Jet Of Viscous Fluid Research Articles

Electrospun Polycaprolactone Nanofibers: Current Research and Applications in Biomedical Application.

Unique mechanical properties, miscibility potency, and biodegradability are the three prominent features of polycaprolactone (PCL), making it an attractive biomaterial which commonly applied in regenerative medicine and biomedical engineering. Different strategies developed for fabricating nanofibrous construct, electrospinning is a practical, simple, and efficient technique based on electro-hydrodynamic systems that use an electrified viscous fluid jet drawn by the air toward a collector at a changing electric potential. PCL electrospun-based nanofibrous composites as proper scaffolds are employed in stem cell-related research, particularly in tissue engineering, wound dressing, and systems designed for sending drugs. A compilation of mechanochemical properties and most common biological performance on PCL-based electrospun fibrous structures in biomedical application are included in this study. Therefore, electrospun PCL nanofiber applying has been presented, and after that, current progress and prospects have been discussed. Literature reviews revealed that electrospun PCL nanofibrous composites had gained significant attention in regenerative medicine, and these structures have shown notable development in mechanobiological properties. This evidence is a crucial success for biomedical strategies, especially in regenerative medicine.

Obtaining Expressions for Time-Dependent Functions That Describe the Unsteady Properties of Swirling Jets of Viscous Fluid

Previously, it has been shown that the dynamic geometric configuration of the flow channel of the left heart and aorta corresponds to the direction of the streamlines of swirling flow, which can be described using the exact solution of the Navier–Stokes and continuity equations for the class of centripetal swirling viscous fluid flows. In this paper, analytical expressions were obtained. They describe the functions C0(t) and Γ0(t), included in the solutions, for the velocity components of such a flow. These expressions make it possible to relate the values of these functions to dynamic changes in the geometry of the flow channel in which the swirling flow evolves. The obtained expressions allow the reconstruction of the dynamic velocity field of an unsteady potential swirling flow in a flow channel of arbitrary geometry. The proposed approach can be used as a theoretical method for correct numerical modeling of the blood flow in the heart chambers and large arteries, as well as for developing a mathematical model of blood circulation, considering the swirling structure of the blood flow.

Fast waves development initiated by oscillations of a recoiling liquid filament in a viscous fluid jet

Fast waves development initiated by oscillations of a recoiling liquid filament in a viscous fluid jet

Liquid rope coiling: a synoptic view

In liquid rope coiling, a slender jet of viscous fluid falling onto a rigid surface builds a rotating corkscrew-like structure. Here, I use a numerical continuation method to construct a complete regime diagram for liquid rope coiling. I first consider the onset of coiling, and show that a suitable onset criterion is that the radius $a_{1}$ of the rope itself be just equal to the radius $R$ of the coil. Numerical calculation of the critical surface $a_{1}=R$ in the space of the dimensionless fall height $\unicode[STIX]{x1D6F1}_{H}$, flow rate $\unicode[STIX]{x1D6F1}_{Q}$ and nozzle diameter $\unicode[STIX]{x1D6F1}_{d}$ shows that the surface has four distinct asymptotic limits corresponding to a viscous (V) mode, a gravitational (G) mode and two inertial modes (I1, I2) which are distinguished by how much the tail of the jet is stretched by gravity. Exact expressions for the onset frequencies in each of these four modes are determined. Finally, the regime diagram is constructed in the form of contour plots of the dimensionless coiling frequency as a function of $\unicode[STIX]{x1D6F1}_{H}$ and $\unicode[STIX]{x1D6F1}_{Q}$ for several values of $\unicode[STIX]{x1D6F1}_{d}$. The diagram exhibits a total of six modes: V, G, I1, I2, a multivalued inertio-gravitational (IG) mode and a third inertial mode I3 with viscosity-dominated stretching of the tail. The regime diagram permits prediction of the coiling frequency for given values of the fall height, flow rate, viscosity and nozzle diameter, and should therefore be useful in practical applications ranging from non-woven textile production to 3D printing.

Delayed capillary breakup of falling viscous jets.

Thin jets of viscous fluid like honey falling from capillary nozzles can attain lengths exceeding 10 m before breaking up into droplets via the Rayleigh-Plateau (surface tension) instability. Using a combination of laboratory experiments and WKB analysis of the growth of shape perturbations on a jet being stretched by gravity, we determine how the jet's intact length l(b) depends on the flow rate Q, the viscosity η, and the surface tension coefficient γ. In the asymptotic limit of a high-viscosity jet, l(b)∼(gQ(2)η(4)/γ(4))(1/3), where g is the gravitational acceleration. The agreement between theory and experiment is good, except for very long jets.

