non-Newtonian Jet Research Articles

Simulation of non-Newtonian gas-focused micro-jets in chocked gas flow regime

Stable liquid jets are crucial for successful serial crystallography experiments. They are produced from gas dynamic virtual nozzles (GDVNs), where the liquid from an inner capillary is focused by a co-flowing gas from an outer converging capillary. Our previously investigated non-Newtonian jets with incompressible and compressible focusing gas under atmospheric conditions were extended towards compressible chocked gas under vacuum conditions. An axisymmetric GDVN was considered with a fixed gas flow rate of 15 mg/min and liquid flow rate of 40 µl/min. A mixture formulation of the laminar compressible multiphase problem was solved within finite volume method and volume of fluid framework. The jet lengths, diameters, velocities, and temperatures were analysed as a function of the power-law non-Newtonian modification of reference water. It is observed that the jets under vacuum conditions are thinner for Newtonian and shear-thickening fluids than those in the atmosphere. The jet length increases from shear-thinning to shear-thickening rheology but is not affected by the pressure. The shear produced at the nozzle outlet is similar for both pressure conditions but increases in downstream directions for vacuum conditions. Gas expanding into vacuum cools by ~100-150 K while the temperature of the liquid jet drops only by a few K.

Inflow Conditions and the Flow Behavior of Submerged Annular Viscoplastic Non-Newtonian Jets

Abstract Submerged annular viscoplastic jet flows were studied numerically within the steady laminar flow regime. The impacts of inner-to-outer annular nozzle diameter ratio, and yield number, for uniform and fully-developed inflow conditions, were investigated. The extent of the outer recirculation region and recirculation intensities of both the central and outer regions were found to substantially diminish with the yield number, resulting in the elimination of recirculation throughout the whole flow field at high yield numbers. The axial penetration of the jet decreases with both the yield number and the annular diameter ratio. The impact of inflow conditions on the flow structure and decay characteristics of the jet are more pronounced at low yield numbers.

Non-Newtonian turbulent jets at low-Reynolds number

We perform direct numerical simulations of planar jets of non-Newtonian fluids at low Reynolds number, in typical laminar conditions for a Newtonian fluid. We select three different non-Newtonian fluid models mainly characterized by shear-thinning (Carreau), viscoelasticity (Oldroyd-B) and shear-thinning and viscoelasticity together (Giesekus), and perform a thorough analysis of the resulting flow statistics. We characterize the fluids using the parameter γ, defined as the ratio of the relevant non-Newtonian time scale over a flow time scale. We observe that, as γ is increased, the jet transitions from a laminar flow at low γ, to a turbulent flow at high γ. We show that the different non-Newtonian features and their combination give rise to rather different flowing regimes, originating from the competition of viscous, elastic and inertial effects. We observe that both viscoelasticity and shear-thinning can develop the instability and the consequent transition to a turbulent flowing regime; however, the purely viscoelastic Oldroyd-B fluid exhibits the onset of disordered fluid motions at a lower value of γ than what observed for the purely shear-thinning Carreau fluid. When the two effects are both present, an intermediate condition is found, suggesting that, in this case, the shear-thinning feature is acting against the fluid elasticity. Despite the qualitative differences observed in the flowing regime, the bulk statistics, namely the centerline velocity and jet thickness, follow almost the same power-law scalings obtained for laminar and turbulent Newtonian planar jets. The simulations reported here are, to the best of our knowledge, the first direct numerical simulations showing the appearance of turbulence at low Reynolds number in jets, with the turbulent motions fully induced by the non-Newtonian properties of the fluid, since the Newtonian case at the same Reynolds number is characterized by steady, laminar flow.

Performance of Two-Fluid Atomization of Gel Propellant

Two-fluid atomization of highly viscous and shear thinning non-Newtonian fluids must overcome the viscous resistance. Conventional air-blast atomizers address this requirement by operating at higher gas–liquid mass ratios (GLRs) at the cost of deteriorated efficiency. In this investigation, the atomization efficiency of a two-fluid atomizer is characterized. Fluidic design of the atomizer reduces the viscosity-induced dampening of disruptive inertia force and speeds up the breakup by providing kinetic energy of strategically positioned microjets of air. Three fluids of different viscosities and surface tensions were tested to examine the effects of properties on atomization efficiency. The presence of droplets and ligaments near the exit plane of the atomizer revealed that the atomizer enables prompt breakup of fluids without appreciable delay by viscosity. Consequently, it could break up complex non-Newtonian Jet A1 gel propellant with efficiency in the range of 0.015–0.1. Moreover, it is also capable of atomizing Newtonian fluids like water (high surface tension) with efficiency of 0.06–0.1 and Jet A1 (low surface tension) with efficiency of 0.02–0.08. Note that varied as ( to ) for the liquids tested in this work. The results of this investigation show that the deterioration in the performance of internally impinging atomizers at higher air and liquid throughputs is not determined by the viscosity of liquid but is predominantly due to the loss in kinetic energy of the excess air.

