Industrial/Transsonic Centrifugal CompressorCopyright: © RWTH Aachen | IST
The FVV centrifugal compressor test rig was built in collaboration with the Forschungsvereinigung Verbrennungskraftmaschinen e. V. (FVV) and was put into operation in April 2016. Since then, all research projects have been technically supported by the FVV working group "Centrifugal Compressors".
The centrifugal compressor test stand is located in a closed room of the machine hall, which is surrounded by sound-absorbing cladding and a reinforced concrete shell approx. 30 cm thick. It is an open test stand where atmospheric air is drawn in through a filter box.
The transition to the DN400 intake pipe section is formed by an ISA-1932 inlet nozzle, which is used for mass flow determination by means of a differential pressure measurement. Following the direction of flow, there is a low-reflection termination to attenuate the sound radiation from the compressor on the suction side. The air is drawn in axially by the centrifugal compressor stage, compressed and fed through a spiral housing into the discharge line. Upstream of the compressor inlet is a variable guide vane, which can impart a pre-vortex to the impeller inlet flow and, depending on the vane angle, shift the characteristic curve towards larger mass flows and higher pressure ratios or vice versa. At the end of the pressure line, the air is released back into the environment by a backpressure throttle system.
The throttle system consists of a main throttle and a fine throttle and is used to control the compressor pressure ratio. A quick-opening function ensures that the compressor is relieved of pressure within seconds when critical operating conditions, such as compressor pumping, are being investigated.
The stage is driven by a speed-controlled asynchronous motor with a rated power of 2 MW. This provides a maximum torque of approx. 12.7 kNm up to the rated speed of 1,500 min-1. With a transmission ratio of 17.92, the planetary gear enables a maximum compressor speed of 32,256 min-1. The drive speed and the torque of the centrifugal compressor are recorded telemetrically, among other things, by means of a high-speed torque measuring hub.
The other infrastructure includes a redundant oil supply system with a controlled oil/water cooler and an oil heater. This system ensures lubrication of the planetary gearbox and the plain bearings of the centrifugal compressor.
The entire drive system and the test rig infrastructure are controlled and monitored by a programmable logic controller. With the aid of this and numerous sensors, automatic operational monitoring of the compressor is possible, which in the event of a serious fault can shut down the entire test stand safely.
The sound power radiated into the discharge line represents an important part of the sound emissions of a centrifugal compressor. Precise knowledge of the sound field at the compressor outlet is required to determine this sound power and for the optimum design of secondary sound insulation measures. For this purpose, a novel measuring method was developed and installed on the test rig, with which the sound power in the discharge line can be determined by means of 16 wall-flush, transient pressure sensors distributed in an optimized arrangement over the circumference of the discharge line. The measurement method was validated by experimental investigations and is now being transferred to other applications of centrifugal compressors.
In current research projects, both partial load instabilities and additional loss mechanisms due to a non-optimal fitting spiral casing are investigated. Partial load instabilities are investigated by examining phenomena such as rotating instabilities and detachments, determining the surge limit and frequency, and using the data to develop, validate, and improve predictive models for these phenomena. The variable guide vane provides an increased map width and, in particular, extends the part-load range with lower mass flows. The inlet swirl is typical of industrial compressors and favors flow instabilities.
Due to the numerous applications of centrifugal compressors, a standardization of components has become established. This includes not only the impeller, which can be scaled within a certain range, but also the volute casing. This means that a non-optimal match between this and the rest of the stage is already accepted in the design phase. In addition, the scroll housing for a speed line is only optimally flowed at one operating point, so that a detailed knowledge of the additional loss mechanisms is essential for the efficient and at the same time flexible operation of centrifugal compressors.
The test rig thus offers ideal conditions for conducting industry-oriented research.
A. Fassbender, M. Enneking, P. Jeschke. "Rotor-Alone Tones in the Outflow Noise of a Centrifugal Compressor." Proceedings of the ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. Volume 2B: Turbomachinery. Phoenix, Arizona, USA. 17.–21.Juni , 2019.
M. Mosdzien, M. Enneking, A. Hehn, D. R. Grates, P. Jeschke. "Influence of Blade Geometry on Secondary Flow Development in a Transonic Centrifugal Compressor." Journal of the Global Power and Propulsion Society 2, Auflage 1, Seiten 429-441, 2018.
A. Hehn, M. Mosdzien, D. R. Grates, P. Jeschke. "Aerodynamic Optimization of a Transonic Centrifugal Compressor by Using Arbitrary Blade Surfaces." Proceedings of the ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. Volume 2C: Turbomachinery. Charlotte, North Carolina, USA. 26.–30. Juni 2017.
M. Enneking, S. Behre, F. Fruth, P. Jeschke. "Intentional Adjustment of Excitation Source Phasing-Physical Interpretation of Axial Gap Variation." In Proceedings of the 14th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines, ISUAAAT14 (I14-S6-1). 2015.