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Yoshihide Kawashima - One of the best experts on this subject based on the ideXlab platform.
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Laboratory experiments for intense vortical structures in turbulence velocity fields
Physics of Fluids, 2007Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:Vortical structures of turbulence, i.e., vortex tubes and sheets, are studied using one-dimensional velocity data obtained in laboratory experiments for duct flows and boundary layers at microscale Reynolds numbers from 332 to 1934. We study the mean velocity profile of intense vortical structures. The contribution from vortex tubes is dominant. The radius scales with the Kolmogorov Length. The circulation velocity scales with the rms velocity fluctuation. We also study the spatial distribution of intense vortical structures. The distribution is self-similar over small scales and is random over large scales. Since these features are independent of the microscale Reynolds number and of the configuration for turbulence production, they appear to be universal.
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Vortex tubes in turbulence velocity fields at Reynolds numbers Re lambda approximately equal to 300-1300.
Physical review. E Statistical nonlinear and soft matter physics, 2004Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:The most elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in a laboratory experiment for boundary layers with Reynolds numbers Re(lambda) =295-1258 . We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov Length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. We also obtain the distribution of the interval between successive enhancements of the velocity increment as the measure of the spatial distribution of vortex tubes. They tend to cluster together below about the integral Length and more significantly below about the Taylor microscale. These properties are independent of the Reynolds number and are hence expected to be universal.
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Vortex tubes in turbulence velocity fields at Reynolds numbers Re λ ≃ 300 – 1300
Physical Review E, 2004Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:The most elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in a laboratory experiment for boundary layers with Reynolds numbers ${\mathrm{Re}}_{\ensuremath{\lambda}}=295--1258$. We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov Length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. We also obtain the distribution of the interval between successive enhancements of the velocity increment as the measure of the spatial distribution of vortex tubes. They tend to cluster together below about the integral Length and more significantly below about the Taylor microscale. These properties are independent of the Reynolds number and are hence expected to be universal.
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Vortex tubes in velocity fields of laboratory isotropic turbulence
Physics Letters A, 2000Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:Abstract The streamwise and transverse velocities are measured simultaneously in grid turbulence at Reynolds numbers 100–300. We extract typical intermittence patterns, which are consistent with velocity profiles of Burgers and Lamb–Oseen vortices. The radii of these vortex tubes are estimated to be several of the Kolmogorov Length.
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VORTEX TUBES IN VELOCITY FIELDS OF LABORATORY TURBULENCE AT HIGH REYNOLDS NUMBERS
Fluid Mechanics and Its Applications, 1Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:The most elementary structures of turbulence, i.e., vortex tubes, are studied using laboratory velocity data for boundary layers with Reynolds numbers Reλ = 295- 1258. We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov Length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. These properties are independent of the Reynolds number and are hence expected to be universal.
Marko Princevac - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic characterization within a spinner flask and a rotary wall vessel for stem cell culture
Biochemical Engineering Journal, 2020Co-Authors: Masoud Ghasemian, Ni ,zur Nieden, Carys Layton, Daniel Nampe, Hideaki Tsutsui, Marko PrincevacAbstract:Abstract Stirred suspension culture is becoming a popular method for expanding human pluripotent stem cells (hPSCs). While stirring generates adequate fluid motions to lift the cells and facilitates mass transfers (of nutrients, dissolved gases, and metabolic wastes), excessive stirring could impose hydrodynamic forces deleterious for the growth of the cells. In this study, computational fluid dynamics (CFD) simulations were performed to first investigate hydrodynamic characteristics of fluid flows in a spinner flask, a common stirred suspension culture vessel used in laboratories. Flow patterns and distributions of shear stresses and the Kolmogorov Length scales at varying impeller speeds were obtained. Comparison of the Kolmogorov Length scales and sizes of hPSC aggregates, measured in the authors’ previous experimental study, showed a strong correlation between the two. In addition to the spinner flask which generated complex and transient turbulent flows, this study investigated a newly developed rotary wall vessel that had been designed to produce laminar, circular Couette flows in order to control shear stress. CFD simulations revealed significantly more uniform and homogeneous flows compared to those in the spinner flask, suggesting that the rotary wall vessel is a suitable culture vessel to investigate roles of shear stress on hPSCs in suspension.
Hideaki Mouri - One of the best experts on this subject based on the ideXlab platform.
