Surfactant-based, SB fluids exhibit complex rheological behavior due to substantial structural changes caused by the molecules self-assembled colloidal aggregation. Temperature and salinity affect their rheology and flow properties. In this study, both rheological and viscoelastic properties for the optimum concentration, 4%, of Aromox ® APA-T viscoelastic surfactant (VES) were investigated using two brine solutions; 2 and 4% KCl and wide range of temperatures (72°F – 200°F). Flow properties were examined using a 1/2-in. straight and coiled tubing (CR = 0.019). The results show that increasing solution salinity promotes formation of rod-like micelles and increases its flexibility. Salinity affects micelles growth and their rheological and viscoelastic behavior is very sensitive to the nature and structure of the added salt. Different molecular structures are formed; spherical micelles occur first and then increased temperature and/or salinity promotes the formation of rod-like micelles. Later, rod-like micelles are aligned in the flow direction and form a large super ordered structure of micellar bundles or aggregates called shear induced structure (SIS). Different structures implies different rheological and flow properties. Likewise, rheology improves with increasing temperature up to 100°F. Further increase in temperature reverses the effects and viscosity decreases. In addition, drag reduction and flow characteristics of SB fluids are improved by the addition of salt and/or increasing temperature up to 100°F. Results obtained are in full agreement with rheological and viscoelastic behavior of SB fluids for both salinity and temperature.

Pluronic F127 is a thermoresponsive hydrogel well used for various pharmaceutical applications. An emulsion of F127 can be gelated by heating the mixture, and this thermoresponsive gelation property enables local drug delivery. Thus, it is important to measure the gelation temeperature of F127 and similar thermoresponsive hydrogels for characterizing their gelation process for such applications. Gelation temperature ( T gel ) is a temperature threshold indicating the presence of network formation in F127 and similar thermoresponsive hydrogel materials. A widely used method for T gel measurement is to measure T gel based on changes in the storage modulus ( G′ ) and loss modulus ( G″ ) of the hydrogel with respect to temperature. However, this rheological measurement requires careful choices of measurement conditions. In this paper, we present the detailed tuning steps and results of our rheological T gel measurement of F127 using a rotational rheometer as a tutorial for other researchers. First, oscillation strain sweep measurements were performed to determine an optimum strain value in the linear viscoelastic region. Second, oscillation frequency sweep measurements were conducted to choose a reasonable oscillation frequency value. Third, G′ and G″ of F127 (25% w/v) were measured in the oscillation temperature sweep mode for the temperature range of 5°C to 45°C with the determined shear strain (0.1%) and oscillation frequency (1 rad/s). Last, T gel was determined based on the crossover between measured G′ and G″ curves. Additionally, we compared the temperature sweep mode and the temperature ramp mode, and investigated effects of preshearing duration on repeated G′-G″ measurement and T gel determination. The summarized procedure can be used as a reference to perform reliable and repeatable rheological T gel measurement of thermoresponsive hydrogel materials.

The phenomenon known as Toms effect can impart viscoelasticity to a water flow when a small amount of water-soluble polymer is added. The resulting viscoelastic fluid generates viscoelastic stress in the flow, dramatically reducing the turbulent stress. In this study, the spatial distribution of velocity is measured using a stereo-PIV method in the streamwise-spanwise plane parallel to the wall. Modification of the near wall turbulence by the polymer solution blown slowly from a permeable wall was investigated by analyzing the velocity distribution acquired by stereo-PIV measurements. Experimental results reveal that streamwise local mean velocity decreases as the dosed polymer concentration increases. The skewness factor at this height shifts from 0 to positive by adding the polymer, which indicates intensified turbulent coherent structure. Moreover, the spatial two-point correlation function calculated from streamwise velocity fluctuations maintains its high correlation with the streamwise direction. It is consistent with the finding from the instantaneous velocity distribution, which shows that the flection of low-speed streaks is suppressed. Next, it is revealed that the normal velocity at the wall for low-speed fluid is decreased dramatically by polymer additives. Moreover, applying the quadrant analysis, it is confirmed that ejection events are suppressed with decreasing normal velocity at the wall. Suppression of ejection motion affects to the turbulence in the log law layer. We conclude that this is one reason that turbulence is suppressed in a wide range of the shear layer by polymer additives present only in the vicinity of the wall.

