scholarly journals Vorticity dynamics in a spatially developing liquid jet inside a co-flowing gas

2019 ◽  
Vol 877 ◽  
pp. 429-470
Author(s):  
A. Zandian ◽  
W. A. Sirignano ◽  
F. Hussain
Keyword(s):  
Liquid Velocity ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Three Dimensional ◽  
Upstream Region ◽  
Inertia Force ◽  
Liquid Jet ◽  
Viscous Forces ◽  
Surface Deformations ◽  
Axial Acceleration

A three-dimensional transient round liquid jet within a low-speed coaxial outer gas flow is numerically simulated and analysed via vortex dynamics ($\unicode[STIX]{x1D706}_{2}$ analysis). Two types of surface deformations are distinguished, which are separated by a large indentation on the jet stem. First, there are those inside the recirculation zone behind the leading cap – directly affecting the cap dynamics and well explained by the local vortices. Second, deformations upstream of the cap are mainly driven by the Kelvin–Helmholtz (KH) instability, unaffected by the vortices in the behind-the-cap region (BCR), and are important in the eventual atomization process. Different atomization mechanisms are identified and are delineated on a gas Weber number ($We_{g}$) versus liquid Reynolds number ($Re_{l}$) map based on the relative gas–liquid velocity. In a frame moving with the liquid velocity, this result is consistent with prior temporal studies. A simpler and clearer portrait of similarity of the atomization domains is shown by using the relative gas–liquid axial velocity, i.e. $We_{r}$ and $Re_{r}$, and avoiding the widely used velocity ratio as a third key parameter. A detailed comparison of vorticity along the axis in an Eulerian frame versus a frame fixed to a surface wave reveals that the vortex development and surface deformations are periodic in the upstream region, but this periodicity is lost closer to the BCR. In the practical range of the density ratio and for early times in the process, axial vorticity is mainly generated by baroclinicity while streamwise vortex stretching becomes more important at later times and only at lower relative velocities when pressure gradients are reduced. The inertia, vortex, pressure, viscous and surface tension forces are analysed to delineate the dominant causes of the three-dimensional instability of the axisymmetric KH structure due to surface acceleration in the axial, radial and azimuthal directions. The inertia force related to the axial gradient of kinetic energy is the main cause of the axial acceleration of the waves, while the azimuthal acceleration is mainly caused by the pressure and viscous forces. The viscous forces are negligible in the radial direction and away from the nozzle exit in the axial direction. It is interesting to note that azimuthal viscous forces are important even at high $Re_{l}$, indicating that inertia is not totally dominant in this instability occurring early in the atomization cascade.

The effect of air swirl profile on the instability of a viscous liquid jet

2000 ◽  
Vol 424 ◽  
pp. 1-20 ◽  
Author(s):  
Y. LIAO ◽  
S. M. JENG ◽  
M. A. JOG ◽  
M. A. BENJAMIN
Keyword(s):  
Viscous Liquid ◽  
Growth Rates ◽  
Axial Velocity ◽  
Weber Number ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Three Dimensional ◽  
Interfacial Instability ◽  
Liquid Jet ◽  
Axisymmetric Mode

A temporal linear stability analysis has been carried out to predict the instability of a viscous liquid jet surrounded by a swirling air stream with three-dimensional disturbances. The effects of flow conditions and fluid properties on the instability of the liquid jet are investigated via a parametric study by varying axial Weber number axial velocity ratio of the gas to liquid phase, swirl Weber numbers, density ratio and the Ohnesorge number. It is observed that the relative axial velocity between the liquid and gas phases promotes the interfacial instability. As the axial Weber number increases, the growth rates of unstable waves, the most unstable wavenumber and the unstable range of wavenumbers increase. Meanwhile, the increasing importance of helical modes compared to the axisymmetric mode switches the breakup regime from the Rayleigh regime to the first wind-induced regime and on to the second wind-induced regime. The predicted range of wavenumbers in which the first helical mode has higher growth rates than the axisymmetric mode agrees very well with experimental data. Results show that the destabilizing effects of the density ratio and the axial Weber number are nearly the same. Liquid viscosity inhibits the disintegration process of the liquid jet by reducing the growth rate of disturbances and by shifting the most unstable wavenumber to a lower value. Moreover, it damps higher helical modes more significantly than the axisymmetric mode. Air swirl has a stabilizing effect on the liquid jet. As air swirl strength increases, the growth rates of helical modes are reduced more significantly than that of the axisymmetric mode. The air swirl profile is found to have a significant effect on the instability of the liquid jet. The global, as well as local, effects of the swirl profile are examined in detail.

scholarly journals Stability of a Viscous Liquid Jet in a Coaxial Twisting Compressible Airflow

