System influence on the surge behaviour of a centrifugal compressor

Authors

Alberto Serena  - Norwegian University of Science and Technology, Norway
Lars Eirik Bakken - Norwegian University of Science and Technology, Norway

Abstract

The flow unsteadiness in turbomachines, presenting a characteristic behaviour, requires a deep understanding of the underlying flow fundamentals, a careful analysis through advanced experimental methods and a clear distinction on how the surrounding system might lead to instabilities. These impact both system stability and machine reliability. As presented in previous publications, this study is part of a broader research activity at the Norwegian University of Science and Technology – Energy and Process Engineering Department – comprising the study of the impeller stage capabilities, transient flow regimes, erosion, surge instabilities and the electric motor drive control and monitoring. A literature review, with a particular focus on the system influence, experimental method, test rig layout, and instrumentation when handling with reverse and pulsating flow, is presented, providing an overview of previous and similar approaches. The evaluation of the system influence on compressor behaviour during surge and the best testing approach to describe the unsteady area without introducing further instabilities are specifically addressed. The main investigations include: -        Effect of discharge volume -        Effect of the location of flow-meter in the test loop for a prompt detection of flow reversal -        Stresses on machine: overheating and vibrations A particular care has been given to tuning instrumentation, so as to properly handle with transient conditions. This provides very useful guidelines for a clear setting of test procedure and key parameters measurements to detect unsteady phenomena under transient conditions, with instrumentation available for field operation and separating compressor behaviour from system response. The experimental technique is employed and described in detail in this paper, while performance modeling validation, object of parallel studies, will be presented in future publications. The test facility allows the required responsive dynamic measurements; tests are performed covering a broad range of flow rates, over three different rotational speeds. The focus area is on the rapid cycles across the zero-flow axis. The results presented in time and frequency domains show the evolution of the most relevant parameters during the surge and reverse flow phenomena and play a key role for the simulation of more complex dynamic scenarios. This provides a wide collection of test data of great value for a further understanding, the development of more reliable surge onset prediction models and control strategies.