists of a periodic distribution of cooling holes that are 1 mm in diameter (D). The holes are angled at 45 degrees in a repeating pattern consisting of 5 unique hole pitches around the shroud circumference. Measurements of the normalized Nusselt number and film cooling effectiveness are done using liquid crystal thermography. These measurements are reported for the no coolant case, nominal blowing ratios of 1.0, 1.5, 2.0, 2.5 and 3.0, and rotation speeds of 300, 400, 500, 600 and 700 RPM. The results with no coolant injection show that the high Nu/Nu0 region migrates upstream toward the shroud leading edge with increasing rotation. The cooling results show that increasing the blowing ratio increases the area-averaged film cooling effectiveness in the shroud hole region for all rotation speeds studied. Furthermore, increasing the blade rotation speed increases the area-averaged Nusselt numbers and decreases the area-averaged film cooling effectiveness in the shroud hole region for all blowing ratios studied. As in the no-coolant case, with increasing rotation speeds, the high Nu/Nu0 region migrates upstream toward the shroud leading edge and disrupts the cooling effectiveness in this region. Finally, the results show that decreasing the shroud coolant hole spacing changes the lateral heat transfer profile from a periodic sinusoidal distribution for a shroud hole spacing of P/D = 10.4 to a more even distribution for a smaller P/D = 4.8.