Victor Steinberg - Profile on Academia.edu (original) (raw)

Papers by Victor Steinberg

Nature, May 1, 2000

Turbulence is one of the most fascinating phenomena in nature and one of the biggest challenges f... more Turbulence is one of the most fascinating phenomena in nature and one of the biggest challenges for modern physics. It is common knowledge that a flow of a simple, Newtonian fluid is likely to be turbulent, when velocity is high, viscosity is low and size of the tank is large [1,2]. Solutions of flexible longchain polymers are known as visco-elastic fluids [3]. In our experiments we show, that flow of a polymer solution with large enough elasticity can become quite irregular even at low velocity, high viscosity and in a small tank. The fluid motion is excited in a broad range of spatial and temporal scales. The flow resistance increases by a factor of about twenty. So, while the Reynolds number, Re, may be arbitrary low, the observed flow has all main features of developed turbulence, and can be compared to turbulent flow in a pipe at Re ≃ 10 5 [1,2].

EPL, Jul 1, 2014

We present experimental observations and numerical simulations of a wrinkling instability that oc... more We present experimental observations and numerical simulations of a wrinkling instability that occurs at sufficiently high strain rates in the trembling regime of vesicle dynamics in steady linear flow. Spectral and statistical analysis of the data shows similarities and differences with the wrinkling instability observed earlier for vesicles in transient elongation flow. The critical relevance of thermal fluctuations for this phenomenon is revealed by a simple model using coupled Langevin equations that reproduces the experimental observations quite well.

arXiv (Cornell University), Dec 2, 2021

Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent str... more Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent stretching can result in the coil-stretch transition. This phenomenon has been characterized by using the formalism of nonequilibrium statistical mechanics. In particular, the entropy of the polymer extension reaches a maximum at the transition. We extend the entropic characterization of the coil-stretch transition by studying the differential entropy of the polymer fractional extension in a set of laminar and random velocity fields that are benchmarks for the study of polymer stretching in flow. In the case of random velocity fields, a suitable description of the transition is obtained by considering the entropy of the logarithm of the extension instead of the entropy of the extension itself. Entropy emerges as an effective tool for capturing the coil-stretch transition and comparing its features in different flows.

Physical Review E, May 18, 2012

We report the experimental studies on interaction of two vesicles trapped in a micro-fluidic four... more We report the experimental studies on interaction of two vesicles trapped in a micro-fluidic fourroll mill, where a plane linear flow is realized. We found that the dynamics of a vesicle in tanktreading motion is significantly altered by the presence of another vesicle at separation distances up to 3.2 ÷ 3.7 times of the vesicle effective radius. This result is supported by measurement of a single vesicle back-reaction on the velocity field. Thus, the experiment provides the upper bound for the volume fraction φ = 0.08 ÷ 0.13 of non-interacting vesicle suspensions.

Advances in Colloid and Interface Science, Jun 1, 2014

We review the dynamical behavior of giant fluid vesicles in various types of external hydrodynami... more We review the dynamical behavior of giant fluid vesicles in various types of external hydrodynamic flow. The interplay between stresses arising from membrane elasticity, hydrodynamic flows, and the ever present thermal fluctuations leads to a rich phenomenology. In linear flows with both rotational and elongational components, the properties of the tank-treading and tumbling motions are now well described by theoretical and numerical models. At the transition between these two regimes, strong shape deformations and amplification of thermal fluctuations generate a new regime called trembling. In this regime, the vesicle orientation oscillates quasi-periodically around the flow direction while asymmetric deformations occur. For strong enough flows, small-wavelength deformations like wrinkles are observed, similar to what happens in a suddenly reversed elongational flow. In steady elongational flow, vesicles with large excess areas deform into dumbbells at large flow rates and pearling occurs for even stronger flows. In capillary flows with parabolic flow profile, single vesicles migrate towards the center of the channel, where they adopt symmetric shapes, for two reasons. First, walls exert a hydrodynamic lift force which pushes them away. Second, shear stresses are minimal at the tip of the flow. However, symmetry is broken for vesicles with large excess areas, which flow off-center and deform asymmetrically. In suspensions, hydrodynamic interactions between vesicles add up to these two effects, making it challenging to deduce rheological properties from the dynamics of individual vesicles. Further investigations of vesicles and similar objects and their suspensions in steady or time-dependent flow will shed light on phenomena such as blood flow.