Visual analysis of droplet dynamics in large-scale multiphase spray simulations

We present a data-driven visual analysis approach for the in-depth exploration of large numbers of droplets. Understanding droplet dynamics in sprays is of interest across many scientific fields for both simulation scientists and engineers. In this paper, we analyze large-scale direct numerical simulation datasets of the two-phase flow of non-Newtonian jets. Our interactive visual analysis approach comprises various dedicated exploration modalities that are supplemented by directly linking to ParaView. This hybrid setup supports a detailed investigation of droplets, both in the spatial domain and in terms of physical quantities . Considering a large variety of extracted physical quantities for each droplet enables investigating different aspects of interest in our data. To get an overview of different types of characteristic behaviors, we cluster massive numbers of droplets to analyze different types of occurring behaviors via domain-specific pre-aggregation, as well as different methods and parameters. Extraordinary temporal patterns are of high interest, especially to investigate edge cases and detect potential simulation issues. For this, we use a neural network-based approach to predict the development of these physical quantities and identify irregularly advected droplets.Graphic

Application of shear-thinning and shear-thickening fluids to computational fluid mechanics of high-Reynolds impinging turbulent jets for cooling engineering

In the present paper a numerical study on the heat transfer from a heated flat plate to a shear-thinning/shear-thickening high-Reynolds impinging jet is developed. Only laminar jet flows have been considered in the literature to date for this type of application. This investigation is focused on the study of the impact of nozzle-to-plate distance, generation of swirl and Power Law flow index in the quantities of interest for heat transfer. It has been found that the cooling of the plate is highly influenced by the shear-thinning and shear-thickening behaviour of the working fluid. The most relevant conclusion is that surface-averaged heat transfer is enhanced by a shear-thinning fluid, but the cooling at the stagnation point is enhanced by a shear-thickening fluid. Mathematical correlations are also provided based on the training data generated in the present investigation. Surprisingly, there are no engineering applications nor studies using high-Reynolds non-Newtonian jet flows yet, so this novel numerical investigation intends to show the advantages/drawbacks of several configurations.

On forcespinning of nonlinear rotating jets of viscoelastic Boger fluids

• Strong tensile force or stretching force makes jet of Boger fluid very thin. • Jet in three-dimension moves much faster than jet in two-dimension. • Strong centrifugal force can make jet thinner with increasing arc length. • Three-dimensionality of jet & presence of gravity are destabilizing. • High rotation & viscoelasticity can make jet of Boger fluid very thin. We consider forcespinning (FS) of nonlinear three-dimensional rotating viscoelastic jets of Boger fluids and in the presence of gravity effect. In FS process, a fluid jet is forced through an orifice of a rotating spinneret leading to the formation of a curved jet. Applying the upper-convected Maxwell constitutive model for the stress tensor part of the governing non-Newtonian jet system and using scaling and perturbation methods, we develop a model for the jet system. We determine the nonlinear solutions for the jet quantities such as the radius, speed, stretching force, compressive force, tensile force and the jet centerline, and we calculate these quantities for different values of the jet arc length and the parameters representing rotation, viscoelasticity, gravity, surface tension and polymer viscosity. We find that the effects of rotation, relaxation time, gravity and three-dimensionality of the modeling system on the jet of Boger fluid can be significant. Beyond a very short distance from the jet exit, the jet speed, tensile force, stretching force and the jet curvature are notably increased and the jet radius is much reduced with increasing the viscoelasticity, rotation rate and the jet arc length. Strong tensile force or stretching force corresponds to weak compressive force and very thin jet of Boger fluid.

