The improvement of the overall performance and efficiency of gas turbines, especially in the internal cooling air system is of general interest. This requires the reduction of pressure losses induced by vortices and secondary flow. The steady state effects are known from literature and experiments. But also pressure fluctuations and oscillations e.g. resonances have an impact on the efficiency of the internal cooling air system. These unsteady effects are only principally discussed in the literature. Experimental investigations of pressure fluctuations and oscillations in rotating cavities, which are part of the internal air system, are very rare. One reason might be given by the fact that the investigation of these unsteady effects is a technical challenge especially for higher rotational speeds. This paper presents a new rotor test rig with a telemetric measurement system which permits time-resolved pressure measurements in the cavity. The cavity dimensions are similar to those of a real industrial gas turbine. The design of the test rig and the telemetric system allows rotational frequencies up to 10000 rpm. The current experimental investigation is focused on pressure fluctuations and oscillations in rotating cavities with through flow and their dependency on the test parameters. The aim is to find out the relevant effects for operation and design optimisation of rotating cavities in gas turbines. The rig consists of a stationary air delivery and an axial air transfer interface between the stator and the rotor. The rotor contains one cavity. The interface acts as a flow chopper. The air is blown from the stator drillings to the rotating inlet holes of the rotor which provide the connection to the cavity inside the rotor. The rotating holes pass the stator holes periodically, causing pressure fluctuations in the cavity. The frequency of the fluctuations depends on the rotational frequency of the rotor and the number of inlet and stator drillings, which can be varied. The tests are carried out for a range of the parameter Reφ, calculated with the outer radius of the cavity, up to 1·106 and for different mass flow rates. The new test rig, the setup, the instrumentation and the first measurements are the topic of this paper. The non-stationary effects found in the cavity and their dependency on the parameters rotational frequency and mass flow will be discussed and compared with known theoretical approaches.

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