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Vortex Tubes in Turbulence Velocity Fields at High Reynolds Numbers
Fluid Dynamics Research, 2009Co-Authors: Hideaki Mouri, Akihiro HoriAbstract:The elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in laboratory experiments for boundary layers and duct flows at microscale Reynolds numbers 332-1934. While past experimental studies focused on intense vortex tubes, the present study focuses on all vortex tubes with various intensities. We obtain the mean velocity profile. The radius scales with the Kolmogorov Length. The circulation velocity scales with the Kolmogorov velocity, in contrast to the case of intense vortex tubes alone where the circulation velocity scales with the rms velocity fluctuation. Since these scaling laws are independent of the configuration for turbulence production, they appear to be universal at high Reynolds numbers.
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Laboratory experiments for intense vortical structures in turbulence velocity fields
Physics of Fluids, 2007Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:Vortical structures of turbulence, i.e., vortex tubes and sheets, are studied using one-dimensional velocity data obtained in laboratory experiments for duct flows and boundary layers at microscale Reynolds numbers from 332 to 1934. We study the mean velocity profile of intense vortical structures. The contribution from vortex tubes is dominant. The radius scales with the Kolmogorov Length. The circulation velocity scales with the rms velocity fluctuation. We also study the spatial distribution of intense vortical structures. The distribution is self-similar over small scales and is random over large scales. Since these features are independent of the microscale Reynolds number and of the configuration for turbulence production, they appear to be universal.
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Vortex tubes in turbulence velocity fields at Reynolds numbers Re lambda approximately equal to 300-1300.
Physical review. E Statistical nonlinear and soft matter physics, 2004Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:The most elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in a laboratory experiment for boundary layers with Reynolds numbers Re(lambda) =295-1258 . We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov Length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. We also obtain the distribution of the interval between successive enhancements of the velocity increment as the measure of the spatial distribution of vortex tubes. They tend to cluster together below about the integral Length and more significantly below about the Taylor microscale. These properties are independent of the Reynolds number and are hence expected to be universal.
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Vortex tubes in turbulence velocity fields at Reynolds numbers Re λ ≃ 300 – 1300
Physical Review E, 2004Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:The most elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in a laboratory experiment for boundary layers with Reynolds numbers ${\mathrm{Re}}_{\ensuremath{\lambda}}=295--1258$. We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov Length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. We also obtain the distribution of the interval between successive enhancements of the velocity increment as the measure of the spatial distribution of vortex tubes. They tend to cluster together below about the integral Length and more significantly below about the Taylor microscale. These properties are independent of the Reynolds number and are hence expected to be universal.
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Vortex tubes in velocity fields of laboratory isotropic turbulence
Physics Letters A, 2000Co-Authors: Hideaki Mouri, Akihiro Hori, Yoshihide KawashimaAbstract:Abstract The streamwise and transverse velocities are measured simultaneously in grid turbulence at Reynolds numbers 100–300. We extract typical intermittence patterns, which are consistent with velocity profiles of Burgers and Lamb–Oseen vortices. The radii of these vortex tubes are estimated to be several of the Kolmogorov Length.
Wolfgang Schröder - One of the best experts on this subject based on the ideXlab platform.
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Ambient Flow Properties of Kolmogorov-Length-Scale Size Non-Spherical Particles in Isotropic Turbulence
ERCOFTAC Series, 2020Co-Authors: Konstantin Fröhlich, Lennart Schneiders, Matthias Meinke, Wolfgang SchröderAbstract:A method to estimate the ambient flow encountered by ellipsoidal particles is assessed for 60,000 fully resolved Kolmogorov-Length-scale size ellipsoidal particles. A sensitivity analysis is presented to provide confidence intervals of the estimation method and averaged near-particle flow patterns yield further information on the disturbances of the particles. The estimation method is based on filtering and can accurately determine the ambient fluid velocity encountered by the particles. However, the ambient fluid rotation rate and the shear rate are partially filtered, which is related to the finite size of the particles.