The addition of a small amount of surfactant into water induces viscoelasticity. In turbulent channel and pipe flows, the wall friction significantly decreases with the surfactant additive, but a heat-transfer reduction also occurs. On the other hand, a phenomenon is reported that the instantaneous main flow broadly meanders in space and time under a certain condition in the surfactant solution flow past a backward-facing step (BFS); thus, the mean Reynolds shear stress remarkably increases. The influence of such a phenomenon cannot be neglected in thermal fluid equipment with usually complicated configurations. Therefore, understanding this phenomenon in detail is important both academically and industrially. In this study, particle image velocimetry measurements were carried out in a viscoelastic BFS flow with meandering phenomenon at high Reynolds number. We focused on the turbulent structures in the flow fields and investigated the interrelationship among the spatial scales of the eddy structures, Reynolds shear stress, and meandering motion using a spatial two-point correlation function or conditional averaging. In the meandering condition, we revealed that the Reynolds shear stress due to the low-speed fluid that departs from the upper wall opposite the step across the main flow contributes the largest to the mean Reynolds shear stress value. Then, a secondary recirculation region appears near the upper wall, in addition to the primary recirculation region. A reverse flow is apt to occur when rapid deceleration and pressure rise happens due to the sudden expansion of the channel cross section. Therefore, flow separation occurs at the upper wall, and a large-scale circulation appears there. Such flow is caused by the relationship between the pressure rise and the momentum transfer between the flow and the wall. We can conclude that the condition where an unstable motion occurs is influenced by the concentration of the surfactant solution because the surfactant additive acts on the shear stress.

The heat transport phenomena in a developed thermal boundary layer of surfactant solution flow were investigated experimentally. The experiment was conducted under different surfactant additive concentrations. The temperature fluctuations in a thermal boundary layer in a smooth channel flow were measured by fine-wire thermocouple probe. Heat transfer reducing rate and temperature fluctuation characteristics including mean temperature distribution, intensity, wave form, spectral density function, and skewness factor were studied. The results showed that the turbulent transport is obstructed by additives, and the temperature field shows dramatic changes. High frequency component of temperature fluctuation of surfactant solution flow was decreased due to suppression of turbulence and viscoelasticity. Large temperature fluctuations occur in the thermal boundary layer because the development of the thermal boundary layer is obstructed, and large temperature fluctuations appear to concentrate the temperature gradient in the near-wall region (10 < y + < 60). In contrast, viscous sublayer expands due to viscoelasticity, and the temperature gradient and turbulence fluctuation are small in the near-wall region of y + < 10. As a result, two layers having significantly different characteristics seem to coexist. The heat transfer reduction is constant with variation of additive concentration condition, but heat transport phenomena were microscopically influenced by viscoelasticity.

It is known as the Toms effect that the wall friction coefficient is reduced by adding a small amount of polymer or surfactant into a water flow. In the drag-reducing flow, it is expected that a time scale of turbulent velocity fluctuation is changed by relaxation time due to viscoelasticity. In the present study, experimental analysis of the turbulent velocity fluctuation was performed with temporal characteristics in surfactant solution flow. The velocity fluctuations were measured by using a two-component laser Doppler velocimeter system on turbulent channel flow. And then, we performed statistical operation on those data and examined the time scale. From spectra analysis, it was found that very low frequency velocity fluctuations existed near the wall region in the surfactant solution flow. It was also revealed that the strong anisotropy occurred not only with the intensity but also with frequency distribution in turbulent velocity fluctuations. Moreover, the turbulence contributes nothing to the Reynolds shear stress and behaves as a wave motion. It was concluded that the turbulent eddies and viscoelasticity were two factors contributing to turbulent generation in the viscoelastic turbulent flow, with each factor having its own time scale.

We studied viscoelastic turbulent flow over a backward-facing step of the expansion ratio ER = 1.5 using DNS (direct numerical simulation) at a friction Reynolds number Re τ0 of 100. We chose the Giesekus model as a viscoelastic constitutive equation, and the Weissenberg number is Wi τ0 = 10 and 20. Visualized instantaneous vortices revealing that a few vortices occur only above the recirculation regions in the viscoelastic fluid flow compared to those in the Newtonian flow. This phenomenon might be caused by the fluid viscoelasticity that would suppress the Kelvin-Helmholz vortex emanating from the step edge. The reattachment length from the step is 6.80 h for the Newtonian fluid, 7.82 h for Wi τ0 = 10, and 8.82 h for Wi τ0 = 20, where h is the step height. In the mean velocity distributions normalized by maximum inlet velocity, we have observed no significant difference among the three fluids, except for region near the upper or bottom wall, i.e., the recirculation and recovery regions at the front and behind the reattachment point. The streamwise turbulent intensity u’ rms is weaken in the recirculation region of the viscoelastic flows. In terms of v’ rms , its magnitude in the recirculation region becomes largest in the case of Wi τ0 = 10, not for the Newtonian fluid flow or more viscoelastic case of Wi τ0 = 20.