On Nonlinear Rotating Non-Newtonian Jets With Ambient Flows

Abstract We consider the problem of nonlinear rotating non-Newtonian jets in the presence of ambient flows. Using the original governing system of equations for such jet flows, we use scaling and perturbation techniques to reduce such system to a simplified one where the stress tensor is governed by Giesekus constitutive equations. We develop a method to take into account the effect of the ambient flow, which usually exists due to the externally imposed rotational constraint, on the formation of the non-Newtonian jet. We compute numerically the nonlinear steady solutions for the jet and determine expressions for the jet quantities like speed, stretching rate, radius, strain rate, and tensile force. These quantities are calculated for different values of the parameters such as those due to the ambient flow and viscoelasticity. We find that the ambient flow is stabilizing so that the strain rate, stretching rate, speed, and tensile force decrease with increase in the ambient flow effect, while the jet radius increases with such effect. The viscoelasticity of the fiber jet reduces notably the stabilizing effect of the ambient flow on the jet quantities, but the stabilizing effect of the ambient flow increases with the arc length of the jet centerline.

Instability of non-Newtonian liquid jets in centrifugal spinning with surfactants

Centrifugal spinning process is a novel method used to produce nanofibers. In this process, we focus on the temporal and spatial instability of slender non-Newtonian jets falling under gravity in the presence of centrifugal forces and surfactants. The effects of the surfactants on the trajectory of non-Newtonian jets in the centrifugal spinning have been shown using asymptotic and numerical approaches. Furthermore, the results obtained from the linear theory have been used to estimate the break-up lengths and droplet sizes of this study. Our results also show that surfactants can provide a possibility of further manipulating of the break-up and main droplets.

Linear stability analysis of a non-Newtonian liquid jet in a coaxial swirling air

The instability behavior of a power law liquid jet moving in a swirling air is investigated theoretically. The power law model is selected to describe the viscosity of the non-Newtonian jet. The corresponding dispersion relation is obtained by a linear stability analysis. Besides, the effects of air swirl strength, non-axisymmetric mode, liquid Weber number, generalized Reynolds number, power law index and consistency coefficient on the instability of the power law liquid jet surrounded by a swirling gas are studied in the Rayleigh and Taylor modes. The results show that the shear-thickening liquid jet is more unstable than the Newtonian and shear-thinning liquids when the air swirl is introduced. The air swirl is a stabilizing factor on the instability of the power law liquid jet in Rayleigh and Taylor modes. It is also found, when the air swirl is introduced, the maximum growth rate of the power liquid jet decreases as the liquid Weber number increases in Rayleigh mode, while it increases in Taylor mode. Moreover, the viscous forces of the liquid always prevent the jet from breaking up.

Linear temporal instability analysis of a non-Newtonian liquid jet containing cavitation bubbles

The temporal instability behavior of a non-Newtonian liquid jet in the presence of cavitation bubbles is investigated theoretically. The power law model is selected to describe the viscosity of the non-Newtonian jet. The unstable growth rate is obtained by Chebyshev collocation method. Besides, the effects of the compressibility of liquid, the compressibility of gas, the incorporating compressibility of both liquid and gas on the instability of the power law liquid jet are studied in this case. Especially, energy analysis is performed to study the breakup mechanism of the jet. The results show that the liquid compressibility is a unstable factor on the jet instability. However, the gas compressibility is the factor to prevent the jet from breaking. For the axisymmetric disturbance, it is noted that the viscous force always makes the jet being stable by energy analysis. But for the first asymmetric disturbance, there exists a turning point for the effect of viscosity of the liquid on the jet instability at a large wave number.

Predicting erosion in a non-Newtonian shear-thinning jet flow with validated CFD models from PIV and PTV measurements

In oil and gas industry, an increase in production is often achieved by injecting fracturing fluids with particles/proppants into rocks and reservoirs. There are various fracking fluids that oil and gas companies use, and some of these fracturing fluids demonstrate non-Newtonian flow behavior. In this paper, sand erosion behavior in shear-thinning carboxymethyl cellulose (CMC) solution is investigated with a jet impingement facility. Particularly, near wall flow speeds and particle impinging speeds are investigated in shear-thinning CMC fluids by Particle Image Velocimetery (PIV) and Particle Tracing Velocimetery (PTV) techniques. Computational Fluid Dynamics (CFD) are also used to predict the near wall particle impact information. The results indicate that different turbulence models resolve different near wall flow and particle impact characteristics. User Defined Functions (UDF) are developed and used to implement erosion ratio equations and simulate solid particle erosion behavior in the non-Newtonian fluid. The predictions are compared with experimental results. The results of this study can help improving erosion prediction in the hydraulic fracturing process utilizing CFD.