Nature Communications, Feb 26, 2019

Electron transport in two-dimensional conducting materials such as graphene, with dominant electr... more Electron transport in two-dimensional conducting materials such as graphene, with dominant electron-electron interaction, exhibits unusual vortex flow that leads to a nonlocal currentfield relation (negative resistance), distinct from the classical Ohm's law. The transport behavior of these materials is best described by low Reynolds number hydrodynamics, where the constitutive pressure-speed relation is Stoke's law. Here we report evidence of such vortices observed in a viscous flow of Newtonian fluid in a microfluidic device consisting of a rectangular cavity-analogous to the electronic system. We extend our experimental observations to elliptic cavities of different eccentricities, and validate them by numerically solving bi-harmonic equation obtained for the viscous flow with no-slip boundary conditions. We verify the existence of a predicted threshold at which vortices appear. Strikingly, we find that a two-dimensional theoretical model captures the essential features of three-dimensional Stokes flow in experiments.

Journal of Fluid Mechanics, May 5, 2022

We examine the response of an inertialess viscoelastic channel flow to localized perturbations. W... more We examine the response of an inertialess viscoelastic channel flow to localized perturbations. We thus performed an experiment in which we perturbed the flow using a localized velocity pulse and probed the perturbed fluid packet downstream from the perturbation location. While for low Weissenberg numbers the perturbed fluid reaches the measurement location as a single velocity pulse, for sufficiently high Weissenberg numbers and perturbation strengths, a random number of pulses arrive at the measurement location. The average number of pulses observed increases with the Weissenberg number. This observation constitutes a transition to a novel elastic pulse-splitting regime. Our results suggest a possible new direction for studying the elastic instability of viscoelastic channel flows at high elasticity through the growth of localized perturbations.

Rotating Rayleigh-Bénard convection: Küppers-Lortz transition

Physica D: Nonlinear Phenomena, Aug 1, 1991

Abstract Rayleigh-Bénard convection with rotation about a vertical axis is investigated for small... more Abstract Rayleigh-Bénard convection with rotation about a vertical axis is investigated for small dimensionless rotation rates 0< Ω< 50. The convection cell is cylindrical with aspect ratio Γ= 10 and the convecting fluid is water with a Prandtl number of 6.8 at T= 23.8 C. ...

Physical review fluids, Oct 15, 2018

Creeping flow of polymeric fluid without inertia exhibits elastic instabilities and elastic turbu... more Creeping flow of polymeric fluid without inertia exhibits elastic instabilities and elastic turbulence accompanied by drag enhancement due to elastic stress produced by flow-stretched polymers. However, in inertia-dominated flow at high Re and low fluid elasticity El, a reduction in turbulent frictional drag is caused by an intricate competition between inertial and elastic stresses. Here, we explore the effect of inertia on the stability of viscoelastic flow in a broad range of control parameters El and (Re, Wi). We present the stability diagram of observed flow regimes in Wi -Re coordinates and find that instabilities' onsets show unexpectedly non-monotonic dependence on El. Further, three distinct regions in the diagram are identified based on El. Strikingly, for high elasticity fluids we discover a complete relaminarization of flow at Reynolds number of the order of unity, different from a well-known turbulent drag reduction. These counterintuitive effects may be explained by a finite polymer extensibility and a suppression of vorticity at high Wi. Our results call for further theoretical and numerical development to uncover the role of inertial effect on elastic turbulence in a viscoelastic flow.

