A Centrifugal Compressor - System Transient Digital Twin

Abstract Off-design operation in turbomachinery entails several critical issues. The intrinsic flow unsteadiness is amplified by transients and interactions with the surrounding system, with detrimental effects on stability and components reliability. In this paper, a description of the transient behaviour is achieved as a combination of theory, laboratory experiments, operational experience, data analysis and process simulation. This benefits from a responsive test rig, allowing the modification of layout and key parameters, as an inadequate test procedure might strongly affect the overall behaviour and transient evolution. Results are presented over a wide test matrix, including surge volume size and rotational speeds. These data are vital for a full compressor-system digital twin. Among the main outcomes, are the establishment of the actual surge margin and a suitable recovery strategy, achieved by the necessary early detection. The main focus area is the validation of the system model prediction of the trip trajectory, caused by severe voltage grid disturbance, or variations in inlet composition, or downstream pressure build-up. Tuning the model on experimental performance data is needed for reliable and faithful reproduction of real behaviour and interaction, as it would otherwise account only for overall degradation, not taking into account the intrinsic unsteadiness, flow channels unevenness, turbulence responsible for instabilities onset and evolution. Results indicate the importance of ensuring reliable data acquisition and analysis, with adequate instrumentation range, accuracy, synchronization, responsiveness and positioning, so as to tune the model and provide closure to the predictions.