PLA (Poly Lactic Acid) is a bio-sourced and a biodegradable polymer. It represents an interesting substitute for some petrochemical based polymers, especially because of its wide range of applications in the biomedical, agriculture and packaging fields. Unfortunately, PLA exhibits slow crystallization kinetics, limiting the amount of crystallinity in the final product, which is a handicap in order to extend its use. Many authors have investigated the crystallization of polymers; nevertheless several physical mechanisms remain not yet understood. This work aims a complete characterization of PLA in order to improve the understanding of its crystallization kinetics. The quiescent crystallization was investigated using Differential Scanning Calorimetry (DSC) measurements in isothermal and non-isothermal conditions for PLA and PLA with 5wt % talc. The flow effect on crystallization was studied using a thermocontrolled hot-stage shearing device (Linkam) coupled with an optical microscope. The number of activated nuclei and the growth rate were measured as functions of temperature. In addition, the linear viscoelastic properties were obtained from a rheometer with plate-plate geometry. The enhancement of the crystallization was quantified and analyzed in terms of the half crystallization time t1/2. This characteristic time t1/2 is found to be drastically decreased by both the talc and the flow which promote supplementary nucleation leading to various crystalline microstructures. The flow is known to orient and stretch molecules leading to an extra nucleation. An original description of this phenomenon is proposed using two characteristic Weissenberg numbers; based on the definition of Rousse and reptation times. Finally, we have proposed a semi-empirical model to quantify the thermal and flow contributions on the crystallization.

In the present work, an additive-free new technique for enhancing the flow in pipelines is introduced. Such technique depends on inserting Turbulence Altering Pseudo-Surface, TAPS with certain dimensions inside the pipe (adjacent to the inner wall). Such technique is meant to simulate the viscoelastic behaviour of soluble additives to enhance the flow in pipelines. Liquid circulation system with a testing section divided into four subsections was used to test the drag reduction effect of the new technique. The results showed that almost 60% flow enhancement is achievable when inserting 12 strips with 60 cm length into 0.0381 m diameter pipe.

In this paper, the flow properties of several types of liquid passing through various sizes of micro-orifices were investigated. The jet thrust and pressure drops were measured for two polyethylene glycol solutions and four surfactant solutions. Different flow properties were found for the various surfactant solutions depending on the charge of the solute. For an anionic surfactant, the results were similar to those for water, whereas in the case of a cationic surfactant, both the jet thrust and pressure decreased greatly in comparison with the other test liquids. Finally, a nonionic surfactant exhibited a steep rise in the pressure drop at a particular value of the Reynolds number. In explaining this behavior, the liquid-solid interface and alignment of the surfactant molecules are considered, and consequently, it is strongly suggested that the elastic stress on elongational flows is a contributing factor. In addition, the decreases in pressure and thrust for polyethylene glycols are attributed to viscoelastic properties, regardless of the molecular weight of PEG.

Velocity vector fields around a falling sphere in a 1.0 wt % polyacrylamide (PAA) solution are obtained on a vertical cross section by particle image velocimetry (PIV). PAA solution is known as non-Newtonian fluid, which has shear thinning and viscoelastic property. Strain rate tensor fields and deformation fields are calculated from the velocity vector fields in order to visualize the dynamic behavior of the fluid quantitatively. In velocity vector field, two typical flow regions are observed in the wake of the sphere: approaching flow to the sphere, rising flow called “negative wake” [1]. Results show that the strain rate tensor field gives fluid strain at the approaching flow region and the edge of the negative wake. Furthermore deformation history of one portion of the fluid shows that fluid is strained in the approaching flow region, and the strain rate at the edge of the negative wake represents their recovery to the original status of the fluid in the moving frame.

The standard model for damping is the linear viscous dashpot which produces a force proportional to velocity. Although other sources of linear damping are known to exist, such as that due to viscoelasticity, it is not clear what range of mathematical forms damping models can take. Here it is suggested that there are only three types of damping model. These models are deduced by examining three configurations of mechanical components. These configurations include combinations of springs and dashpots and, most significantly, a semi-infinite beam. It is found that these models are best examined in the Laplace or s -plane so that features of the damping models may be expressed in terms of complex variable theory. The three types of damping model revealed by this analysis correspond to poles lying off the imaginary axis, poles on the negative real axis and pole like forms on the negative real axis that give rise to branch cuts. It is conjectured that these are the complete set of mathematical models that describe damping.