Physical review fluids, Oct 16, 2018

We report quantitative evidence of mixing-layer elastic instability in a viscoelastic fluid flow ... more We report quantitative evidence of mixing-layer elastic instability in a viscoelastic fluid flow between two widely spaced obstacles hindering a channel flow at Re 1 and W i 1. Two mixing layers with nonuniform shear velocity profiles are formed in the region between the obstacles. The mixing-layer instability arises in the vicinity of an inflection point on the shear velocity profile with a steep variation in the elastic stress. The instability results in an intermittent appearance of small vortices in the mixing layers and an amplification of spatio-temporal averaged vorticity in the elastic turbulence regime. The latter is characterized through scaling of friction factor with W i, and both pressure and velocity spectra. Furthermore, the observations reported provide improved understanding of the stability of the mixing layer in a viscoelastic fluid at large elasticity, i.e. W i 1 and Re 1, and oppose the current view of suppression of vorticity solely by polymer additives.

Physical Review E, Nov 29, 2012

Physics of Fluids, Apr 1, 2012

The influence of symmetrical non-Oberbeck-Boussinesq (SNOB) effect on statistical and scaling pro... more The influence of symmetrical non-Oberbeck-Boussinesq (SNOB) effect on statistical and scaling properties of temperature field in turbulent convection is investigated experimentally in SF 6 in the vicinity of its gas-liquid critical point (CP). The main conclusion of the studies is that besides the strong Ra and P r dependence of the rms of temperature fluctuations normalized by the temperature difference across the cell, different from the Oberbeck-Boussinesq (OB) case of turbulent convection, all rest of statistical and scaling properties of temperature field discussed in details are the same as in the OB case.

Physical review fluids, Jun 15, 2022

In this paper, we present experimental results and reveal that strong perturbations are not neces... more In this paper, we present experimental results and reveal that strong perturbations are not necessary for elastic instability to occur in straight-channel, inertialess, viscoelastic flows at high elasticity. We show that a non-normal-mode bifurcation is followed by chaotic fluctuations, self-organized as streamwise streaks, and elastic waves due to weak disturbances generated by a small cavity at the center of the top channel wall. The chaotic flow persists in the transition, elastic turbulence, and drag reduction regimes, in agreement with previous observations for the case of strong perturbations at the inlet. Furthermore, the observed elastic waves propagate in the spanwise direction, which allows us to confirm the elastic waves' linear dispersion relation directly. In addition, the spanwise propagating elastic wave's velocity depends on Weissenberg number with the same scaling that was previously observed for streamwise propagating waves, although their velocity magnitude is significantly smaller than what was previously observed for the streamwise ones.

Physical Review E, Nov 28, 2011

We report detailed quantitative studies of elastic turbulence in a curvilinear channel flow in a ... more We report detailed quantitative studies of elastic turbulence in a curvilinear channel flow in a dilute polymer solution of high molecular weight polyacrylamide in a high viscosity water-sugar solvent. Detailed studies of the average and rms velocity and velocity gradients profiles reveal an emergence of the boundary layer associated with the nonuniform distribution of the elastic stresses across the channel. The characteristic boundary width is independent of the Weissenberg number W i and proportional to the channel width that follows from our early investigations of the boundary layer in elastic turbulence of different flow geometries. The appearance of the characteristic spatial scales of the order of the boundary layer width of both velocity and velocity gradient in the correlation functions of the velocity and velocity gradient fields in a bulk flow suggests that rare and strong parcels of excessive elastic stresses, concentrated in the boundary layer, are ejected into the bulk flow similar to jets observed in passive scalar mixing. And finally, the experimental results show that one of the main predictions of the theory of elastic turbulence, namely the saturation of the normalized rms velocity gradient in the bulk flow of elastic turbulence contradicts to the experimental observations both qualitatively and quantitatively in spite of the fact that the theory explains well the observed sharp decay of the velocity power spectrum. The experimental findings call for further development of theory of elastic turbulence in a bounded container, similar to what was done for a passive scalar problem.

