Windage sources in smooth-walled rotating disc systems

This paper presents experimental data and an associated correlation for the windage resulting from a disc rotating in air, characteristic of gas turbine engines and relevant to some electrical machine applications. A test rig has been developed which uses an electric motor to drive a smooth bladeless rotor inside an enclosed pressurised housing. The rig has the capability of reaching rotational and throughflow Reynolds numbers representative of a modern gas turbine. A moment coefficient has been used to allow a non-dimensional windage torque parameter to be calculated and agreement with the relevant data in the literature has been found within 10 %. Infrared measurements have been performed which allow direct surface temperatures of the rotating disc to be obtained. Laser Doppler Anemometry measurements have been made which allow velocities in the flow field of the rotor-stator cavity to be examined and tangential velocities corresponding to rotationally and to radially dominated flow conditions are shown. The importance of the flow regime in relation to the resulting windage has been identified and in particular it is noted that windage is a function not only of the ratio of rotational and radial flow dominance as defined by the turbulence parameter, but also, for a given value of the turbulence parameter, the magnitude of the rotationally induced and superimposed flows. The experiments extend the range of data available for windage in rotor-stator systems and has been used to produce a correlation suitable for applications operating up to the range Re φ = 107. Keywords: Windage heating; rotating flows; Internal air system