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Dynamic behavior of complex shell structures is studied in the article using a programming and computing suite. The values of the lowest natural oscillation frequencies ωR1, ωR2 and the corresponding damping coefficients ωI1, ωI2 of the considered structure were determined using the developed methodology, depending on the parameter of structural non-homogeneity K. Based on the analysis of the research results, it was found that an increase in dissipative characteristics can be achieved by introducing additional viscous-elastic frames different from the characteristics of the inner and outer viscoelastic layers of the structure. Thus, it is possible to increase the efficiency of the synergistic effect of the viscoelastic properties of a structurally non-homogeneous system and reach the values of the defining coefficient of attenuation δ. [ABSTRACT FROM AUTHOR]

The understanding of a rapid mixing and mixing length of two substances is of great importance for the design of a subsonic combustor of a ramjet engine due to a very short residence time of the reactive flow. To investigate this problem, the complex shape of a combustion chamber is simplified as a two-dimensional coaxial gas-gas flow. The characteristics of a two-species compressible mixing layer is studied using an in-house solver together with a mass fraction model to represent differences in the density and viscosity of each gas. The results show that the mixing length increases with increased density and viscosity ratios. [ABSTRACT FROM AUTHOR]

The combined effect of rotation and magnetic field dependent viscosity (MgFDV) in porous media on the onset of convection in magnetic nanofluids (MgN f) using linear stability theory is considered. The work embodies three important slip mechanisms:(a)Brownian motion (b)thermophoresis (both are suggested by J. Buongiorno in his work Convective Transport in Nanofluids, 2006), and (c) magnetophoresis, which is included due to the appearance of magnetic nanoparticles. We make use of the Chebyshev pseudospectral QZ-method for working on the derived eigen value problem and represent the result for water based magnetic nanofluidsWb-MgN f and ester based magnetic nanofluidsℇb-MgN f for free-free boundaries in the gravity envi-ronment. The results for various important parameters governing the flow such as Taylor number Ta, Lewis number Le, Langevin parameter αL are represented through neutral stability curves (NsCurves) and critical stability curves (CsCurves). It is observed that the two significant parameters of the problem viz., rotation and MgFDV both contibute in delaying the onset of convection. Also, Le, αL and Δφ assist in maintaining the stability of the system. [ABSTRACT FROM AUTHOR]

Currently accepted turbulence theory assumes that the flow is continuum at all length scales, including the smallest length scale of turbulence, known as the Kolmogorov scale. Kolmogorov in his celebrated 1941 theory [A. N. Kolmogorov, C. R. Acad. Sci. URSS 30, 301-305 (1941)] asserted that the fine-scale turbulent structures in the energy cascade are universal. According to Kolmogorov's theory, the energy dissipation rate and kinematic viscosity alone describe this universal behavior in terms of the Kolmogorov length, time, and velocity scales. However, it has been suggested [R. Betchov, J. Fluid Mech. 3, 205-216 (1957); D. Bandak, N. Goldenfeld, A. A. Mailybaev, and G. Eyink, Phys. Rev. E 105, 065113 (2022)] that thermal fluctuations, absent from the continuum description of gases, can terminate the energy cascade at a length scale larger than mean-free-path considerations alone would suggest. Additionally, for high-Mach-number turbulent flows, the Kolmogorov length scale can be comparable to the gas-molecule mean free path, which could induce noncontinuum molecular-level effects in the turbulent energy cascade. To investigate these two issues, compressible Taylor-Green vortex flow is simulated using the direct simulation Monte Carlo (DSMC) method and direct numerical simulations (DNS) of the Navier-Stokes equations. It is found that the molecular-gas-dynamics spectra grow quadratically with wavenumber in the dissipation range due to thermal fluctuations instead of decreasing exponentially as the continuum description predicts. Macroscopically, thermal fluctuations appear to break the flow symmetries and thereby produce different but statistically similar routes from the initial non-turbulent flow to the long-time turbulent flow. [ABSTRACT FROM AUTHOR]

