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A Multiphase Pump Experimental Analysis

Serena, Alberto
Doctoral thesis
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2016-215_Alberto_Serena_PhD.pdf (Locked)
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URI
http://hdl.handle.net/11250/2410476
Date
2016
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  • Institutt for energi og prosessteknikk [4019]
Abstract
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.
Has parts
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/POWER2015-49769

Paper 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
Publisher
NTNU
Series
Doctoral thesis at NTNU;2016:215

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