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 918
Author(s):  
Li-Mei Guo ◽  
Ming Lü ◽  
Zhi Ning
Keyword(s):  
Viscous Liquid ◽  
Axial Velocity ◽  
Liquid Velocity ◽  
Velocity Ratio ◽  
Dominant Mode ◽  
Liquid Jet ◽  
Axisymmetric Mode ◽  
Jet Instability ◽  
Jet Stability ◽  
Jet Breakup

Based on the linear stability analysis, a mathematical model for the stability of a viscous liquid jet in a coaxial twisting compressible airflow has been developed. It takes into account the twist and compressibility of the surrounding airflow, the viscosity of the liquid jet, and the cavitation bubbles within the liquid jet. Then, the effects of aerodynamics caused by the gas–liquid velocity difference on the jet stability are analyzed. The results show that under the airflow ejecting effect, the jet instability decreases first and then increases with the increase of the airflow axial velocity. When the gas–liquid velocity ratio A = 1, the jet is the most stable. When the gas–liquid velocity ratio A > 2, this is meaningful for the jet breakup compared with A = 0 (no air axial velocity). When the surrounding airflow swirls, the airflow rotation strength E will change the jet dominant mode. E has a stabilizing effect on the liquid jet under the axisymmetric mode, while E is conducive to jet instability under the asymmetry mode. The maximum disturbance growth rate of the liquid jet also decreases first and then increases with the increase of E. The liquid jet is the most stable when E = 0.65, and the jet starts to become more easier to breakup when E = 0.8425 compared with E = 0 (no swirling air). When the surrounding airflow twists (air moves in both axial and circumferential directions), given the axial velocity to change the circumferential velocity of the surrounding airflow, it is not conducive to the jet breakup, regardless of the axisymmetric disturbance or asymmetry disturbance.

Deformation and Surface Waves Properties of Round Nonturbulent Liquid Jets in Gaseous Crossflow

2005 ◽  
Author(s):  
C.-L. Ng ◽  
K. A. Sallam ◽  
H. M. Metwally ◽  
C. Aalburg
Keyword(s):  
Surface Waves ◽  
Weber Number ◽  
Computational Study ◽  
Density Ratio ◽  
Three Dimensional ◽  
Liquid Jets ◽  
Liquid Jet ◽  
Liquid Viscosity ◽  
Fluent Software ◽  
Wave Properties

A computational study of the deformation and surface wave properties of nonturbulent round liquid jets in gaseous crossflow is described. The objective of the study was to consider effects of liquid viscosity, liquid/gas density ratio, and crossflow Weber number that are representative of practical sprays. Three-dimensional computations of the deformation of round liquid jets in gaseous crossflow were carried out using FLUENT software utilizing its Volume of Fluid (VOF) module. The computations were evaluated satisfactorily based on earlier measurements of the properties of nonturbulent round liquid jets in crossflow (liquid jet deformation and surface waves) and revealed three-dimensional properties of the surface waves that could not be observed by previous measurements that were taken from the side of the jet.

A Quasi-Direct 3D Simulation of the Atomization of High-Speed Liquid Jets

2005 ◽  
Author(s):  
Gian Marco Bianchi ◽  
Piero Pelloni ◽  
Stefano Toninel ◽  
Ruben Scardovelli ◽  
Anthony Leboissetier ◽  
...  
Keyword(s):  
High Speed ◽  
Density Ratio ◽  
Three Dimensional ◽  
Liquid Jets ◽  
Liquid Jet ◽  
Nozzle Flow ◽  
Flow Conditions ◽  
Flow Perturbation ◽  
Spatially Correlated ◽  
Finite Volume Approach

In this paper a quasi-direct solution of transient three-dimensional CFD calculations based on a finite volume approach has been adopted to simulate the atomization process of high velocity liquid jets issuing an injector-like nozzle. An accurate Volume-of-Fluid (VOF) method is used to reconstruct and advect the interface between the liquid and gas phases. An extended mesh which includes the injector nozzle and the upstream plenum has been considered in order to investigate accurately the effect of nozzle flow conditions on the liquid jet atomization. Cavitation modeling has not been included in the present computations. Two different mean injection velocities, 150 m/s and 270 m/s, respectively, have been considered in the calculations as representative of semi-turbulent and fully-turbulent nozzle flow conditions. The liquid-to-gas density ratio is kept fixed at 57. The calculations show that atomisation is directly linked to the temporally and spatially correlated turbulence of the liquid jet. The bulk flow perturbation and the relaxation of the boundary layer have been found to be the basic mechanisms that generate surface perturbations of the liquid jet.