The cylindrical Pirani gauge sensitivity under different conditions is studied in our previous paper. We are modeled the Pirani gauge as cylindrical Couette flow – one dimensional axis symmetrical problem by using a statistical method – Direct Simulation Monte Carlo (DSMC) and the Navier-Stokes-Fourier equations numerical solving. The purpose of this article is to study the cylindrical two-dimensional Taylor-Couette flow with finite length of rarefied gas. The suddenly temperature change of the inner cylinder wall (the fiber) is used to modeling the boundary conditions. The finite volume method and statistical modeling is used to study this problem. This paper is a continuation of our previous work which we extend the study using the NSF model and its numerical solution to assess the applicability of the obtained results. The state of the gas is studied over a long time period close to establishing a steady state in the previous work, while in this paper is studied the initial moment of occurrence and reflection of the wave from the other cylinder. The realization of such conditions is difficult technically feasible in some cases, but their set in mathematical model gives more opportunities to study the stability in the gaseous medium between the cylinders. [ABSTRACT FROM AUTHOR]

The Taylor-Couette flow between two concentric cylinders have been studied extensively in the fluid dynamics literature. Taylor-Couette flow is very important in fluid dynamics since it is simple and at the same time it displays all the regimes in general fluid flow. It is observed in the Taylor-Couette flow that for low Reynolds number static vortices are formed and when the Reynolds number crosses a threshold, waves are formed in the form of wavy vortex flow around the cylinder. This phenomenon is surprising and the formation of the waves have been studied experimentally and computationally using standard computational fluid dynamics software. However, no analytical expression for the speed of the waves have been arrived at. In this article, exact expressions for the phase velocity and group velocity of the waves in Taylor-Couette flow have been arrived at when both the cylinders are rotating at the same angular speed. Also, it has been shown in this work that the waves are in general transverse, damped and circularly polarized which corresponds very well to experimental studies. [ABSTRACT FROM AUTHOR]

The flow between two concentric cylinders, i.e., the Taylor-Couette flow, was investigated when only the inner cylinder rotates. Analysis of flow pattern with the Reynolds number was carried out by flow visualizations. Shear stress and energy loss distribution within Taylor-Couette column were determined. The characterization study was carried out by applying water and used cooking oil at volume ratio of 1:1, 1:3, 1:5, and 1:6. The inner cylinder was rotated at 400 rpm. It was found that optimal volume ratio for wastewater treatment was 1:1, shown by the phenomenon of Modulated Wavy Vortices flow regime. The highest Taylor number of 1.37x107 was also achieved in the volume ratio, while the shear stress was -3.32. [ABSTRACT FROM AUTHOR]

We have numerically simulated the unsteady heat transfer from the rotating circular cylinder heated with time-periodic pulsating temperature. The cylinder is impulsively rotating in both clockwise and anti-clockwise directions and is placed across the uniform viscous stream in an unconfined domain. The Navier-Stokes equations with energy formulation are discretized by using a higher-order compact (HOC) finite difference scheme on non-uniform polar grids. The discretized system is then solved by using the Bi-Conjugate Gradient Stabilized iterative method. The effect of various Reynolds numbers, rotational rates, and various parameters of time-periodic pulsating temperature on the forced convection is studied thoroughly. It is found that the transport phenomenon is completely different from the existing forced convection from a circular cylinder heated with a constant temperature. The rotational motion is found to influence the heat transfer drastically as compared to the fixed cylinder case. Also, the different directions of rotation added different complexity to the heat transfer. The backward heat transfer is observed and studied thoroughly within our scope. The range of parameters used for our present study are, Pr (Prandtl number) = 0.7, 60 ≤ Re (Reynolds number) ≤ 200, rotational rates, α = 1, −1, amplitude of temperature, a = 1.5 and period of temperature, 0.01 ≤ P ≤ 100.0. The study is based on isotherm patterns, local and time-averaged Nusselt numbers, and center-line temperature distribution. Overall, our present study adds several new findings related to this problem, which are not reported before. [ABSTRACT FROM AUTHOR]

