Shroud heat transfer measurements inside a heated multiple rotating cavity with axial throughflow

Experimental measurements of heat transfer are made from the inner peripheral surface of a rotating test rig designed to be similar to a gas turbine high pressure compressor internal air system. The test rig comprises a number of annular discs sealed at their periphery by a shroud. An axial throughflow of cooling air enters the test rig and flows through the annular section between the disc bores and a central shaft. Tests were carried out for the following range of rotational speeds and axial throughflow rates: 540 < N-R < 10,800 rev/min and 0.124 < m < 0.85 kg/s (corresponding to the range of rotational and axial Reynolds numbers 4 x 10(5) < Re-phi < 7.7 x 10(6) and 3.3 x 104 < Re-z< 2.2 x 10(5)). The shroud Nusselt numbers are found to depend on the shroud Grashof number. They are relatively insensitive to changes in axial Reynolds number and two geometrically similar cavities give similar values of Nusselt number. The heat transfer from the shroud is governed by the mechanism of free convection. It is recommended that a modified form of a correlation for Rayleigh-Benard convection in a gravitational force field be used, with appropriate modification, to predict shroud heat transfer. (C) 2007 Elsevier Inc. All rights reserved.