Spatiotemporal instability of a variable-density Batchelor vortex

2012 ◽  
Vol 703 ◽  
pp. 49-59 ◽  
Author(s):  
Bastien Di Pierro ◽  
Malek Abid
Keyword(s):  
Velocity Ratio ◽  
Density Ratio ◽  
Three Dimensional ◽  
Laboratory Frame ◽  
Variable Density ◽  
Constant Density ◽  
Azimuthal Mode ◽  
Linear Framework ◽  
High Reynolds ◽  
Absolute Transition

AbstractLinear and nonlinear impulse responses are computed, using three-dimensional numerical simulations, for an incompressible and variable density (inhomogeneous) Batchelor vortex at a moderately high Reynolds number, $\mathit{Re}= 667$. In the linear framework, the computed wavepacket is decomposed into azimuthal modes whose growth rates are determined along each spatiotemporal ray, in the laboratory frame. It is found that the Batchelor vortex undergoes a convective/absolute transition when the density ratio (inner/ambient), $s$, is varied solely (there is no need for an external counter flow to trigger this transition like that needed in the constant density case). More precisely, it is shown that the transition occurs for heavy vortices when the density ratio reaches a critical value, ${s}_{c} \simeq 1. 08$. For light vortices ($s\lt 1$) no transition was found. It is also shown that the first azimuthal mode that transits have an azimuthal wavenumber $m= \ensuremath{-} 2$ and the transition occurs for a swirl number (a measure of the azimuthal to axial velocity ratio), $q= 0. 57$. It is followed by $m= \ensuremath{-} 1$, then by $m= \ensuremath{-} 3$. When nonlinearities are allowed, it is found that they saturate the amplitude within the linear-response wavepacket, leaving the wavepacket fronts unaffected. The conclusions should thus be the same as those obtained in the linear case: the linear convective/absolute transition should coincide with the nonlinear one for the variable-density Batchelor vortex.

scholarly journals Flapping Instability of an Atomized Liquid Jet

2010 ◽  
Author(s):  
Jean-Philippe Matas ◽  
Alain Cartellier
Keyword(s):  
Experimental Study ◽  
Large Amplitude ◽  
Liquid Velocity ◽  
Velocity Ratio ◽  
Liquid Jet ◽  
Liquid Droplets ◽  
Typical Size ◽  
Coaxial Jets ◽  
Break Up ◽  
Large Wavelength

We present an experimental study of the flapping instability which appears when a coaxial liquid jet is atomized by a cocurrent fast gas stream. When primary atomization does not lead to a total break-up of the liquid jet, it undergoes a large-wavelength instability, characterized by very large amplitude oscillations, and can break into large liquid fragments whose typical size is the jet diameter. These large liquid fragments, and consequently the flapping instability, are to be avoided in applications related to combustion where liquid droplets need to be as small as possible. We carried out experiments with air and water coaxial jets, with a gas/liquid velocity ratio of order 50. We studied the consequence of the flapping instability on the break-up of the liquid jet. Measurements of the frequency of the instability were carried out. We suggest a mechanism where the flapping instability could be triggered by non axisymmetrical KH modes.

Empirical Correlation of the Primary Stability Variable of Liquid Jet and Liquid Sheet Under Acoustic Field

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
V. Sivadas ◽  
K. Balaji ◽  
M. Sampathkumar ◽  
M. M. Hassan ◽  
K. M. Karthik ◽  
...  
Keyword(s):  
Weber Number ◽  
Liquid Velocity ◽  
Primary Stability ◽  
Surface Tension Force ◽  
Liquid Sheet ◽  
Acoustic Energy ◽  
Inertia Force ◽  
Liquid Jet ◽  
Pipe Length ◽  
Stability Functions

The investigation focuses on optimizing the length of wind-pipe that transmits acoustic energy from the compression driver to the cavity of twin-fluid atomizers. To accomplish this objective, the primary variable of stability, that is, the breakup length of liquid jet and sheet under acoustic perturbations has been experimentally characterized for a range of wind-pipe length and liquid velocity. The analysis considers liquid phase Weber number in the range of 0.7–8, and the results are compared with primary breakup data without acoustic perturbations. The range of Weber number tested belongs to Rayleigh breakup zone, so that inertia force is negligible compared to surface tension force. It shows the existence of unique stability functions based on dimensionless products up to an optimum wind-pipe length, which extends greater for liquid sheet configuration. The present results may find relevance in atomizer design that utilizes acoustic source to enhance liquid column breakup processes.