Physical review fluids, May 17, 2023

Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent str... more Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent stretching can result in the coil-stretch transition. The statistics of polymer deformation depends strongly on the nature and the properties of the flow. Sultanov et al. [Phys. Rev. E 103, 033107 (2021)] have characterized the coil-stretch transition in an elastic turbulence of von Kármán flow by measuring the entropy of polymer extension as a function of the Weissenberg number. The entropic characterization of the coil-stretch transition is here extended to a set of laminar and random velocity fields that are benchmarks for the study of polymer stretching in flow. In the case of random velocity fields, a suitable description of the transition is obtained by considering the entropy of the logarithm of the extension instead of the entropy of the extension itself. Entropy emerges as an effective tool for capturing the coil-stretch transition and comparing its features in different flows.

Bulletin of the American Physical Society, Nov 20, 2006

Fluid vesicle dynamics and interaction in shear flow. VASILIY KANTSLER, ENRICO SERGE, VICTOR STEI... more Fluid vesicle dynamics and interaction in shear flow. VASILIY KANTSLER, ENRICO SERGE, VICTOR STEINBERG, DEPARTENT OF PHYSICS OF COMPLEX SYSTEMS TEAM -We present experimental results on single vesicle behavior subjected to shear flow, as well as the hydrodynamic interaction between neighboring vesicles. Moreover the dynamics of a vesicle in many-vesicle field is also studied. Tank treading, trembling and tumbling regimes of the motion are described in terms of the dimensionless variables, such as viscosity contrast, excess area and the dimensionless shear. It should be emphasized that vesicle interaction considerably increases tank treading angle fluctuations, though suppressing the transition to tumbling motion.

Bulletin of the American Physical Society, Mar 10, 2008

The properties of elastic turbulence in semi-dilute polymer solutions YONGGUN JUN, Physics of Com... more The properties of elastic turbulence in semi-dilute polymer solutions YONGGUN JUN, Physics of Complex Systems, Weizmann Institute of Science, VICTOR STEINBERG -We studied elastic turbulence in Karman swirling flow of semi-dilute polymer solution. The concentrations of polymer solution used in the experiment were 100, 300, 500, 700, and 900 ppm, and the velocity fields to calculate the rms of the gradients of the tangential velocity, ω rms , were obtained using PIV. First we checked the saturation of ω rms in the bulk, which represents the saturation of elastic stress. We found that W i bulk = ω rms τ saturates and approaches to unitary value as the polymer concentration increases. Here τ is the longest polymer relaxation time. Also we studied existence of the velocity boundary layer which is related to boundary layer of elastic stresses of elastic turbulence. The thickness of the boundary layer is the decreasing function of polymer concentration near the rotating upper plate but independent of concentrations near the wall.

arXiv (Cornell University), Sep 25, 2020

In the present study, we investigated flow structures and properties of elastic turbulence in str... more In the present study, we investigated flow structures and properties of elastic turbulence in straight 2D channel viscoelastic fluid flow and tested earlier observations. We discovered self-organized cycling process of weakly unstable coherent structures (CSs) of co-existing streaks and stream-wise vortices, with the former being destroyed by Kelvin-Helmholtz-like instability resulting in chaotic structures. The sequence periodically repeats itself leading to stochastically steady state. This selfsustained process (SSP) remarkably resembles one investigated theoretically and experimentally for Newtonian turbulence in straight channel flow. The unexpected new ingredient is the observation of elastic waves, which finds to be critical for existence of CSs and SSP generation due to energy pumping from large to smaller scales preceding sharp power-law decay in elastic turbulence energy spectrum. The reported finding suggests the universality of CSs in transition to turbulence via self-organized cycling (SSP) in linearly stable plane shear flows of both elastic and Newtonian fluids.

Physical Review Letters, May 16, 1988

A maior purpose of the Technical Information Center is to provide the broadest dissemination poss... more A maior purpose of the Technical Information Center is to provide the broadest dissemination possible of information contained in DOE's Research and Development Reports to business, industry, the academic community, and federal, state and local governments. Although a small portion of this report is not reproducible, it is being made available to expedite the availability of information on the research discussed herein.

