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Experimental study of velocity statistics in wall-bounded turbulent emulsions

Published online by Cambridge University Press:  13 May 2025

Yaning Fan Open the ORCID record for Yaning Fan [Opens in a new window] ,
Yi-Bao Zhang Open the ORCID record for Yi-Bao Zhang [Opens in a new window] ,
Jinghong Su Open the ORCID record for Jinghong Su [Opens in a new window] ,
Lei Yi Open the ORCID record for Lei Yi [Opens in a new window] ,
Cheng Wang Open the ORCID record for Cheng Wang [Opens in a new window]  and
Chao Sun Open the ORCID record for Chao Sun [Opens in a new window]
Yaning Fan
Affiliation:
New Cornerstone Science Laboratory, Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, PR China
Yi-Bao Zhang
Affiliation:
New Cornerstone Science Laboratory, Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, PR China
Jinghong Su
Affiliation:
New Cornerstone Science Laboratory, Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, PR China
Lei Yi
Affiliation:
New Cornerstone Science Laboratory, Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, PR China Department of Physics, University of Massachusetts, Amherst, MA 01003, USA
Cheng Wang
Affiliation:
New Cornerstone Science Laboratory, Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, PR China ENS de Lyon, CNRS, Laboratoire de physique, Lyon F-69342, France
Chao Sun*
Affiliation:
New Cornerstone Science Laboratory, Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, PR China Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, PR China
*
Correspondence author: Chao Sun, chaosun@tsinghua.edu.cn
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Abstract

Turbulent emulsions are ubiquitous in chemical engineering, food processing, pharmaceuticals and other fields. However, our experimental understanding of this area remains limited due to the multiscale nature of turbulent flow and the presence of extensive interfaces, which pose significant challenges to optical measurements. In this study, we address these challenges by precisely matching the refractive indices of the continuous and dispersed phases, enabling us to measure local velocity information at high volume fractions. The emulsion is generated in a turbulent Taylor–Couette flow, with velocity measured at two radial locations: near the inner cylinder (boundary layer) and in the middle gap (bulk region). Near the inner cylinder, the presence of droplets suppresses the emission of angular velocity plumes, which reduces the mean azimuthal velocity and its root mean squared fluctuation. The former effect leads to a higher angular velocity gradient in the boundary layer, resulting in greater global drag on the system. In the bulk region, although droplets suppress turbulence fluctuations, they enhance the cross-correlation between azimuthal and radial velocities, leaving the angular velocity flux contributed by the turbulent flow nearly unchanged. In both locations, droplets suppress turbulence at scales larger than the average droplet diameter and increase the intermittency of velocity increments. However, the effects of the droplets are more pronounced near the inner cylinder than in the bulk, likely because droplets fragment in the boundary layer but are less prone to break up in the bulk. Our study provides experimental insights into how dispersed droplets modulate global drag, coherent structures and the multiscale characteristics of turbulent flow.

JFM classification

Complex Fluids: Emulsions Instability: Taylor-Couette flow Multiphase and Particle-laden Flows: Multiphase flow

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Type
JFM Papers
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Journal of Fluid Mechanics , Volume 1011 , 25 May 2025 , A14
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© The Author(s), 2025. Published by Cambridge University Press

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Footnotes

†

Yaning Fan, Yi-Bao Zhang contributed equally to this work.

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