Session: 10-06-01: Fluid Measurements and Instrumentation

Paper Number: 142703

142703 - A Centrifugal Compressor - System Transient Digital Twin 

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 system stability and components reliability. The compressor behaviour in the overall system under severe off-design conditions needs to be adequately modeled, so as to allow a faithful representation essential to predict the trajectories of transients in the instability area. Preliminary, parallel researches provided a deeper understanding of the underlying flow fundamentals.

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. The study benefits from a responsive test rig, allowing, in addition, modification of layout and key parameters, as a non adequate test procedure might strongly affect the overall behaviour and transient evolution.

Among the main outcomes of this study, are the establishment of the actual surge margin and of a suitable recovery strategy; in order to achieve these, an early detection is needed. The instrumentation placement, responsiveness and synchronization are paramount as any delay might impair an accurate detection of instability inception. A fast-acting valve is installed at the outlet so as to enable the simulation of rapid transients.

The main focus area is the validation of the system model, and, in particular, the study and prediction of the trip trajectory, especially caused by voltage dips, due to severe grid voltage disturbance, or variations in inlet composition, or, finally, downstream pressure build-up. The electric motor and drive, while having a large polar inertia, have a fundamental drawback in the quick power outage (with a decay in the order of 10 ms). The main limitations of relying solely on system modeling are related to the model not taking into account nor describing the intrinsic unsteadiness, flow channels unevenness, turbulence responsible for machine instability, while it rather accounts for overall degradation, and, therefore, experimental performance data are needed for reliable and faithful reproduction.

The experimental campaigns and data processing are presented, with a test matrix covering a wide range of parameters, including system layout and surge volume size, rotational speeds, flow rates ranging from nominal point down to fully closed valve operation. These data are vital for system modeling validation for a full compressor-system digital twin.

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 component and vprovide closure to the predictions.

Presenting Author: Alberto Serena NTNU

Presenting Author Biography: Alberto Serena's specific research experience has focused on off-design performance of electric and fluid machines for fluids processing, energy conversion and electric mobility

As a member of the Thermal Turbomachinery Research Team at the Norwegian University of Science and Technology, the main research topic is the study of flow unsteadiness and machine instabilities, based on experimental testing complemented by Computational Fluid Dynamics, Time-Frequency Analysis and System Modeling

Authors:

Alberto Serena NTNU
Ola Ilseth Pronk NTNU
Lars Eirik Bakken NTNU