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direct particle fluid simulation of Kolmogorov Length scale size particles in decaying isotropic turbulence
Journal of Fluid Mechanics, 2017Co-Authors: Lennart Schneiders, Matthias Meinke, Wolfgang SchröderAbstract:The modulation of decaying isotropic turbulence by 45 000 spherical particles of Kolmogorov-Length-scale size is studied using direct particle–fluid simulations, i.e. the flow field over each particle is fully resolved by direct numerical simulations of the conservation equations. A Cartesian cut-cell method is used by which the exchange of momentum and energy at the fluid–particle interfaces is strictly conserved. It is shown that the particles absorb energy from the large scales of the carrier flow while the small-scale turbulent motion is determined by the inertial particle dynamics. Whereas the viscous dissipation rate of the bulk flow is attenuated, the particles locally increase the level of dissipation due to the intense strain rate generated near the particle surfaces due to the crossing-trajectory effect. Analogously, the rotational motion of the particles decouples from the local fluid vorticity and strain-rate field at increasing particle inertia. The high level of dissipation is partially compensated by the transfer of momentum to the fluid via forces acting at the particle surfaces. The spectral analysis of the kinetic energy budget is supported by the average flow pattern about the particles showing a nearly universal strain-rate distribution. An analytical expression for the instantaneous rate of viscous dissipation induced by each particle is derived and subsequently verified numerically. Using this equation, the local balance of fluid kinetic energy around a particle of arbitrary shape can be precisely determined. It follows that two-way coupled point-particle models implicitly account for the particle-induced dissipation rate via the momentum-coupling terms; however, they disregard the actual Length scales of the interaction. Finally, an analysis of the small-scale flow topology shows that the strength of vortex stretching in the bulk flow is mitigated due to the presence of the particles. This effect is associated with the energy conversion at small wavenumbers and the reduced level of dissipation at intermediate wavenumbers. Consequently, it damps the spectral flux of energy to the small scales.
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Direct particle–fluid simulation of Kolmogorov-Length-scale size particles in decaying isotropic turbulence
Journal of Fluid Mechanics, 2017Co-Authors: Lennart Schneiders, Matthias Meinke, Wolfgang SchröderAbstract:The modulation of decaying isotropic turbulence by 45 000 spherical particles of Kolmogorov-Length-scale size is studied using direct particle–fluid simulations, i.e. the flow field over each particle is fully resolved by direct numerical simulations of the conservation equations. A Cartesian cut-cell method is used by which the exchange of momentum and energy at the fluid–particle interfaces is strictly conserved. It is shown that the particles absorb energy from the large scales of the carrier flow while the small-scale turbulent motion is determined by the inertial particle dynamics. Whereas the viscous dissipation rate of the bulk flow is attenuated, the particles locally increase the level of dissipation due to the intense strain rate generated near the particle surfaces due to the crossing-trajectory effect. Analogously, the rotational motion of the particles decouples from the local fluid vorticity and strain-rate field at increasing particle inertia. The high level of dissipation is partially compensated by the transfer of momentum to the fluid via forces acting at the particle surfaces. The spectral analysis of the kinetic energy budget is supported by the average flow pattern about the particles showing a nearly universal strain-rate distribution. An analytical expression for the instantaneous rate of viscous dissipation induced by each particle is derived and subsequently verified numerically. Using this equation, the local balance of fluid kinetic energy around a particle of arbitrary shape can be precisely determined. It follows that two-way coupled point-particle models implicitly account for the particle-induced dissipation rate via the momentum-coupling terms; however, they disregard the actual Length scales of the interaction. Finally, an analysis of the small-scale flow topology shows that the strength of vortex stretching in the bulk flow is mitigated due to the presence of the particles. This effect is associated with the energy conversion at small wavenumbers and the reduced level of dissipation at intermediate wavenumbers. Consequently, it damps the spectral flux of energy to the small scales.
Christos J Vassilicos - One of the best experts on this subject based on the ideXlab platform.
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nonequilibrium scaling of the turbulent nonturbulent interface speed in planar jets
Physical Review Letters, 2020Co-Authors: Gioacchino Cafiero, Christos J VassilicosAbstract:The Length scale which, combined with the fluid's kinematic viscosity $\ensuremath{\nu}$, defines the local average speed of the turbulent-nonturbulent interface has been postulated to be the smallest (Kolmogorov) Length scale $\ensuremath{\eta}$ of the turbulence Corrsin and Kistler, [NACA Report No. 1244, 1955, p. 1033.]. This is indeed the case when the turbulence dissipation rate obeys the Kolmogorov equilibrium cascade scaling, but in the presence of the nonequilibrium turbulence dissipation scaling the average local turbulent-nonturbulent interface speed scales as $\ensuremath{\nu}/\ensuremath{\lambda}$, instead of $\ensuremath{\nu}/\ensuremath{\eta}$, where $\ensuremath{\lambda}$ is the Taylor Length. We derive this theoretically and confirm it experimentally in the range of distances between 20 and 50 nozzle widths of a turbulent planar jet.