scholarly journals Compressive behaviours of octet-truss lattices

2020 ◽  
Vol 234 (16) ◽  
pp. 3257-3269 ◽  
Author(s):  
Yifan Li ◽  
Huaiyuan Gu ◽  
Martyn Pavier ◽  
Harry Coules
Keyword(s):  
Failure Modes ◽  
Density Ratio ◽  
Three Dimensional ◽  
Compressive Load ◽  
High Strength ◽  
Detailed Comparison ◽  
Compressive Response ◽  
Beam Elements ◽  
Structural Applications ◽  
Octet Truss

Octet-truss lattice structures can be used for lightweight structural applications due to their high strength-to-density ratio. In this research, octet-truss lattice specimens were fabricated by stereolithography additive manufacturing with a photopolymer resin. The mechanical properties of this structure have been examined in three orthogonal orientations under the compressive load. Detailed comparison and description were carried out on deformation mechanisms and failure modes in different lattice orientations. Finite element models using both beam elements and three-dimensional solid elements were used to simulate the compressive response of this structure. Both the load reaction and collapse modes obtained in simulations were compared with test results. Our results indicate that three-dimensional continuum element models are required to accurately capture the behaviour of real trusses, taking into account the effects of finite-sized beams and joints.

Wake Flow of Single and Multiple Yawed Cylinders

2004 ◽  
Vol 126 (5) ◽  
pp. 861-870 ◽  
Author(s):  
A. Thakur ◽  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Side Wall ◽  
Wake Flow ◽  
Upstream Region ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Dimensional Approximation ◽  
The Face ◽  
Drag And Lift

An experimental and computational study is performed of the wake flow behind a single yawed cylinder and a pair of parallel yawed cylinders placed in tandem. The experiments are performed for a yawed cylinder and a pair of yawed cylinders towed in a tank. Laser-induced fluorescence is used for flow visualization and particle-image velocimetry is used for quantitative velocity and vorticity measurement. Computations are performed using a second-order accurate block-structured finite-volume method with periodic boundary conditions along the cylinder axis. Results are applied to assess the applicability of a quasi-two-dimensional approximation, which assumes that the flow field is the same for any slice of the flow over the cylinder cross section. For a single cylinder, it is found that the cylinder wake vortices approach a quasi-two-dimensional state away from the cylinder upstream end for all cases examined (in which the cylinder yaw angle covers the range 0⩽ϕ⩽60°). Within the upstream region, the vortex orientation is found to be influenced by the tank side-wall boundary condition relative to the cylinder. For the case of two parallel yawed cylinders, vortices shed from the upstream cylinder are found to remain nearly quasi-two-dimensional as they are advected back and reach within about a cylinder diameter from the face of the downstream cylinder. As the vortices advect closer to the cylinder, the vortex cores become highly deformed and wrap around the downstream cylinder face. Three-dimensional perturbations of the upstream vortices are amplified as the vortices impact upon the downstream cylinder, such that during the final stages of vortex impact the quasi-two-dimensional nature of the flow breaks down and the vorticity field for the impacting vortices acquire significant three-dimensional perturbations. Quasi-two-dimensional and fully three-dimensional computational results are compared to assess the accuracy of the quasi-two-dimensional approximation in prediction of drag and lift coefficients of the cylinders.

Influencing analysis of different baffle factors on oil liquid sloshing in automobile fuel tank

2020 ◽  
Vol 234 (13) ◽  
pp. 3180-3193
Author(s):  
Enhui Zhang ◽  
Wenyan Zhu ◽  
Lihe Wang
Keyword(s):  
Three Dimensional ◽  
Fuel Tank ◽  
Liquid Sloshing ◽  
Inertia Force ◽  
Dimensional Finite Element ◽  
Combined Action ◽  
Adverse Influence ◽  
Three Dimensional Finite Element ◽  
Influence Degree ◽  
Sloshing Pressure

Oil liquid sloshing is a common phenomenon in automobile fuel tank under variable working conditions. Installing baffles in automobile fuel tank is the most effective way to suppress adverse influence caused by oil liquid sloshing. Different types of three-dimensional finite element models filling oil liquid are created, meshed, and simulated. The reliability of simulation results is verified by test. The concept of time–area value is proposed in this work. In order to explore the influence of different baffle factors on oil liquid sloshing, six factors are studied. Six kinds of influencing factors are height, structure, shape, spacing, number, and placement of baffles. The sloshing pressure and time–area value are the core parameters for evaluating the influence degree. Some results could be obtained by comparing the parameters of oil liquid sloshing under the same condition. High baffles and baffles with small spacing have obvious attenuation influence on the pressure of oil liquid sloshing. Low baffles, double baffles, parallel baffles, and the combined action of inertia force and gravity are more beneficial to the reduction of time–area value. Time–area value is the largest and the smallest in fuel tank with intersection baffles and low baffles, respectively.

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