This paper discusses experimental results from a two cavity test rig representative for the internal air system of a high pressure compressor. Thermal steady state measurements of the time-averaged local heat fluxes on both sides of the mid disc are presented for three different flow regimes: pure axial throughflow of cooling air and axial throughflow of cooling air in two directions with a superposed radial inflow of hot air in one cavity. Mass flow ratios between 1/40 < mrad/max < 2/1 are measured. Tests were carried out for a wide range of non-dimensional parameters: Re φ up to 107, Rez up to 2 × 105 and Cw up to −2.5 × 104. In all cases the shroud is uniformly heated to approximately 100°C. The local axial heat fluxes are determined separately for both sides of the mid disc from measurements of the surface temperatures with open spot-welded thermocouples. The method of heat flux determination and an analysis approach calculating the uncertainties and the sensitivity are described and discussed. The local heat flux results of the different flow paths are compared and interpreted by assumed flow structures. The time-averaged heat flux results can adequately be interpreted by flow structures of two toroidal vortices for axial throughflow and a source-sink flow for the radial inflow. The measurements show that the axial heat flux can change the direction, i.e. areas exist where the disc is heated and not cooled by the flow. For axial throughflow a local minimum of heat flux exists on the impinged side in the range of x = 0.65 if the axial Reynolds number is low or the rotational Reynolds number is high. On the back side a heating area exists in all tests in the lower half of the disc (x < 0.6) due to recirculated air of higher temperature. This heating area corresponds to the range of the inner vortex and increases with higher axial and rotational Reynolds numbers.

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