A Casson model is selected to describe the flow behavior of blood. Considering the viscoelasticity of protein film, and the finite deformation of protein bubble under the action of a Casson fluid, a nonlinear equation describing the dynamic behavior for a single protein bubble in blood is developed. The numerical method is used to study the effect of viscoelasticity of the protein film, the characteristic parameters of Casson fluid and the effect of surface tension on the dynamic behavior of protein bubble. The results show that, increasing the viscosity of Casson liquid will accelerate the amplitude decaying of protein bubble wall; the period becomes longer. In the condition that the viscosity of protein film is greater than that of Casson fluid, increasing the viscoelasticity of protein film will also accelerate the amplitude decaying of protein bubble wall. Further more, the greater the viscoelasticity of protein film is, the stronger its load bearing capacity is. Under the consideration of surface tension, the bubble wall will vibrate with higher decaying velocity of amplitude. Without considering the surface tension will lead to a greater relative deformation of protein bubble.

In polymer processing, it is established that the flow causes the polymer chains to stretch and store the energy, by changing their quiescent state free energy. Koscher et al. [1] presented in 2002 an experimental work concerning the flow induced crystallization. They made the assumption that the polymer melt elasticity, quantified by the first normal stress difference, is the driving force of flow-induced extra nucleation. In their work, a constant shear stress is considered, and the first normal stress difference agrees with the use of the trace of the stress tensor. The stored energy due to the flow “Δ Ge ” is commonly called elastic free energy and associated to the change in conformational tensor due to flow. By extending the Marrucci theory [2], several studies link this Δ Ge to the trace of the deviatoric stress tensor (first invariant). In this paper, a numerical model able to simulate polymer crystallization is developed. It is based on the assumption that flow induced extra nucleation is linked to the trace of the deviatoric stress tensor. Thus a viscoelastic constitutive equation, the multimode Upper Convected Maxwell (UCM) model, is used to express the viscoelastic extra-stress tensor τ VE , and a damping function is introduced in order to take into account the nonlinear viscoelasticity of the material. In Koscher’s work [1], the integral formulation of the Upper Convected Maxwell (UCM) model is used too, but without any damping function, i.e. they assume that the polymer behaves as linear viscoelastic. As an application, a 2D isothermal flow configuration between two plates is simulated. A comparison between the proposed model and the Koscher’s one is then performed, and interesting resultes are pesented: without introducing a damping function, the two models give similar results in the same configurations, but the introduction of a damping function leads to important discrepancies between the two models, seeming that the assumption of a linear viscoelastic behavior is not realistic when the fluid strain and/or stresses are greater than a given values.

Biomodels, which mimic the shape and motion of blood vessels, have been developed for clinical training in endovascular intervention and for the technical development of interventional devices such as stents. The present authors have developed a biomodel made of poly (vinyl alcohol) hydrogel (PVA-H), which has good transparency, low surface friction, and dynamic viscoelasticity similar to that of arteries. However, evaluation of its behavior as an arterial biomodel has not been carried out. In order to develop a PVA-H biomodel which can accurately mimic the motion of blood vessels, it is necessary to measure and match its mechanical properties in a tube shape mimicking blood vessels. In this study, tube-shaped PVA-H biomodels were prepared, and their mechanical properties were evaluated as to pulse wave velocity (PWV), compliance, and transfer function. PWV was calculated with Young’s modulus and dimensions of the biomodels. A tube-shaped PVA-H model and a model made of commercial silicone were set in a pulsatile flow path apparatus filled pure water (23°C). Sinusoidal pulsatile waves of various frequencies generated by a screw pump were released into flow path. The flow rate, the inner pressure, and the diameter of the biomodels were measured. The compliance of a biomodel was calculated with changing pressures and diameters. The transfer function was obtained as the ratio of the amplitude of the pressure in front of a biomodel and that behind it. The two kinds of biomodels studied showed PWV similar to that of real arteries: PVA-H shows lower PWV which younger arteries tend to show, while silicone shows higher PWV, similar to the case of aged arteries. In compliance, PVA-H shows a value similar to that of arteries in the lower pressure range, whereas silicone shows a value similar to that of arteries at higher pressure. A difference of transfer function in relation to the pulsatile frequencies was observed. This phenomenon is similar to that of real blood vessels and explainable in terms of the theory of the forced vibration in single-degree-of-freedom systems with attenuation. The transfer function is affected by mechanical properties of the wall, and the difference between biomodels is due to the viscoelasticity of the biomodels. With PVA-H, these parameters can be gradually changed by adjusting factors such as concentration. These findings indicate that PVA-H would be useful for the development of biomodels.

