This contribution presents the experimental results of telemetric heat transfer measurements on the rotor side of an open rotor-stator system air gap with various rotational speeds and rotor-stator distances. For the heat transfer measurements, the local over-temperature method is used, which is based on the analysis of the non-stationary temperature rise of small heated structures at the rotor surface. Additionally, experiments on a second test rig, a flat plate connected with an axial fan, are conducted for the streamwise calibration of the sensors. The measurement program is composed of eight rotational speeds n between 76 and 8,558 rpm at five gap distances s in the range from 1.5 mm to 25 mm at eight radial sensor positions r between 46 and 188 mm. Overall the test rig installation is equivalent to a rotational Reynolds number range Rer from 1,085 to 2,040,000. An evaluation and interpretation of the results shows that the characteristic correlation between the Reynolds number and the Nusselt number is similar to that used for the turbulent flow at a free rotating disc. The variation of the gap distance leads to a constant offset in the heat transfer coefficient, which becomes significantly higher with small distances.

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