A Multiphase Pump Experimental Analysis
Doctoral thesis
Permanent lenke
http://hdl.handle.net/11250/2410476Utgivelsesdato
2016Metadata
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Sammendrag
This research project focuses on the characterization of the behaviour of a mixed-flow pump under
off-design conditions and two-phase operation, in terms of performance degradation and
instabilities. The recent multiphase pump models allow to process higher and higher amounts of
gas in variable operating conditions. An improved understanding of the fundamental physics is
therefore necessary, as, due to the concurrent physics involved and transient phenomena, a proper
machine characterization cannot be limited to an overall description of the performance, but rather
it needs to rely on advanced analysis tools revealing the local flow phenomena.
Multiphase flow affects turbomachines operation introducing secondary flows, unsteady
phenomena and other disturbances in the flow field. Besides influencing the whole system and
causing losses, these disturbances introduce additional issues as vibrations and alternating stresses
on the rotodynamic components, which can reduce the machine reliability. The detection of the
instabilities inception, a proper definition of the safe operation boundaries and the necessary actions
to recover stable operation when instabilities appear are of key importance to prevent shut-down
events and failures and ensure an extended components life.
The main goal of this investigation consists in the experimental description of the flow regimes in
the different performance map zones, aided by flow-visualization; focus is given to the recognition
of the flow mechanisms responsible for flow field modifications, which affect the machine
stability, and to the relation of the performance and stability variations to the originating
phenomena in the hydraulic channels.
In order to accomplish these objectives, a novel multiphase pump laboratory has been specifically
designed and built. An extensive literature review of the two-phase flow in turbomachines has
helped to include room for the necessary investigations and carefully assess their feasibility. The
laboratory facility allows a complete optical access to the pump channels and fine adjustments in
the inlet configuration and the tip clearance gap. Tests are performed over a wide range of machine,
flow and fluid composition parameters.
As to the investigation tools employed, local measurements of the main flow parameters and a
high-speed camera provide an interesting insight into the unsteady and transient flow phenomena.
The numerical tool capability is evaluated under single-phase conditions, while a thorough study
of the available two-phase flow simulation models and their experimental validation will be the
subject of future studies.
The influence of the operating parameters - pump speed, flow rates, mixture composition, suction
pressure - on the machine performance and operating range has been extensively studied and the
test results confirm most of the expected trends.
The original contribution of the current work has been the understanding of the flow mechanisms
and their connection to the outer measurements; this is very useful for a future development of a
control strategy in real machines
On a further stage of the research, it is desirable that the analytical description of the bubble flow
and the correlations describing the switch among different flow regimes be validated
experimentally for this specific application.
Two-phase flow, especially at unsteady conditions, introduces additional challenges which make
the use of advanced visualization techniques require a preliminary assessment, which is the object
of future studies. Along with image based metrology, these ones promise to provide a qualitative
description of the flow field.
The Doctoral Thesis is based on five research papers which present the main outcomes of the study
and are enclosed in the Appendix section. This report provides the necessary background, starting
from the literature study which has led to the choice of the research approach, together with a
presentation of the testing rig design and building, the experimental facility and procedure
description, the test results and the characterization of the main flow mechanisms involved. It
should be noted that, as the main focus is set on the flow visualization, the measurement of the
pump efficiency has not been prioritized. A preliminary assessment of the numerical simulation
tool is performed on single-phase operation. The Conclusion section presents a summary of the
findings accomplished within the timeframe of the current work, along with the suggestion of
further analyses and investigations for a deeper understanding of the flow phenomena and machine
behaviour.
Består av
Paper 1: Serena, Alberto; Bakken, Lars Eirik. Design of a Multiphase Pump Test Laboratory Allowing to Perform Flow Visualization and Instability Analysis. ASME 2015 Power and Energy Conversion Conference - Is not included due to copyright available at http://dx.doi.org/10.1115/POWER2015-49769Paper 2: Serena, Alberto; Bakken, Lars Eirik. Experimental Characterization of the Flow Instabilities of a Mixed-Flow Multiphase Pump Operating Air and Water Through Local Visualization and Analysis of Dynamic Measurements. ASME 2015 International Mechanical Engineering Congress & Exposition - Is not included due to copyright available at http://dx.doi.org/10.1115/IMECE2015-50398
Paper 3: Serena, Alberto; Bakken, Lars Eirik. Investigation of the Blade Tip Clearance Effects on Performance and Stability of a Mixed-Flow Pump: High Speed Camera Recordings of the Flow Structures, Local Measurements and Numerical Simulations. Internationational Mechanical Engineers Congress and Exposition - Is not included due to copyright available at http://dx.doi.org/10.1115/IMECE2015-50398
Paper 4: Serena, Alberto; Bakken, Lars Eirik. Experimental Study of the Influence of the Operating Parameters on the Performance and Capability of a Mixed-Flow Multiphase Pump. Proceedings of the ASME 2016 Turbomachinery Technical Conference and Exposition - Is not included due to copyright available at http://dx.doi.org/10.1115/GT2016-56576
Paper 5: Serena, Alberto; Bakken, Lars Eirik. Flow Visualization of Unsteady and Transient Phenomena in a Mixed-Flow Multiphase Pump. Proceedings of the ASME 2016 Turbomachinery Technical Conference and Exposition - Is not included due to copyright available at http://dx.doi.org/10.1115/GT2016-56581