Flow and Heat Transfer in Rotating Compressor Cavities With Inverted Shroud-Throughflow Temperature Differences

In a gas turbine engine, cooling flow bled from the compressor is forced beneath the rotating discs holding the compressor blades. This causes heat to be exchanged with the disc shroud, which is heated by the compressed main gas path. Typically, the temperature of the throughflow is lower than the temperature of the shroud. The temperature gradient drives buoyancy effects within inter-disc cavities, which coupled with Coriolis forces results in an unsteady flow structure affecting disc temperature distributions and, in turn, disc growth and thermal stresses. However, certain cavities are exposed to the inverse scenario where the internal throughflow travels upstream and is therefore hotter than the shroud; this is typically found in low and intermediate pressure compressors. Understanding the effects of the inverted temperature difference on the flow and heat transfer is important for optimising engine design to increase operating efficiency. This paper presents a novel experimental investigation on the fundamental mechanisms affecting the flow structure and heat transfer in rotating cavities exposed to an inverse temperature gradient, with a heated cob region and cooled shroud. An isothermal cavity is also investigated to examine the effects of changing Rossby number on the cavity flow structure over a range of engine representative conditions. Temperature distributions, shroud heat flux and unsteady pressure measurements are presented for steady-state and transient conditions ranging from negative to positive temperature difference.