Non-modal stability of round viscous jets

AbstractHydrodynamic stability of round viscous fluid jets is considered within the framework of the non-modal approach. Both the jet fluid and surrounding gas are assumed to be incompressible and Newtonian; the effect of surface capillary pressure is taken into account. The linearized Navier–Stokes equations coupled with boundary conditions at the jet axis, interface and infinity are reduced to a system of four ordinary differential equations for the amplitudes of disturbances in the form of spatial normal modes. The eigenvalue problem is solved by using the orthonormalization method with Newton iterations and the system of least stable normal modes is found. Linear combinations of modes (optimal disturbances) leading to the maximum kinetic energy at a specified set of governing parameters are found. Parametric study of optimal disturbances is carried out for both an air jet and a liquid jet in air. For the velocity profiles under consideration, it is found that the non-modal instability mechanism is significant for non-axisymmetric disturbances. The maximum energy of the optimal disturbances to the jets at the Reynolds number of 1000 is found to be two orders of magnitude larger than that of the single mode. The largest growth is gained by the streamwise velocity component.

Jet and Vortex Ring-Like Structures in Internal Combustion Engines: Stability Analysis and Analytical Solutions

Recently developed models, describing the disintegration of liquid jets and the dynamics of vortex ring-like structures at Die- sel and gasoline engine-like conditions, are reviewed. The results of comparative analysis of modal and non-modal hydrody- namic instabilities of round viscous fluid jets are presented. Analytical formulae for vortex ring translational velocities, pre- dicted by vortex ring models, are compared with the results of numerical solutions to the underlying equations and experimen- tal data. A new approach to numerical simulation of two-phase two-dimensional flows, based on a combination of the full La- grangian method for the dispersed phase and the vortex blob method for the carrier phase, is discussed.

Development of a new technique to generate microcapsules from the breakup of non‐Newtonian highly viscous fluid jets

AbstractA new method to produce microcapsules ranging from 300 to 700 μm based on the droplets formation from non‐newtonian high viscous liquids has been developed, characterized, and modeled. The technique involves the generation of a continuous high viscous solution jet, which is destabilized by means of a controlled vibration, breaking into droplets that undergo stabilization through a gelling process. Finally, the application of the wave‐mechanisms‐based theory to obtain a set of equations for the fitting of experimental data is assessed, as a first approximation for a better knowledge of the process. To find the fitting equations, the influence on the microcapsules size is studied through two‐dimensionless groups, the Ohnesorge and the Weber numbers, involving the liquid viscosity and flow, respectively, and determining their exponential dependences. Further coefficients are obtained by least‐squares fit of the experimental data. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Stability of a plane jet of a highly viscous fluid impinging on a horizontal solid wall

In a plane formulation, we consider a viscous-fluid jet flowing out of a rectangular channel and interacting with a horizontal solid substrate surface in the presence of gravity. The mathematical problem is formulated within the creeping flow approximation. For the numerical solution, a boundary-element method is used. The kinematic parameters of the jet and the evolution of the free surface are studied for different values of governing parameters. The critical values of the distance from the channel outlet to the solid wall are found. For the heights, greater than the critical value, the jet loses stability, which is manifested in the periodic buckling of the jet. A flow regime characterized by damped oscillations is described.

Analytical asymptotic solution of the problem of the nonlinear oscillations of a thick charged jet of viscous fluid

On the basis of second-order analytical asymptotic calculations the problem of the nonlinear oscillation of a uniformly charged jet of an electrically conductive viscous fluid is solved with account for the radial fluid velocity distribution in the jet. It is found that energy from the initially excited wave is gradually transmitted to a wave with double the wave number excited due to nonlinear interaction in the viscous jet, whereas in an ideal fluid the nonlinear correction amplitude is formed instantaneously at the initial instant.

Simulating and analysing Jackson Pollock's paintings

We present an interactive system which allows users to create abstract paintings mimicking the style of Jackson Pollock using 3D viscous fluid jets. Pollock's paintings were created by using streams of household paint to make guided, semi-random patterns on his canvas. Our fluid jet model consists of two coupled simulations: a Navier-Stokes solver for an axis-symmetric fluid column and a linked mass system for tracking the 3D motion of the jet's axis line. The paint trails left by the jets are represented using implicit surfaces. Our system also includes an algorithm for generating the splatter patterns created by the impacts of high-speed fluid drops. We allow users to analyse the fractal properties of the images they create, a concept inspired by the fractal properties that are believed to exist in Pollock's own paintings.