With the increase in the depths of drilling for oil wells and the use of directional and horizontal drilling methods, the speed of moving the cutting rock to the surface of the well remains one of the main factors responsible for cleaning the bottom of the well, which is directly related to the cost, time, and quality of drilling in addition to operational problems including increased friction of the teeth of the hoof, stubbornness, and the closure of the well. Using ANSYS-Fluent (2019 R3) Eulerian-Eulerian (E-E) model, a numerical modeling was performed to test the factors affecting the drilling fluid's ability to quickly move pieces to the surface of the well. The factors that were studied included studying the effect of drilling fluid viscosity, flow rate, and drilling angle, plus the effect of temperature and decentralization of the drill pipe and rotational speed. A three-dimensional model is built consisting of two concentric cylinders, the inner cylinder rotation with dimensions (length 400 cm and diameter 5 cm), and the outer cylinder stationary (length 400 cm and diameter 10 cm). The simulation results showed that the factors affecting the cutting transfer have different effects among them on the cutting transport ratio. Increasing the flow velocity has the greatest impact on the ability to lift the cutting, while increasing the plastic viscosity is not a desirable way to clean the bottom of the well. The results also showed that the decentralization of the drilling pipe has a clear effect on the speed of the cutting transport, additionally, the increase in the temperature of the drilling fluid reduces the ability of the drilling fluid to clean the bottom of the well. The increase in the incline of the hoof after 60˚ improves the ability of the drilling fluid to clean the well. [ABSTRACT FROM AUTHOR]

In the current investigation, we have discussed the impact of viscous dissipation on the peristaltic motion of Carreau fluid through the tapered eccentric cylinders. We have also considered the incompressible Carreau fluid in between the two eccentric cylinders, here we have rigorous inner tube and tapered outer tube, and where the outer tube wall is subjected to a sinusoidal wave. The governing equation of continuity, momentum, and temperature are solved by applying analytic technique known as Homotopy Perturbation Method. The analytical determination of pressure rise and pressure gradients are achieved. The impacts of different specifications on temperature, pressure rise, and pressure gradient distributions are studied graphically. It is noticed that Diverging tapering attains more temperature as compared to converging tapering. Temperature increases with increase in Brinkman number Br. Pressure rise ΔPλ rises with rise in the Brinkman number (Br) as well as the increase in the azimuthal coordinate θ. Pressure gradient declines with rise in Brinkman number Br, and also noticed that there will be declination for rise in the value of δ0. [ABSTRACT FROM AUTHOR]

It is essential to determine the sensitivity and the inertia of the cylindrical Pirani gauge under different conditions when modeling it. For this purpose, it is appropriate to study the Taylor-Couette flow between two stationary concentric cylinders with finite length. In this work is considered the possibilities for instability and self-organization of the flow in the gaseous medium between the cylinders with the wall inhomogeneous temperature profile of the inner cylinder (the fiber). These processes can affect the accuracy and sensitivity of the gauge. The heat and the energy transfer in setting on different forms of temperature distributed on the inner cylinder in the form of stationary temperature are studied. The realization of such conditions is difficult technically feasible in some cases, but their set in mathematical model gives more opportunities to study the stability and the flow self-organization in the gaseous medium between the cylinders. [ABSTRACT FROM AUTHOR]

Modeling the Couette flow in a semicircular channel and experiments using hot-wires installed directly into the flow allowed to obtain new results on the flow structure, velocity fluctuations, Taylor-Görtler vortices for both laminar and turbulent regimes [1-3]. Data were also obtained for the distributed roughness created by two ways. For the first one a self-adhesive tape of 0.16 mm thickness and 15 mm width has been used along the generatrix of the rotating cylinder. It was possible to glue several layers so to increase the thickness of the protrusions up to 3 times. The number of the protrusions was 2 or 4. The second type of irregularities has been created with grooves. For this aim a 3D printer has been used to create inner rotating cylinder with 4 equispaced grooves. The depth of the grooves was varied up to 3.5 mm. The measurements were carried out at different flow Reynolds numbers, changed both by the cylinder rotation speed and by pressure inside the channel. The obtained from hot-wire measurement results contain the average velocity profiles, the velocity fluctuation profiles across the semicircular channel, the flow disturbance spectra and characteristic frequencies for many flow regimes. [ABSTRACT FROM AUTHOR]

