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Characterization of turbulent flows of non-Newtonian fluids using magnetic resonance velocimetry
KTH, School of Engineering Sciences (SCI), Engineering Mechanics.ORCID iD: 0000-0002-7275-8756
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Sustainable development
SDG 16: Peace, justice and strong institutions, SDG 6: Clean water and sanitation, SDG 3: Good Health and Well-Being
Abstract [en]

Fluids consisting of dispersed spherical and non-spherical particles are commonly found in many natural and industrial processes. The intricate interplay between particle-particle and particle-fluid interactions, along with flow dynamics and geometries, leads to complex flow phenomena, which still needs to be better understood. Accurate modelling of such flows are crucial for predicting and optimizing processes occurring in, for example, paper industry and wastewater treatment. Both experimental and numerical approaches have been utilized to obtain the flow information, each offering distinct insights. However, a major challenge lies in developing and validating numerical models due to limited or non-existent experimental data. Capturing and measuring these complex flows experimentally is difficult, due to limited optical access, high solid concentrations and often, the measurement probes can affect the flow. On the other hand, numerical simulations can capture these intricate interactions, however, they rely on assumptions and are constrained by high computational expenses.

For high solid concentrations of particles, magnetic resonance velocimetry (MRV) has emerged as a successful non-invasive experimental technique capable of capturing the flow phenomena. Nonetheless, the existing MRV protocols contains questionable assumptions and is dependent on specific parameters for measurements. This thesis addresses these challenges by investigating and characterizing turbulent flows of non-Newtonian fluids through combined MRV measurements and computational fluid dynamics (CFD) simulations. The work also demonstrates how robust quantitative comparisons between MRV measurements and CFD simulations can be achieved, paving the way for development of accurate, calibrated flow models and highlighting the need for size-dependent rheological models in particle-laden turbulent pipe flows. 

The findings of this work contribute to a deeper understanding of complex flows, offering a pathway for improved predictive models that can be applied in various industrial and environmental contexts. The research also highlights the potential of MRV to overcome traditional experimental limitations and underscores the importance of integrating experiments and numerical simulations to advance the study of non-Newtonian and complex fluid flows.

Abstract [sv]

Fluider beståendes av sfäriska och icke-sfäriska partiklar förekommer ofta i många naturliga och industriella processer. Det intrikata samspelet mellan partikel-partikel- och partikel-fluidinteraktioner, tillsammans med strömnings-dynamik och geometriska variationer, leder till komplexa flödesfenomen som fortfarande behöver förstås bättre. Noggrann modellering av sådana flöden är avgörande för att kunna förutsäga och optimera processer exempelvis inom pappersindustrin och rening av avloppsvatten. Både experimentella och numeriska tillvägagångssätt har använts för att få fram information om flödet, där varje metod ger unika insikter. Dock finns en stor utmaning i att utveckla och validera numeriska modeller på grund av begränsade eller obefintliga experimentella data. Att fånga och mäta dessa komplexa flöden experimentellt är svårt på grund av begränsad optisk tillgång, höga partikelfraktioner och möjlig påverkan från mätproberna på flödet. Å andra sidan kan numeriska simuleringar fånga dessa intrikata interaktioner, men de är beroende av antaganden och begränsas av höga beräkningskostnader.

För höga partikelfraktioner har magnetresonansvelocimetri (MRV) blivit en framgångsrik icke-invasiv experimentell teknik som kan fånga dessa flödesfenomen. Trots detta innehåller de nuvarande MRV-protokollen antaganden som kan ifrågasättas och är dessutom beroende av specifika parametrar för mätningarna. Denna avhandling tar itu med dessa utmaningar genom att undersöka och karakterisera turbulenta flöden av icke-Newtonska vätskor genom kombinerade MRV-mätningar och numeriska simuleringar av flödesdynamik (CFD). Arbetet visar även hur robusta kvantitativa jämförelser mellan MRV-mätningar och CFD-simuleringar kan uppnås, vilket banar väg för utveckling av exakta och kalibrerade flödesmodeller samt betonar behovet av storleksberoende reologiska modeller i partikelbelastade turbulenta rörflöden.

Resultaten av detta arbete bidrar till en djupare förståelse för komplexa flöden och erbjuder en väg mot förbättrade prediktiva modeller som kan tillämpas i olika industriella och miljömässiga sammanhang. Forskningen lyfter också fram potentialen hos MRV för att övervinna traditionella experimentella begränsningar och understryker vikten av att integrera experiment och numeriska simuleringar för att främja studiet av icke-Newtonska och komplexa vätskeflöden.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024.
Series
TRITA-SCI-FOU ; 2024:39
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-355073ISBN: 978-91-8106-088-1 (print)OAI: oai:DiVA.org:kth-355073DiVA, id: diva2:1907001
Public defence
2024-11-11, Kollegiesalen (Nr 4301), Brinellvägen 8, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 241021