Nature, May 1, 2000

Turbulence is one of the most fascinating phenomena in nature and one of the biggest challenges f... more Turbulence is one of the most fascinating phenomena in nature and one of the biggest challenges for modern physics. It is common knowledge that a flow of a simple, Newtonian fluid is likely to be turbulent, when velocity is high, viscosity is low and size of the tank is large [1,2]. Solutions of flexible longchain polymers are known as visco-elastic fluids [3]. In our experiments we show, that flow of a polymer solution with large enough elasticity can become quite irregular even at low velocity, high viscosity and in a small tank. The fluid motion is excited in a broad range of spatial and temporal scales. The flow resistance increases by a factor of about twenty. So, while the Reynolds number, Re, may be arbitrary low, the observed flow has all main features of developed turbulence, and can be compared to turbulent flow in a pipe at Re ≃ 10 5 [1,2].

EPL, Jul 1, 2014

We present experimental observations and numerical simulations of a wrinkling instability that oc... more We present experimental observations and numerical simulations of a wrinkling instability that occurs at sufficiently high strain rates in the trembling regime of vesicle dynamics in steady linear flow. Spectral and statistical analysis of the data shows similarities and differences with the wrinkling instability observed earlier for vesicles in transient elongation flow. The critical relevance of thermal fluctuations for this phenomenon is revealed by a simple model using coupled Langevin equations that reproduces the experimental observations quite well.

arXiv (Cornell University), Dec 2, 2021

Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent str... more Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent stretching can result in the coil-stretch transition. This phenomenon has been characterized by using the formalism of nonequilibrium statistical mechanics. In particular, the entropy of the polymer extension reaches a maximum at the transition. We extend the entropic characterization of the coil-stretch transition by studying the differential entropy of the polymer fractional extension in a set of laminar and random velocity fields that are benchmarks for the study of polymer stretching in flow. In the case of random velocity fields, a suitable description of the transition is obtained by considering the entropy of the logarithm of the extension instead of the entropy of the extension itself. Entropy emerges as an effective tool for capturing the coil-stretch transition and comparing its features in different flows.

Physical Review E, May 18, 2012

We report the experimental studies on interaction of two vesicles trapped in a micro-fluidic four... more We report the experimental studies on interaction of two vesicles trapped in a micro-fluidic fourroll mill, where a plane linear flow is realized. We found that the dynamics of a vesicle in tanktreading motion is significantly altered by the presence of another vesicle at separation distances up to 3.2 ÷ 3.7 times of the vesicle effective radius. This result is supported by measurement of a single vesicle back-reaction on the velocity field. Thus, the experiment provides the upper bound for the volume fraction φ = 0.08 ÷ 0.13 of non-interacting vesicle suspensions.

Advances in Colloid and Interface Science, Jun 1, 2014

We review the dynamical behavior of giant fluid vesicles in various types of external hydrodynami... more We review the dynamical behavior of giant fluid vesicles in various types of external hydrodynamic flow. The interplay between stresses arising from membrane elasticity, hydrodynamic flows, and the ever present thermal fluctuations leads to a rich phenomenology. In linear flows with both rotational and elongational components, the properties of the tank-treading and tumbling motions are now well described by theoretical and numerical models. At the transition between these two regimes, strong shape deformations and amplification of thermal fluctuations generate a new regime called trembling. In this regime, the vesicle orientation oscillates quasi-periodically around the flow direction while asymmetric deformations occur. For strong enough flows, small-wavelength deformations like wrinkles are observed, similar to what happens in a suddenly reversed elongational flow. In steady elongational flow, vesicles with large excess areas deform into dumbbells at large flow rates and pearling occurs for even stronger flows. In capillary flows with parabolic flow profile, single vesicles migrate towards the center of the channel, where they adopt symmetric shapes, for two reasons. First, walls exert a hydrodynamic lift force which pushes them away. Second, shear stresses are minimal at the tip of the flow. However, symmetry is broken for vesicles with large excess areas, which flow off-center and deform asymmetrically. In suspensions, hydrodynamic interactions between vesicles add up to these two effects, making it challenging to deduce rheological properties from the dynamics of individual vesicles. Further investigations of vesicles and similar objects and their suspensions in steady or time-dependent flow will shed light on phenomena such as blood flow.