The movement of air around a rotating milling cutter is investigated experimentally by using the optical non-intrusive method PIV (Particle Image Velocimetry). The milling cutter is located next to a flat surface simulating the processed material. The Flow is studied in three planes in axial × radial direction with phases 90°, 180° and 270° from the point closest to the flat desk. The PIV timing has been synchronized with the cutter rotation. We observed plumes governed by centrifugal force (as in Taylor-Couette flow) acting on the air teared with the rotating milling cutter. In average, the air flows along the milling cutter from its front end forming a large-scale vortex mostly apparent at higher velocity and at the plane opposite to the processed surface. At the 90°plane, the air is sucked towards the milling cutter, while at the 270°plane, the air is pushed away from it. Spatial correlation function shows a weak periodicity close to the cutter and widening of its shape with increasing distance from the milling cutter. [ABSTRACT FROM AUTHOR]

On the basis of our previous studies in the flow modeling of rarefied gas between coaxial cylinders under pulsating radial motion and pulsating temperature (one-dimensional problem), the energy transfer in the system of gas - surrounding cylinders is studied at the cylinders axis pulsating of the inner cylinders (two-dimensional problem). The energy transfer is modeled with a statistical DSMC model. The obtained results show how the external mechanical disturbances at the cylinder axis direction influence on the gas flow. These results make it possible to assess the gauge sensitivity under external mechanical disturbances. [ABSTRACT FROM AUTHOR]

On the basis of our previous studies in the flow modeling of rarefied gas between coaxial cylinders under different temperature and kinematic boundary conditions, the energy transfer in the system of gas - surrounding cylinders is studied in the radius pulsating of one of the cylinders. The energy transfer is modeled with continuous model based on Navier-Stokes-Fourier equations of motion and a statistical DSMC model. The obtained results show that the external mechanical disturbances in the radial direction influence more significantly the operation of the Pirani gauge when there is a difference in the temperature of the thread and the wall of the outer cylinder. These results make it possible to assess the gauge sensitivity under external mechanical disturbances. [ABSTRACT FROM AUTHOR]

Study on the application of Taylor-Couette column for emulsion liquid membrane system has been done. To optimise extraction process under TCC, a research to investigate effect of volume ratio of oil to water is of important. Fluid viscosity was examined by varying volume ratio of kerosene to water. TCC was characterised to determine flow regimes, shear stress, and energy loss distribution. Volume ratio of oil to water was varied at 1:1, 1:3, 1:5, and 1:6 while inner and outer cylinders speed were maintained constant at 31.4 and 0 rad/s, respectively. Investigation on the effect of volume ratio of oil to water towards flow regime ended to same flow regime of Turbulence Taylor Vortices (TTV). There was degradation of wall shear stress from 8.57x10-2 Pa to 7.42x10-2 Pa. [ABSTRACT FROM AUTHOR]

Application of scaffold technology for the problem of bone tissue regeneration has great prospects in modern medicine. The influence of fluid shear stress on stem cells cultivation and its differentiation into osteoblasts is the subject of intensive research. Mathematical modeling of fluid flow in bioreactor allowed us to determine the structure of flow and estimate the level of mechanical stress on cells. The series of computations for different rotation frequencies (0.083, 0.124, 0.167, 0.2 and 0.233 Hz) was performed for the laminar flow regime approximation. It was shown that the Taylor vortices in the gap between the cylinders qualitatively change the distribution of static pressure and shear stress in the region of vortices connection. It was shown that an increase in the rotation frequency leads to an increase of the unevenness in distribution of the above mentioned functions. The obtained shear stress and static pressure dependence on the rotational frequency make it possible to choose the operating mode of the reactor depending on the provided requirements. It was shown that in the range of rotation frequencies chosen in this work (0.083 < f < 0.233 Hz), the shear stress does not exceed the known literature data (0.002 - 0.1 Pa). [ABSTRACT FROM AUTHOR]

