LDV measurements and numerical modeling of the turbulent flow in a stirred mixer.

Persistent Link:
http://hdl.handle.net/10150/184528
Title:
LDV measurements and numerical modeling of the turbulent flow in a stirred mixer.
Author:
Wu, Howard Honezern.
Issue Date:
1988
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
It is recognized that detailed knowledge of turbulence parameters, as well as velocities, can aid in understanding and modeling mixing rate-dominated phenomena in stirred vessels. Measurements using a laser-Doppler velocimeter and modeling using a k-ε turbulence model and FLUENT, a general-purpose fluid flow modeling program, have been conducted of the flow in a baffled, turbine-agitated vessel. The complex flow patterns and high turbulence intensities explain why flows in stirred vessels are difficult to attack experimentally or numerically. In the measurements, the necessary corrections for the periodic, nondissipative velocity fluctuations in the near-impeller region, which were caused by the periodic passage of the impeller blades, were made by an autocorrelation method. With the contributions of the periodic fluctuations removed, meaningful turbulence data including turbulence intensities, autocorrelation functions, turbulence energy spectra, turbulence scales, and turbulence energy dissipation rates were obtained. Integral scales and energy dissipation rates were a particular objective in this work because of their usefulness in modeling local mixing rates in turbulent flows. An energy balance around a region containing the impeller and the impeller stream showed that 60% of the energy transmitted into the vessel via the impeller was dissipated in the region, and 40% was dissipated in the rest of the vessel. An equation for calculating local energy dissipation rates ε from total turbulence energy and resultant integral scales, ε = A q³/² /L(res), appeared adequate with constant A = 0.85 (where q ≡ uᵢuᵢ/2, L(res) ≡√LᵢLᵢ, and uᵢ and Lᵢ are, respectively, the i-th component of fluctuation velocity and the turbulence integral scale measured in direction i). Both the k-ε model (two-dimensional) and FLUENT (which employed three-dimensional k-ε and Reynolds stress models) obtained mean velocity profiles fairly close to the experimental data, but both predicted k and ε significantly lower than the measured values. The reason for the underestimation of k and ε was not entirely clear, but may have been caused by use of only the random parts of velocities for computing k and ε at the impeller boundary. The objective of modeling complex turbulent flows in stirred vessels has been accomplished, a goal which until recently would have been considered beyond the possibility of computation.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Turbulence -- Computer simulation.; Mixing machinery.; Laser Doppler velocimeter.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemical Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Patterson, Gary K.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleLDV measurements and numerical modeling of the turbulent flow in a stirred mixer.en_US
dc.creatorWu, Howard Honezern.en_US
dc.contributor.authorWu, Howard Honezern.en_US
dc.date.issued1988en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractIt is recognized that detailed knowledge of turbulence parameters, as well as velocities, can aid in understanding and modeling mixing rate-dominated phenomena in stirred vessels. Measurements using a laser-Doppler velocimeter and modeling using a k-ε turbulence model and FLUENT, a general-purpose fluid flow modeling program, have been conducted of the flow in a baffled, turbine-agitated vessel. The complex flow patterns and high turbulence intensities explain why flows in stirred vessels are difficult to attack experimentally or numerically. In the measurements, the necessary corrections for the periodic, nondissipative velocity fluctuations in the near-impeller region, which were caused by the periodic passage of the impeller blades, were made by an autocorrelation method. With the contributions of the periodic fluctuations removed, meaningful turbulence data including turbulence intensities, autocorrelation functions, turbulence energy spectra, turbulence scales, and turbulence energy dissipation rates were obtained. Integral scales and energy dissipation rates were a particular objective in this work because of their usefulness in modeling local mixing rates in turbulent flows. An energy balance around a region containing the impeller and the impeller stream showed that 60% of the energy transmitted into the vessel via the impeller was dissipated in the region, and 40% was dissipated in the rest of the vessel. An equation for calculating local energy dissipation rates ε from total turbulence energy and resultant integral scales, ε = A q³/² /L(res), appeared adequate with constant A = 0.85 (where q ≡ uᵢuᵢ/2, L(res) ≡√LᵢLᵢ, and uᵢ and Lᵢ are, respectively, the i-th component of fluctuation velocity and the turbulence integral scale measured in direction i). Both the k-ε model (two-dimensional) and FLUENT (which employed three-dimensional k-ε and Reynolds stress models) obtained mean velocity profiles fairly close to the experimental data, but both predicted k and ε significantly lower than the measured values. The reason for the underestimation of k and ε was not entirely clear, but may have been caused by use of only the random parts of velocities for computing k and ε at the impeller boundary. The objective of modeling complex turbulent flows in stirred vessels has been accomplished, a goal which until recently would have been considered beyond the possibility of computation.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectTurbulence -- Computer simulation.en_US
dc.subjectMixing machinery.en_US
dc.subjectLaser Doppler velocimeter.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemical Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorPatterson, Gary K.en_US
dc.contributor.committeememberWendt, Jost O. L.en_US
dc.contributor.committeememberPeterson, Thomas W.en_US
dc.contributor.committeememberPearlstein, Arne J.en_US
dc.contributor.committeememberRamohalli, Kumar N. R.en_US
dc.identifier.proquest8902363en_US
dc.identifier.oclc701548010en_US
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