On nonlinear rotating electrified non-Newtonian jets

We consider a nonlinear non-Newtonian rotating jet flow whose centerline is curved and is elongated by an electric force due to an imposed electric field. The jet is driven both by the imposed electric and rotational forces. We introduce a non-Newtonian viscosity model, which, in particular, takes into account both extension thinning and thickening of the jet. From the governing equations and the boundary conditions of such jet flow, we construct a modeling system based on the slender-body theory for such nonlinear jet and calculate numerically the expressions for the nonlinear steady solutions for the jet quantities such as radius, speed, stretching rate, induced electric field and surface charge versus arc length. We determine these quantities for different values of the parameters that represent effects due to rotation, electric field, electric conductivity, viscosity and relaxation time. We find, in particular, that the jet speeds up, stretches up, and its diameter reduces significantly with increasing the imposed electric force, rotational forces and the jet relaxation time. The notable jet radius reduction that is due to strong electric and rotational effects is found to be for jet dominated by negative surface charge whose magnitude enhances with the rotation rate and the electrical conductivity.

Investigation of electrospun nanofibers with an electrified non-Newtonian jet using differential quadrature method

In this paper, the influence of non-Newtonian rheology of nanofibers on electrospinning process is analyzed numerically. A simple and highly accurate numerical method called the Differential Quadrature Method (DQM), is used for solving the governing equations of electrospinning systems. The validity of the results of DQM solution are verified via comparison with experimental data and a good agreement between the present method and the experimental data is observed. The behavior of the elongation, velocity, stress and total force profiles with variation of some physical parameters are discussed in details. The results show that by increasing the values of yield stress, the fluid elongation is reduced significantly. Furthermore, it is found that Differential Quadrature Method can be easily extended to other strongly nonlinear equations and can be found widely applicable in engineering and science.

Numerical study on polymer nanofibers with electrically charged jet of viscoelastic fluid in electrospinning process

Electrospinning is a useful and efficient technique to produce polymeric nanofibers. Nanofibers of polymers are electrospun by creating an electrically charged jet of polymer solution. Numerical study on non-Newtonian and viscoelastic jets of polymer nanofibers in electrospinning process is presented in this work. In particular, the effect of non-Newtonian rheology on the jet profile during the electrospinning process is examined. The governing equations of the problem are solved numerically using the Keller-Box method. The effects of yield stress and power-law index on the elongation, velocity, stress and total force are presented and discussed in detail. The results show that by increasing the values of yield stress, the fluid elongation is reduced significantly.

Numerical Investigation on Flow and Mixed convective Heat Transfer of Non-Newtonian Impinging Slot Jets

Mixed convection heat transfer of non-Newtonian impinging slot jets was investigated numerically. The simulation was performed using a temperature dependent power-law viscosity model. The results showed that for high Richardson numbers, a recirculation zone is created in the vicinity of impingement wall which prevents the jet stream from penetration into near wall region and decreases the Nusselt number around the stagnation point. The effects of jet-to-plate spacing, inlet Peclet number and the jet inlet width on the flow structure and heat transfer characteristics of impinging jet were studied using the numerical results. By decreasing jet-to-plate spacing and jet inlet width and increasing inlet Peclet number, the flow reversal in the vicinity of heated wall was disappeared and the local Nusselt number increases as a result of deeper penetration of jet stream the near wall region. Furthermore, the results indicated that the maximum local and average Nusselt numbers belong to the shear-thinning jets with minimum inlet width and the minimum jet-to-plate spacing.