Numerical methods for solving convection-diffusion-reaction (CDR) scalar transport equation in three-dimensional flow are used in the present investigation. The flow is confined between two concentric cylinders both the inner cylinder and the outer one are allowed to rotate. Direct numerical simulations (DNS) have been achieved to study the effects of the gravitational and the centrifugal potentials on the stability of incompressible Taylor-Couette flow. The Navier-Stokes equations and the uncoupled convection-diffusion-reaction equation are solved using a spectral development in one direction combined together with a finite element discretization in the two remaining directions. The complexity of the patterns is highlighted. Since, it increases as the rotation rates of the cylinders increase. In addition, the effect of the counter-rotation of the cylinders on the mass transfer is pointed out. [ABSTRACT FROM AUTHOR]

Periodic vortex shedding behind a circular cylinder (Karman vortex) and Taylor vortices between two coaxial spheres are investigated by the DSMC method with an improved new collision scheme. The new collision scheme (U-system 3) that can deal with large cell dimensions conserves the total energy of each collision pair precisely during an intermolecular collision and the stability of the scheme improves furthermore. The lock-in phenomena in which a frequency of vortex production is synchronized with the frequency of the cylinder vibration are confirmed in the DSMC calculation. The U-system is also verified to be effective in the three-dimensional calculation of Taylor vortices between concentric spheres in which four vortices appear around its equator. [ABSTRACT FROM AUTHOR]

The Taylor-Couette problem for a rarefied gas is studied numerically by the direct simulation Monte Carlo method. The gas is supposed to be contained in an annular domain, bounded by two coaxial rotating cylinders and top and bottom (specularly reflecting) boundaries, and the flow is assumed to be steady and axisymmetric. Special attention is focused on the effect of rotation of the outer cylinder on the type of the induced Taylor-vortex flow. It is shown that different types of flow can coexist stably in a wide range of speeds of rotation of the inner and outer cylinders unless the outer cylinder is rotating fast in the opposite direction to the inner. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have investigated different temperature gradient effect on Taylor-Couette flow. The radius ratio and aspect ratio of the model was 0.825 and 48, respectively. Two heating exchangers were used for generating different temperature gradient. The flow regime in the Taylor-Couette flow was studied by increasing the Reynolds number. The results showed that: as Gr is increased, in helical vortex flow regime, the vortex with the same direction of convection flow increased in size, and the moving velocty also increased. It is also shown that the presence of temperature gradient increased the flow instability obviously as the Richardson number larger than 0.004 5. [ABSTRACT FROM AUTHOR]

One industrial process used by Nexter Munitions to manufacture pyrotechnical materials consists in preparing an emulsion of wax in TNT (2,4,6-trinitrotoluene) and adding Aluminium and ONTA (3-nitro-1,2,4-triazole-5-one) particles. When the suspension is homogeneous, it is allowed to flow by gravity through a pipe located at the bottom of the tank and to fill up a shell body. The suspension is characterized by a solid volume fraction of 53.4%, which leads to high viscosities. In some circumstances, the emptying time is prohibitively long and the economic profitability is reduced. This study has been performed to make the emptying time lower with the constraint of unchanged volume fractions and grains mean diameter. So, we investigated the influence of the grain size distribution on the suspension viscosity. Different samples of Aluminium and ONTA have been used, with rather small differences in grain size distributions. The suspensions have been prepared in the industrial tank and the flow cast times measured. It has been observed that they differ by one order of magnitude. To avoid situations with too high emptying times, a procedure has been implemented to make prior characterization of the suspension rheology. Because of particles sedimentation and emulsion destabilisation, the classical Couette rheometer is not adapted. So, we designed and built a small size tank (113 cm3), where the suspension is continuously stirred and kept homogeneous. The measurement of the torque and rotational speed together with the use of the Couette analogy allowed us to observe an Ostwald fluid behaviour (flow consistency index k, flow behaviour index n). For a better prediction, we established a correlation between the measured (k, n) values and the grain size distributions. We characterized each suspension by the ratio of [lowercase_phi_synonym] to [lowercase_phi_synonym]m, where [lowercase_phi_synonym] is the solid volume fraction (imposed by the commercial specifications) and [lowercase_phi_synonym]m is the maximum packing fraction. Because of the strong analogy between concrete and energetic paste, we chose the widely used De Larrard model to compute [lowercase_phi_synonym]m. A linear dependence between the ratio/and the indices k and n was observed. The second step was to provide an analytical expression for the flow cast time of a power-law suspension from a tank with given geometry. Considering the large difference between the industrial inner tank diameter and the evacuation pipe diameter, we assumed that all the pressure drop was located in the evacuation pipe. Then, extending the Hagen-Poiseuille equation to Ostwald fluid, we were able to predict the emptying time with the knowledge of kand n. Experimental and predicted emptying time are in very good agreement. This work helped the industrial manufacturer to divide the emptying time by a factor 12. [ABSTRACT FROM AUTHOR]