Available from: 2024-10-21 Created: 2024-10-21 Last updated: 2024-10-28Bibliographically approved
List of papers
1. Pipe flow with large particles and their impact on the transition to turbulence
Open this publication in new window or tab >>Pipe flow with large particles and their impact on the transition to turbulence
2020 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, no 11, article id 112301Article in journal (Refereed) Published
Abstract [en]

The classical transition from laminar to turbulent flow is affected if solid particles are added. The transition behavior is a function of particle size d and solid volume fraction phi and the flow undergoes a smooth transition, as opposed to intermittent, if phi exceeds a certain threshold. In this work we show that, for particle-laden pipe flows with large particle-to-pipe diameter ratios d/D, the phi threshold for altering the transition is much lower than previously reported for smaller particles. Magnetic resonance velocimetry reveals that particles introduce turbulent-like fluid velocity fluctuations in laminar flow. Factors that might control the limits between "classical" and "smooth" transition in the state space spanned by d/D and phi are discussed based on scaling analyses.

Place, publisher, year, edition, pages
American Physical Society (APS), 2020
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-287504 (URN)10.1103/PhysRevFluids.5.112301 (DOI)000589611200001 ()2-s2.0-85097573147 (Scopus ID)
Note

QC 20210303

Available from: 2021-03-03 Created: 2021-03-03 Last updated: 2024-10-21Bibliographically approved
2. Turbulent pipe flow with spherical particles: Drag as a function of particle size and volume fraction
Open this publication in new window or tab >>Turbulent pipe flow with spherical particles: Drag as a function of particle size and volume fraction
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2024 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 179, article id 104931Article in journal (Refereed) Published
Abstract [en]

Suspensions of finite-size solid particles in a turbulent pipe flow are found in many industrial and technical flows. Due to the ample parameter space consisting of particle size, concentration, density and Reynolds number, a complete picture of the particle-fluid interaction is still lacking. Pressure drop predictions are often made using viscosity models only considering the bulk solid volume fraction. For the case of turbulent pipe flow laden with neutrally buoyant spherical particles, we investigate the pressure drop and overall drag (friction factor), fluid velocity and particle distribution in the pipe. We use a combination of experimental (MRV) and numerical (DNS) techniques and a continuum flow model. We find that the particle size and the bulk flow rate influence the mean fluid velocity, velocity fluctuations and the particle distribution in the pipe for low flow rates. However, the effects of the added solid particles diminish as the flow rate increases. We created a master curve for drag change compared to single-phase flow for the particle-laden cases. This curve can be used to achieve more accurate friction factor predictions than the traditional modified viscosity approach that does not account for particle size.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Particle suspensions, Turbulent pipe flow, Pressure loss prediction, Spherical particles
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-352541 (URN)10.1016/j.ijmultiphaseflow.2024.104931 (DOI)001288603600001 ()2-s2.0-85200113925 (Scopus ID)
Note

QC 20240903

Available from: 2024-09-03 Created: 2024-09-03 Last updated: 2024-10-21Bibliographically approved
3. MRV Measurements of Fiber Suspension Flow Through an Axisymmetric Constriction
Open this publication in new window or tab >>MRV Measurements of Fiber Suspension Flow Through an Axisymmetric Constriction
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Measurements of turbulent flow of two types of fibre suspensions in the semi-dilute regime are performed. The flow investigated in this work displays an intriguing combination of complexities stemming from the flow geometry, the rheology of the suspension and the turbulence of the flow. Although the suspensions have similar concentrations and the two types of fibres geometrically resemble each other, the MRV measurements reveal an asymmetric behavior in the flow field of the flexible cellulose fibres.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-355070 (URN)
Note

QC 20241028

Available from: 2024-10-21 Created: 2024-10-21 Last updated: 2024-10-28Bibliographically approved
4. Robust reproduction of PC-MRI data from DNS
Open this publication in new window or tab >>Robust reproduction of PC-MRI data from DNS
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Acquiring velocity statistics using PC-MRIhas been a standard procedure for some time. Mean velocities are often accurately measured, but velocity fluctuation comparisons are less precise. The standard turbulent protocol used, relies on an assumption of the velocity distribution that does not hold for all flows, for instance close to solid walls. In this work we investigate the possibilities to reverse the process, reproduce the PC-MRI signal from known velocity distributions using high-fidelity simulations of two canonical flows, open-channel and pipe flow. Results show that a naive approach, using converged velocity distributions leads to discrepancies, but close agreement to experimentally estimated velocity fluctuations is reached when a multiple realisation method is used. This work showcases the potential of simulating MR signals from DNS data in order to calibrate and improve flow models of complex flow environments.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-355071 (URN)
Note

QC 20241028

Available from: 2024-10-21 Created: 2024-10-21 Last updated: 2024-10-28Bibliographically approved

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Leskovec, Martin

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