The Flow and Decay Behavior of a Submerged Shear-Thinning Jet With Yield Stress

The flow and decay characteristics of submerged jets of shear-thinning fluids with yield stress are studied. Numerical solutions to the governing mass and momentum conservation equations, along with the Herschel–Bulkley rheological model, are obtained using a finite-difference scheme. A parametric study is implemented to investigate the influence of flow inertia and rheology over the following range of parameters: Reynolds number, 50 ≤ Re ≤ 200; yield number, 0 ≤ Y ≤ 1; and shear-thinning index, 0.6 ≤ n ≤ 1. A large recirculation region exists for Newtonian and shear-thinning non-Newtonian jets. However, the extent and strength of the recirculation region substantially diminish with the yield number and, to a lesser extent, when the shear-thinning index is reduced from 1 to 0.6. Increasing the yield number beyond a critical value eliminates flow recirculation. The centerline velocity and momentum decay of shear-thinning jets with yield stress, in general, increase with the yield number. Velocity- and momentum-based depths of penetration, DPU, and DPM, respectively, are introduced and presented. DPU and DPM are the downstream locations corresponding to 90% decay in the initial centerline velocity and jet momentum, respectively. A substantial decrease in DPU and DPM is observed when the shear-thinning index is reduced from 1 to 0.6 for Y = 0. The presence of yield stress significantly reduces both DPU and DPM of submerged jets. The impact of shear-thinning on the decay characteristics of the jet is more pronounced at low yield numbers.

Asymptotics and numerics for the upper-convected Maxwell model describing transient curved viscoelastic jets

This work deals with the modeling and simulation of non-Newtonian jet dynamics as it occurs in fiber spinning processes. Proceeding from a three-dimensional instationary boundary value problem of upper-convected Maxwell equations, we present a strict systematic derivation of a one-dimensional viscoelastic string model by using asymptotic analysis in the slenderness ratio of the jet. The model allows for the unrestricted motion and shape of the jet’s curve, and its deduction extends the hitherto existing uniaxial asymptotic approaches. However, the system of partial differential equations with algebraic constraint has a varying character (hyperbolic, hyperbolic–elliptic, parabolic deficiency). Its applicability range turns out to be limited depending on the physical parameters and the boundary conditions (i.e. singular perturbation). Numerical results are discussed for the hyperbolic regime of gravitational inflow–outflow set-ups which become relevant in drawing and extrusion processes. The simulations are performed with a normal form total upwind scheme in space and an implicit time-integration ensuring convergence of first order.

Break-up of a non-Newtonian jet injected downwards in a Newtonian liquid

The present work on downward injection of non-Newtonian jet is an extension of our recent work (Lakdawala et al, Int. J. Multiphase Flow. 59: 206–220, 2014) on upward injection of Newtonian jet. The non-Newtonian rheology of the jet is described by a Carreau type generalized Newtonian fluid (GNF) model, which is a phenomenological constitutive equation that accounts for both rate-thinning and rate-thickening. Level set method based numerical study is done for Newtonian as well as various types of shear thinning and thickening jet fluid. Effect of average injection velocity (V av, i ) is studied at a constant Reynolds number Re = 14.15, Weber number We = 1, Froude number Fr = 0.25, density ratio χ = 0.001 and viscosity ratio η = 0.01. CFD analysis of the temporal variation of interface and jet length (L j ) is done to propose different types of jet breakup regimes. At smaller, intermediate and larger values of V av, i , the regimes found are periodic uniform drop (P-UD), quasi-periodic non-uniform drop (QP-NUD) and no breakup (NB) regimes for a shear thinning jet; and periodic along with Satellite Drop (P +S), jetting (J) and no breakup (NB) regimes for a shear thickening jet, respectively. This is presented as a drop-formation regime map. Shear thickening (thinning) is shown to produce long (short) jet length. Diameter of the primary drop increases and its frequency of release decreases, due to increase in stability of the jet for shear thickening as compared to thinning fluid.

Velocity and Momentum Decay Characteristics of a Submerged Viscoplastic Jet

Velocity and momentum decay characteristics of a submerged viscoplastic non-Newtonian jet are studied within the steady laminar flow regime. The governing mass and momentum conservation equations along with the Bingham rheological model are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the influence of the initial velocity profile, flow inertia, and yield stress presence on the flow field characteristics. Two initial velocity profiles are considered, a top-hat and fully developed pipe jets. The centerline velocity decay is found to be more rapid for the pipe jet than the top-hat one when the fluid is Newtonian while the opposite trend is observed for yield stress Bingham fluids. The decay in the momentum flux of the pipe jet is always less than that of the top-hat jet. Momentum and velocity based jet depths of penetration are introduced and used to analyze the obtained flow field information for a wide range of Reynolds and yield numbers. Depths of penetration are found to linearly increase with the Reynolds number and substantially decrease with the yield number. The presence of yield stress significantly reduces the momentum and velocity penetration depths of submerged top-hat and pipe jets. Penetration depths of yield stress fluids are shown to be more than an order of magnitude smaller than the ones corresponding to Newtonian fluids.