This paper presents a recent procedure for recovering the shear flow curve in Couette rheometer from torque-rotational velocity data. It is the purpose here to extend the previous works and to compare our predictions in shear flow curve recovery with previous solutions in shear rate determination. With this goal, synthetic and experimental data of yield stress materials in Couette system are presently investigated. [ABSTRACT FROM AUTHOR]

Many complex fluids often show original non linear responses when submitted to shearing forces. These non linear behaviors result from the coupling between the structure of the fluid and the flow and can sometimes lead to shear localization effects generally characterized by a splitting of the system into two macroscopic layers bearing different shear rates and stacked along the velocity gradient direction. In this work, we focus on the dynamics of the shear-banding flow of a semidilute wormlike micellar system made of cetyltrimethylammonium bromide with sodium nitrate in water. Using a Couette geometry, we showed recently that the interface between shear-bands becomes unstable and undulates with a wave vector along the vorticity axis. We also observed different patterns of spatio-temporal dynamics depending on the applied shear rate in the banding regime. Here we extend this study by following simultaneously the dynamics of the interface together with the dynamics of small reflecting tracers seeded in the sample. The organization of the tracers into stripes stacked along the vorticity direction strongly suggests that the flow is three-dimensional. Moreover, we show that the dynamics of the Taylor-like vortices is correlated with the one of the interface in the coexistence regime. [ABSTRACT FROM AUTHOR]

Shear banding of repulsive particulate suspensions in rotating Couette flow has been studied by self-consistent particle simulation. The fluid-particle interaction was considered in this algorithm by recursively solving the microscopic particle dynamics and macroscopic flow simulation. The tangential velocity profiles were non-homogeneous and the shear banding was clearly observed. The band formation was affected by shear rate as well as volume fraction. An optimum shear rate region was found where the shear banding was most pronounced. The banding was found to evolve with stress growth, and the final form of shear banding was dependent upon the degree of stress relaxation. The mechanism of the band formation was explained in terms of the fundamental forces acting on the particle system and fluid-particle interaction rather than yielding. [ABSTRACT FROM AUTHOR]

Recently proposed theories for shear banding in wormlike micellar solutions (WLMs) rely on a shear-induced isotropic-nematic (I-N) phase separation as the mechanism for banding. Critical tests of such theories require spatially-resolved measurements of flow-kinematics and local mesoscale microstructure within the shear bands. We have recently developed such capabilities using a short gap Couette cell for flow-small angle neutron scattering (flow-SANS) measurements in the 1–2 plane of shear with collaborators at the NIST Center for Neutron Research. This work combines flow-SANS measurements with rheology, rheo-optics and velocimetry measurements to present the first complete spatially-resolved study of WLMs through the shear banding transition for a model shear banding WLM solution near the I-N phase boundary. The shear rheology is well-modeled by the Giesekus constitutive equation, with incorporated stress diffusion to predict shear banding. By fitting the stress diffusivity at the onset of banding, the model enables prediction of velocity profiles in the shear banded state which are in quantitative agreement with measured flow-kinematics. Quantitative analysis of the flow-SANS measurements shows a critical segmental alignment for banding and validates the Giesekus model predictions, linking segmental orientation to shear banding and providing the first rigorous evidence for the shear-induced I-N transition mechanism for shear banding. [ABSTRACT FROM AUTHOR]

