Actuation and Control of a Moveable Geometry System for a Full-Scale, Multi-Stage Centrifugal Compressor Test Vehicle

In recent years, several papers have been written regarding the use of moveable geometry systems to enable the rotation of otherwise stationary vanes used in centrifugal compressor research test vehicles. These systems typically are installed in single stage rigs or are placed at the inlet of the first stage of multi-stage centrifugal compressor test vehicles. This paper describes the capabilities of a state-of-the-art test vehicle that was developed by the Original Equipment Manufacturer (OEM) as a result of the OEM’s ongoing Research and Development Program aimed towards the implementation of novel and advanced technologies during the development of high-performance centrifugal compressors. The test vehicle is equipped with a variety of internal instrumentation that allow the collection of detailed aero/thermodynamic inter-stage performance data that is used to evaluate the behavior of the machine. The design of the unit also incorporates moveable vanes at the inlet guides upstream of each impeller, at each diffuser inlet and at the inlet of each return channel. The moveable geometry components allow infinite tuning of these components in a multistage environment, which allows the optimization of the aerodynamic performance of the stages based on design and/or off-design operating requirements of the process. The variable geometry system also allows the vanes to be positioned in such a way as to maximize the operating range of the compressor. The incorporation of adjustable vanes into the test vehicle allowed the OEM to significantly reduce the test cycle time, while maximizing the test data that was obtained from a single build. The positioning of the moveable vanes is controlled by a PC-based system that has been integrated into the OEM’s data acquisition system. This paper presents the work executed during the specification, design and implementation of the moveable geometry control system that was developed for the test vehicle. It covers topics such as the selection of the actuators and control hardware, as well as the integration of the actuators with the moveable vanes and other test unit components. Also discussed are the specification and development of the control software and the techniques, hardware and procedures used for the calibration of the moveable geometry system. The calibration was required to accurately determine the transfer function between the actuator movement and the actual rotation of the vanes. The paper also discusses the use of 5-hole pressure probes during the actual test to measure the flow direction upstream of the moveable vanes and how this information was used to achieve the test objectives. Finally, sample test data is presented to illustrate the impact that the moveable geometry system had over the performance of the compressor stages.