The non-Newtonian properties of blood, i.e., shear thinning and viscoelasticity, can have a significant influence on the distribution of Cerebral Blood Flow (CBF) in the human brain. The aim of this work is to quantify the role played by the non-Newtonian nature of blood. Under normal conditions, CBF is autoregulated to maintain baseline levels of flow and oxygen to the brain. However, in patients suffering from heart failure (HF), Stroke, or Arteriovenous malformation (AVM), the pressure in afferent vessels varies from the normal range within which the regulatory mechanisms can ensure a constant cerebral flow rate, leading to impaired cerebration in patients. It has been reported that the change in the flow rate is more significant in certain regions of the brain than others, and that this might be relevant to the pathophysiological symptoms exhibited in these patients. We have developed mathematical models of CBF under normal and the above disease conditions that use direct numerical simulations (DNS) for the individual capillaries along with the experimental data in a one-dimensional model to determine the flow rate and the methods for regulating CBF. The model also allows us to determine which regions of the brain would be affected relatively more severely under these conditions.

For the purpose of elucidating the mechanism of drag reduction by additives and finding a way to judge optimum drag-reducing additives through a simple rheological test, we performed DNS analysis of viscoelastic fluid turbulent flow in a two-dimensional channel. In this calculation, we employed the Giesekus constitutive equation to model the interaction between water-soluble polymer, or the elastic micellar network structure, and solvent. We calculated the fluid flow by varying the rheological parameters of the model. We examined the turbulent kinetic energy budget and studied the “viscoelastic contribution” term in the budget equation for turbulent intensity, which is not apparent in normal Newtonian fluid turbulence. Viscoelastic contribution has a characteristic effect on viscoelastic fluid turbulence. We concluded that the viscoelastic contribution plays a major role in turbulent frictional drag reduction. Dissipation and viscoelastic contribution serve as a key factor of turbulent kinetic energy loss in most areas of the channel. From the visualization of local and instantaneous eddy behavior, we discussed the relationship between viscoelastic contribution, elastic energy and turbulent production. We found that viscoelastic contribution serves as a direct local source of turbulent production, and that energy is stored in the elasticity.

We study the rimming flow of a viscoelastic film on the inner surface of a horizontal rotating cylinder. Simple lubrication theory is applied assuming that the Reynolds number is small and the liquid film is thin. For the steady-state flow of the Upper-Convected Maxwell (UCM) fluid the mathematical model reduces to a first order nonlinear ODE for the film thickness. We show that the liquid viscoelasticity changes the flow structure. In particular, the singularity observed for viscous liquids within the same lubrication approximation can be eliminated due liquid elasticity. We performed a detailed numeric analysis of the model and revealed some criticality regimes which are specific only for viscoelastic liquids.

A three dimensional front tracking finite difference method is used to study the deformation of a Newtonian drop suspended in an Oldroyd-B fluid undergoing a steady shearing motion. The change in drop deformation and orientation with increasing Deborah number is established for small to moderate deformations and explained by examining the elastic and viscous stresses at the interface. Significant change in the drop orientation with the flow direction, with increasing viscoelasticity is observed. A non-monotonic change in steady state drop deformation is observed with increasing Deborah number and explained in terms of the competition between increase due to localized polymer stretching at the drop tips and decrease due to change in drop orientation angle.

Wealky nonlinear stability analysis of thin viscoelastic liquid film flowing down a vertical wall including the phase change effects at the interface has been investigated. A normal mode approach and the method of multiple scales are employed to carry out the linear stability solution and the nonlinear stability solution for the film flow system. The results show that both the supercritical stability and subcritical instability are possible for condensate, evaporating and isothermal viscoelastic film flow system. The stability characteristics of the viscoelastic film flow are strongly influenced by the phase change parameter. The condensate (Evaporating) viscoelastic film is more stable (unstable) than the isothermal viscoelastic film and the effect of viscoelasticity is to destabilize the film flowing down a vertical wall.