Session: 10-04-01: Fluid Measurements and Instrumentation

Paper Number: 112735

112735 - Experimental Characterization of a Centrifugal Compressor in Second Quadrant Operation 

Instabilities in turbomachinery operation may be originated by the intrinsic flow unsteadiness, sudden variations of operating conditions, and the interaction with the surrounding system. All impact both system stability and machine reliability.

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.

A sustained or deep surge condition might force a centrifugal compressor into second quadrant operation, where higher pressure and flow pulsations occur, even if this stable reverse flow may be tolerated. Reverse flow can occur intermittently during surge cycles or continuously as a result of system malfunction or fast ESD with low inertia machines.

In this unusual backflow operating area, compressor system wise, the pressure – flow relation is often modelled with a simple approach, as a passive, valve-like component. Aerodynamically wise, some authors have implemented corrections taking into account specific phenomena, as incidence losses and blockage, starting from the velocity triangles at the impeller outlet. A deeper understanding of the underlying flow mechanisms is needed to properly model the compressor characteristic. These challenges benefit from the optical access made possible in the test rig on key areas, as the impeller inlet and outlet, allowing flow visualization.

In similar research, a booster compressor is forcing the flow to be stable in reverse flow. The instrumentation might be rotated according to the different expected flow direction. In this study, reverse flow is provided by the air flow release from a pressurized tank, representing a tuneable compressor discharge volume as well as process equipment malfunction, i.e., check valve failure or leakage.

This research, performed at the Norwegian University of Science and Technology by the Thermal Turbomachinery Research Team, involves a centrifugal compressor specifically designed to handle with a liquid fraction.

The test matrix covers a range of discharge pressures, back flow rates and rotational speeds, both at constant-imposed speed and with no torque applied, at locked or free shaft, to investigate the effect of different parameters and phenomena.

The results document the single stage compressor second quadrant characteristics under different operating conditions. The key contribution of this investigation is a collection of relevant and reliable data measurement, which lays an important foundation for further development of dynamic models for compressor system behaviour and allows to properly reduce complexity of surge protection devices, for operation in more favourable conditions.

Presenting Author: Alberto Serena Norwegian University of Science and Technology

Presenting Author Biography: Alberto Serena is a renewable energy professional (Master’s, PhD and MBA) with a 10-year experience in the value chain creation and management of innovation initiatives in academia, multinational and small-medium enterprises, across different sectors. Currently part of the Thermal Turbomachinery Research Team at the Norwegian University of science and Technology, holds a specific expertise on off-design performance of electric and fluid machines for energy conversion

Authors:

Alberto Serena Norwegian University of Science and Technology
Lars Eirik Bakken Norwegian University of Science and Technology