Asymptotic Theory of Stability of a Viscous Fluid Jet Ejected along a Wall

A linear and weakly nonlinear theory of stability of a laminar viscous fluid wall jet is considered. At large Reynolds numbers (calculated from the characteristic jet length) the undisturbed stationary flow is concentrated in a narrow region adjacent to the rigid surface. Nonstationary perturbations of this flow can be described by equations similar to the equations used in the theory of free interaction of a boundary layer. Such a description is made possible by introducing asymptotic order relations between the Reynolds number and the perturbation amplitudes and wavelengths. The set of solutions of the dispersion relation for the linear stability problem includes the eigenvalues of the phase velocities and wave numbers corresponding to the neutral and unstable perturbation modes. For finite fluctuation amplitudes, the evolution of the wave fields obeys the Korteweg-de Vries equations.

Stability of initially slow viscous jets driven by gravity

The stability of vertically falling viscous liquid jets issuing from a circular orifice with a low fluid velocity where the flow is dominated by viscous effects torn down by gravity leading to a flow dominated by inertia far downstream, is studied by means of linear stability analysis as well as direct numerical simulation of the one-dimensional model. Jet stability is also studied experimentally. Results for marginal stability and critical frequencies are in excellent agreement with our theoretical predictions. A new global instability of a viscous jet is found. This instability is observable whenever a falling liquid jet exhibits a long enough viscosity dominated region. The source of instability is surface tension. In contrast to the Rayleigh capillary instability that is always present, but leads to very long disintegration lengths in highly viscous fluid jets, the instability described here only occurs when the volume flux falls below a certain limit depending on the fluid properties and the nozzle diameter.

Drops: the collapse of capillary jets.

The appearance of fluid filaments during the evolution of a viscous fluid jet is a commonly observed phenomenon. It is shown here that the break-up of such a jet subject to capillary forces is impossible through the collapse of a uniform filament.

Flow visualization study of thermal counterflow jet in He II

A method of flow visualization in superfluid helium has been developed by the use of solid H 2D 2 particles and hollow glass spheres as neutrally buoyant tracers to follow the normal component flow. It is applied to the study of a thermal counterflow jet based on pattern recognition of jet profiles and on measurement of mean normal velocity. Traceability of both kinds of tracers is satisfactory up to a few cm s −1. The evolution of jet pattern is found to vary widely depending on the Reynolds number, quite similar to usual viscous fluid jets, ranging from laminar to fully turbulent ones. The large-scale vortical motion and the entrainment of the surrounding He II into jet are clearly seen in fully developed turbulent-like jets. The calculation of the total momentum flux from the normal fluid velocity profiles seems to indicate that the zero-relative-velocity situation between the normal and super components is reached in jets as suggested in previous experiments.

An energy loss coefficient in fluid buckling

A jet of viscous fluid falling against a flat plate may become unstable and buckle. The buckling process is postulated as a discontinuity, and a simple model is developed that indicates a loss of energy in the fluid buckling. Experimental values of the energy loss coefficient are presented.

Nonlinear capillary waves on a viscous fluid jet surface

Capillary instability of a fluid jet is one of the classical problems of hydrodynamics [1]. Studying it is of practical interest, particularly for the optimization of the ignition of a liquid propellant and the development of granulating apparatus in the chemical industry [2]. Until recently, the main attention has been paid to analyzing linear problems. Dispersion equations have been obtained for small perturbations of a jet surface with the viscosity of the external medium taken into account [3]. The construction of a theory of finite-amplitude waves on an ideal fluid jet surface was started in [4, 5]. Up to now this theory has achieved substantial results, as can be assessed by the successful numerical modeling of the dissociation of an inviscid fluid jet into drops [6] (see [7, 8] also). This paper is devoted to a discussion of the nonlinear development stage of viscous fluid jet instability under conditions allowing the influence of the surrounding medium and the gravity field to be neglected.

Numerical investigation of the tangential twist of an incompressible viscous fluid jet

The problem of the formation of eddy flow of tangential twist is examined. The fluid flow mode is laminar. The flow parameters are found by the numerical solution of the complete system of Navier-Stokes equations.

Breakup of a cylindrical viscous fluid jet under asymmetrical perturbations

Breakup of a cylindrical viscous fluid jet under asymmetrical perturbations