Nature Communications, Feb 26, 2019

Electron transport in two-dimensional conducting materials such as graphene, with dominant electr... more Electron transport in two-dimensional conducting materials such as graphene, with dominant electron-electron interaction, exhibits unusual vortex flow that leads to a nonlocal currentfield relation (negative resistance), distinct from the classical Ohm's law. The transport behavior of these materials is best described by low Reynolds number hydrodynamics, where the constitutive pressure-speed relation is Stoke's law. Here we report evidence of such vortices observed in a viscous flow of Newtonian fluid in a microfluidic device consisting of a rectangular cavity-analogous to the electronic system. We extend our experimental observations to elliptic cavities of different eccentricities, and validate them by numerically solving bi-harmonic equation obtained for the viscous flow with no-slip boundary conditions. We verify the existence of a predicted threshold at which vortices appear. Strikingly, we find that a two-dimensional theoretical model captures the essential features of three-dimensional Stokes flow in experiments.

Journal of Fluid Mechanics, May 5, 2022

We examine the response of an inertialess viscoelastic channel flow to localized perturbations. W... more We examine the response of an inertialess viscoelastic channel flow to localized perturbations. We thus performed an experiment in which we perturbed the flow using a localized velocity pulse and probed the perturbed fluid packet downstream from the perturbation location. While for low Weissenberg numbers the perturbed fluid reaches the measurement location as a single velocity pulse, for sufficiently high Weissenberg numbers and perturbation strengths, a random number of pulses arrive at the measurement location. The average number of pulses observed increases with the Weissenberg number. This observation constitutes a transition to a novel elastic pulse-splitting regime. Our results suggest a possible new direction for studying the elastic instability of viscoelastic channel flows at high elasticity through the growth of localized perturbations.

Rotating Rayleigh-Bénard convection: Küppers-Lortz transition

Physica D: Nonlinear Phenomena, Aug 1, 1991

Abstract Rayleigh-Bénard convection with rotation about a vertical axis is investigated for small... more Abstract Rayleigh-Bénard convection with rotation about a vertical axis is investigated for small dimensionless rotation rates 0< Ω< 50. The convection cell is cylindrical with aspect ratio Γ= 10 and the convecting fluid is water with a Prandtl number of 6.8 at T= 23.8 C. ...

Physical review fluids, Oct 15, 2018

Creeping flow of polymeric fluid without inertia exhibits elastic instabilities and elastic turbu... more Creeping flow of polymeric fluid without inertia exhibits elastic instabilities and elastic turbulence accompanied by drag enhancement due to elastic stress produced by flow-stretched polymers. However, in inertia-dominated flow at high Re and low fluid elasticity El, a reduction in turbulent frictional drag is caused by an intricate competition between inertial and elastic stresses. Here, we explore the effect of inertia on the stability of viscoelastic flow in a broad range of control parameters El and (Re, Wi). We present the stability diagram of observed flow regimes in Wi -Re coordinates and find that instabilities' onsets show unexpectedly non-monotonic dependence on El. Further, three distinct regions in the diagram are identified based on El. Strikingly, for high elasticity fluids we discover a complete relaminarization of flow at Reynolds number of the order of unity, different from a well-known turbulent drag reduction. These counterintuitive effects may be explained by a finite polymer extensibility and a suppression of vorticity at high Wi. Our results call for further theoretical and numerical development to uncover the role of inertial effect on elastic turbulence in a viscoelastic flow.

