Modelling of buoyancy-affected flow in co-rotating disc cavities

Research in rotational buoyancy-driven flow has shown that the flow within the compressor inter-disc cavities is highly three-dimensional and time dependent. Two approaches in the numerical modelling of the flow have been considered. One is to use 3D, unsteady CFD to model a single inter-disc cavity with axial throughflow. This is very computationally expensive. A second approach, adopted here, is to break down the complex flow process into separate physical mechanisms and introduce approximate but computationally efficient models for these processes. The aim is to produce a method that can be incorporated into current design practice. Two underlying flow mechanisms may be identified for this complex flow; the first associated with the flow within the inter-disc cavities and the second associated with the axial throughflow under the compressor disc bores. Using CFD, the modelling of these two underlying flow mechanisms has been combined and a steady axisymmetric modelling method has been developed. The technique has been applied to both a research compressor rig and to an actual gas turbine HP compressor rotor, and results have been compared to measured data