The cascade of transitions separating laminar and turbulent flow in the Taylor Couette geometry was examined with drag reducing polymer solutions in the regime where the magnitude of the elastic forces approaches that of the inertial forces, i.e. where the elasticity number (El) nears unity. The elasticity number, defined as the ratio of a polymeric time scale to the viscous time scale, greatly impacts the stability boundaries of isolated secondary flow features in both the co- and counter-rotating Taylor Couette flow regimes. It was previously shown that for dilute poly(ethylene oxide) solutions with El<1, the elasticity effect was non-monotonic, mode-dependent, and more significant for higher order states. In this study, Reinner vs Reouter stability planes generated at El∼1 in concentric, independently rotating cylinders of radius ratio 0.912 and aspect ratio of 60.7 are compared to previous maps generated in the inertia-dominated regime (El∼0). As a result, the importance of elasticity with solutions of similar diluteness is illuminated for various flow transitions, including transitions to axisymmetric, wavy, spiraling and/or turbulent modes. Changes in stability during adiabatic increases of the inner cylinder Reynolds number were determined using flow visualization and spectral analysis. All flow states are characterized by symmetry/symmetry breaking features as well as azimuthal and axial wave numbers using a combination of flow visualization in 2D planes of radial, axial, projected azimuthal and time dimensions. Polymeric solution characterization includes dynamic and steady shear and extensional flows, light scattering, and sessile drop experiments, and addresses such issues as chain scission, aggregation, and temperature dependence. [ABSTRACT FROM AUTHOR]

The effects of nonlinearities on the stability are explored for shear thickening fluids in the narrow-gap limit of the Taylor-Couette flow. A dynamical system is obtained from the conservation of mass and momentum equations which include nonlinear terms in velocity components due to the shear-dependent viscosity. It is found that the critical Taylor number, corresponding to the loss of stability of Couette flow becomes higher as the shear-thickening effects increases. The Taylor vortex structure emerges here which loses its stability through a Hopf bifurcation. Naturally, one expects shear thickening fluids to result in inverse dynamical behavior of shear thinning fluids. This study proves that it may not occur as expected everywhere in the bifurcation diagram. It is assumed that shear-thickening fluids behave exactly as opposite of shear thinning ones. [ABSTRACT FROM AUTHOR]

Quasistatic simulations show that the topological changes or plastic events that occur when an aqueous foam flows are confined within narrow regions. The width of these regions is shown to scale with a power of the polydispersity in bubble area. The exponent is one-half for linear Couette flow and one-fifth for Poiseuille flow. [ABSTRACT FROM AUTHOR]

Elongational deformation of single DNA molecules in a start-up Couette flow and its relaxation process after the cessation of the flow were investigated with fluorescence microscopy. To clarify the influence of chain interaction, a very dilute solution and a concentrated solution were tested. The concentrated solution was made by mixing labeled T4-DNA with unlabeled salmon-milt-DNA. In addition, the clearance between two plates at the flow section was varied to clarify the gap size effects. The elongation and orientation and relaxation process were observed directly subject to inception of Couette flow in solutions of varying polymer concentration. We found that the maximum length of DNA molecules becomes large and the relaxation time becomes long as concentration of solution increases. [ABSTRACT FROM AUTHOR]

We discuss in this work the validity of the theoretical solution of the nonlinear Couette flow for a granular impurity obtained in a recent work [preprint arXiv:0802.0526], in the range of large inelasticity and shear rate. We show there is a good agreement between the theoretical solution and Monte Carlo simulation data, even under these extreme conditions. We also discuss an extended theoretical solution that would work for large inelasticities in ranges of shear rate a not covered by our previous work (i.e., below the threshold value ath for which uniform shear flow may be obtained) and compare also with simulation data. Preliminary results in the simulations give useful insight in order to obtain an exact and general solution of the nonlinear Couette flow (both for a ≥=ath and a