Physical review fluids, Oct 16, 2018

We report quantitative evidence of mixing-layer elastic instability in a viscoelastic fluid flow ... more We report quantitative evidence of mixing-layer elastic instability in a viscoelastic fluid flow between two widely spaced obstacles hindering a channel flow at Re 1 and W i 1. Two mixing layers with nonuniform shear velocity profiles are formed in the region between the obstacles. The mixing-layer instability arises in the vicinity of an inflection point on the shear velocity profile with a steep variation in the elastic stress. The instability results in an intermittent appearance of small vortices in the mixing layers and an amplification of spatio-temporal averaged vorticity in the elastic turbulence regime. The latter is characterized through scaling of friction factor with W i, and both pressure and velocity spectra. Furthermore, the observations reported provide improved understanding of the stability of the mixing layer in a viscoelastic fluid at large elasticity, i.e. W i 1 and Re 1, and oppose the current view of suppression of vorticity solely by polymer additives.

Physical Review E, Nov 29, 2012

Physics of Fluids, Apr 1, 2012

The influence of symmetrical non-Oberbeck-Boussinesq (SNOB) effect on statistical and scaling pro... more The influence of symmetrical non-Oberbeck-Boussinesq (SNOB) effect on statistical and scaling properties of temperature field in turbulent convection is investigated experimentally in SF 6 in the vicinity of its gas-liquid critical point (CP). The main conclusion of the studies is that besides the strong Ra and P r dependence of the rms of temperature fluctuations normalized by the temperature difference across the cell, different from the Oberbeck-Boussinesq (OB) case of turbulent convection, all rest of statistical and scaling properties of temperature field discussed in details are the same as in the OB case.

Physical review fluids, Jun 15, 2022

In this paper, we present experimental results and reveal that strong perturbations are not neces... more In this paper, we present experimental results and reveal that strong perturbations are not necessary for elastic instability to occur in straight-channel, inertialess, viscoelastic flows at high elasticity. We show that a non-normal-mode bifurcation is followed by chaotic fluctuations, self-organized as streamwise streaks, and elastic waves due to weak disturbances generated by a small cavity at the center of the top channel wall. The chaotic flow persists in the transition, elastic turbulence, and drag reduction regimes, in agreement with previous observations for the case of strong perturbations at the inlet. Furthermore, the observed elastic waves propagate in the spanwise direction, which allows us to confirm the elastic waves' linear dispersion relation directly. In addition, the spanwise propagating elastic wave's velocity depends on Weissenberg number with the same scaling that was previously observed for streamwise propagating waves, although their velocity magnitude is significantly smaller than what was previously observed for the streamwise ones.

Physical Review E, Nov 28, 2011

We report detailed quantitative studies of elastic turbulence in a curvilinear channel flow in a ... more We report detailed quantitative studies of elastic turbulence in a curvilinear channel flow in a dilute polymer solution of high molecular weight polyacrylamide in a high viscosity water-sugar solvent. Detailed studies of the average and rms velocity and velocity gradients profiles reveal an emergence of the boundary layer associated with the nonuniform distribution of the elastic stresses across the channel. The characteristic boundary width is independent of the Weissenberg number W i and proportional to the channel width that follows from our early investigations of the boundary layer in elastic turbulence of different flow geometries. The appearance of the characteristic spatial scales of the order of the boundary layer width of both velocity and velocity gradient in the correlation functions of the velocity and velocity gradient fields in a bulk flow suggests that rare and strong parcels of excessive elastic stresses, concentrated in the boundary layer, are ejected into the bulk flow similar to jets observed in passive scalar mixing. And finally, the experimental results show that one of the main predictions of the theory of elastic turbulence, namely the saturation of the normalized rms velocity gradient in the bulk flow of elastic turbulence contradicts to the experimental observations both qualitatively and quantitatively in spite of the fact that the theory explains well the observed sharp decay of the velocity power spectrum. The experimental findings call for further development of theory of elastic turbulence in a bounded container, similar to what was done for a passive scalar problem.

Physical review fluids, May 17, 2023

Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent str... more Polymers in non-uniform flows undergo strong deformation, which in the presence of persistent stretching can result in the coil-stretch transition. The statistics of polymer deformation depends strongly on the nature and the properties of the flow. Sultanov et al. [Phys. Rev. E 103, 033107 (2021)] have characterized the coil-stretch transition in an elastic turbulence of von Kármán flow by measuring the entropy of polymer extension as a function of the Weissenberg number. The entropic characterization of the coil-stretch transition is here extended to a set of laminar and random velocity fields that are benchmarks for the study of polymer stretching in flow. In the case of random velocity fields, a suitable description of the transition is obtained by considering the entropy of the logarithm of the extension instead of the entropy of the extension itself. Entropy emerges as an effective tool for capturing the coil-stretch transition and comparing its features in different flows.

Bulletin of the American Physical Society, Nov 20, 2006

Fluid vesicle dynamics and interaction in shear flow. VASILIY KANTSLER, ENRICO SERGE, VICTOR STEI... more Fluid vesicle dynamics and interaction in shear flow. VASILIY KANTSLER, ENRICO SERGE, VICTOR STEINBERG, DEPARTENT OF PHYSICS OF COMPLEX SYSTEMS TEAM -We present experimental results on single vesicle behavior subjected to shear flow, as well as the hydrodynamic interaction between neighboring vesicles. Moreover the dynamics of a vesicle in many-vesicle field is also studied. Tank treading, trembling and tumbling regimes of the motion are described in terms of the dimensionless variables, such as viscosity contrast, excess area and the dimensionless shear. It should be emphasized that vesicle interaction considerably increases tank treading angle fluctuations, though suppressing the transition to tumbling motion.

Bulletin of the American Physical Society, Mar 10, 2008

The properties of elastic turbulence in semi-dilute polymer solutions YONGGUN JUN, Physics of Com... more The properties of elastic turbulence in semi-dilute polymer solutions YONGGUN JUN, Physics of Complex Systems, Weizmann Institute of Science, VICTOR STEINBERG -We studied elastic turbulence in Karman swirling flow of semi-dilute polymer solution. The concentrations of polymer solution used in the experiment were 100, 300, 500, 700, and 900 ppm, and the velocity fields to calculate the rms of the gradients of the tangential velocity, ω rms , were obtained using PIV. First we checked the saturation of ω rms in the bulk, which represents the saturation of elastic stress. We found that W i bulk = ω rms τ saturates and approaches to unitary value as the polymer concentration increases. Here τ is the longest polymer relaxation time. Also we studied existence of the velocity boundary layer which is related to boundary layer of elastic stresses of elastic turbulence. The thickness of the boundary layer is the decreasing function of polymer concentration near the rotating upper plate but independent of concentrations near the wall.

arXiv (Cornell University), Sep 25, 2020

In the present study, we investigated flow structures and properties of elastic turbulence in str... more In the present study, we investigated flow structures and properties of elastic turbulence in straight 2D channel viscoelastic fluid flow and tested earlier observations. We discovered self-organized cycling process of weakly unstable coherent structures (CSs) of co-existing streaks and stream-wise vortices, with the former being destroyed by Kelvin-Helmholtz-like instability resulting in chaotic structures. The sequence periodically repeats itself leading to stochastically steady state. This selfsustained process (SSP) remarkably resembles one investigated theoretically and experimentally for Newtonian turbulence in straight channel flow. The unexpected new ingredient is the observation of elastic waves, which finds to be critical for existence of CSs and SSP generation due to energy pumping from large to smaller scales preceding sharp power-law decay in elastic turbulence energy spectrum. The reported finding suggests the universality of CSs in transition to turbulence via self-organized cycling (SSP) in linearly stable plane shear flows of both elastic and Newtonian fluids.

Physical Review Letters, May 16, 1988

A maior purpose of the Technical Information Center is to provide the broadest dissemination poss... more A maior purpose of the Technical Information Center is to provide the broadest dissemination possible of information contained in DOE's Research and Development Reports to business, industry, the academic community, and federal, state and local governments. Although a small portion of this report is not reproducible, it is being made available to expedite the availability of information on the research discussed herein.