scholarly journals Liquid sheet thickness measurements using multi-pass, time-gated femtosecond imaging

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Dilip Sanadi ◽  
Saïd Idlahcen ◽  
Jean-Bernard Blaisot ◽  
Fabien Thiesset
Keyword(s):  
Sheet Thickness ◽  
Liquid Sheet ◽  
Thickness Measurements

Linear stability analysis of an electrified incompressible liquid sheet streaming into a compressible ambient gas

2016 ◽  
Vol 231 (10) ◽  
pp. 1849-1858 ◽  
Author(s):  
Yuxin Liu ◽  
Chaojie Mo ◽  
Lujia Liu ◽  
Qingfei Fu ◽  
Lijun Yang
Keyword(s):  
Stability Analysis ◽  
Electric Field ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Density Ratio ◽  
Sheet Thickness ◽  
Liquid Sheet ◽  
Wave Number ◽  
Liquid Density ◽  
Ambient Gas

This article presents the linear stability analysis of an electrified liquid sheet injected into a compressible ambient gas in the presence of a transverse electric field. The disturbance wave growth rates of sinuous and varicose modes were determined by solving the dispersion relation of the electrified liquid sheet. It was determined that by increasing the Mach number of the ambient gas from subsonic to transonic, the maximum growth rate and the dominant wave number of the disturbances were increased, and the increase was greater in the presence of the electric field. The electrified liquid sheet was more unstable than the non-electrified sheet. The increase of both the gas-to-liquid density ratio and the electrical Euler number accelerated the breakup of the liquid sheet for both modes; while the ratio of distance between the horizontal electrode and the liquid-sheet-to-sheet thickness had the opposite effect. High Reynolds and Weber numbers accelerated the breakup of the electrified liquid sheet.

Instability of a spatially developing liquid sheet

1997 ◽  
Vol 331 ◽  
pp. 127-144 ◽  
Author(s):  
LUIGI DE LUCA ◽  
MICHELA COSTA
Keyword(s):  
Flow Rate ◽  
Weber Number ◽  
Order Approximation ◽  
Unit Length ◽  
Sheet Thickness ◽  
Vertical Direction ◽  
Multiple Scale ◽  
Liquid Sheet ◽  
Nonlinear Phenomena ◽  
Local Character

The linear stability of an inviscid two-dimensional liquid sheet falling under gravity in a still gas is studied by analysing the asymptotic behaviour of a localized perturbation (wave-packet solution to the initial value problem). Unlike previous papers the effect of gravity is fully taken into account by introducing a slow length scale which allows the flow to be considered slightly non-parallel. A multiple-scale approach is developed and the dispersion relations for both the sinuous and varicose disturbances are obtained to the zeroth-order approximation. These exhibit a local character as they involve a local Weber number Weη. For sinuous disturbances a critical Weη equal to unity is found below which the sheet is locally absolutely unstable (with algebraic growth of disturbances) and above which it is locally convectively unstable. The transition from absolute to convective instability occurs at a critical location along the vertical direction where the flow Weber number equals the dimensionless sheet thickness. This critical distance, as measured from the nozzle exit section, increases with decreasing the flow Weber number, and hence, for instance, the liquid flow rate per unit length. If the region of absolute instability is relatively small it may be argued that the system behaves as a globally stable one. Beyond a critical size the flow receptivity is enhanced and self-sustained unstable global modes should arise. This agrees with the experimental evidence that the sheet breaks up as the flow rate is reduced. It is conjectured that liquid viscosity may act to remove the algebraic growth, but the time after which this occurs could be not sufficient to avoid possible nonlinear phenomena appearing and breaking up the sheet.

Detailed Numerical Simulation of Two Impinging Jets With Moderate Injection Velocities

2019 ◽  
Author(s):  
Yue Ling ◽  
Weixiao Shang ◽  
Jun Chen
Keyword(s):  
Thickness Distribution ◽  
Sheet Thickness ◽  
Impinging Jets ◽  
Liquid Sheet ◽  
Liquid Jets ◽  
Rocket Engines ◽  
Flow Solver ◽  
Plane Normal ◽  
Jet Injectors ◽  
Propellant Rocket

Abstract Impinging-jet injectors are commonly used in liquid propellant rocket engines. Two cylindrical liquid jets impinge at a certain angle and form a liquid sheet in the plane normal to the jets. When the Reynolds and Weber numbers are large, the liquid sheet becomes unstable and disintegrates into liquid ligaments and droplets. In the present study, we focus on cases with moderate injection velocities so that the liquid sheet remains unbroken. Detailed numerical simulations are performed using the adaptive multiphase flow solver, Basilisk. The volume-of-fluid method is used to resolve the gas-liquid interface. Grid-refinement studies are conducted to verify the formation of the liquid sheet is accurately captured in simulation. The numerical results are compared to the recent experimental measurement of the sheet thickness distribution by partial coherent interferometry and a good agreement is achieved.

Absolute and convective instability of a liquid sheet

1990 ◽  
Vol 220 ◽  
pp. 673-689 ◽  
Author(s):  
S. P. Lin ◽  
Z. W. Lian ◽  
B. J. Creighton
Keyword(s):  
Weber Number ◽  
Convective Instability ◽  
Density Ratio ◽  
Sheet Thickness ◽  
Surface Tension Force ◽  
Liquid Sheet ◽  
Inertia Force ◽  
Liquid Density ◽  
Gas To Liquid ◽  
Density Ratios

The linear stability of a viscous liquid sheet in the presence of ambient gas is investigated. It is shown that there are two independent modes of instability, sinuous and varicose. The large-time asymptotic amplitude of sinuous disturbances is found to be bounded but non-vanishing for all calculated values of Reynolds numbers and the gas-to-liquid density ratios when the Weber number is greater than one half. The Weber numberWeis defined as the ratio of the surface tension force to the inertia force per unit area of the gas–liquid interface. WhenWeis smaller than one half, the sinuous mode is stable if the gas-to-liquid density ratio is zero, otherwise it is convectively unstable. The varicose mode is always convectively unstable unless the density ratio,Q, is zero. Then it is asymptotically stable. The spatial growth rate of the varicose mode is smaller than that of the sinuous mode for the same flow parameters. The wavelength of the most amplified waves in both modes is found to scale with the product of the sheet thickness andQ/We. It is shown, by use of the energy equation, that the mechanism of instability is a capillary rupture whenWe[ges ] 0.5, and the convective instability is due to the interfacial pressure fluctuation whenWe< 0.5.

Instability of a Confined Viscoelastic Liquid Sheet in a Viscous Gas Medium

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Run-ze Duan ◽  
Zhi-ying Chen ◽  
Chen Wang ◽  
Li-jun Yang
Keyword(s):  
Flat Plate ◽  
Time Constant ◽  
Sheet Thickness ◽  
Liquid Sheet ◽  
Viscoelastic Liquid ◽  
Wave Number ◽  
Rheological Parameters ◽  
Viscous Gas ◽  
Liquid Sheets ◽  
Elasticity Number

A linear analysis method was used to investigate the instability behavior of a viscoelastic liquid sheet moving through a viscous gas bounded by two horizontal parallel flat plates. The liquid sheet velocity profile was taken into account. The result showed that the velocity gradient of viscoelastic liquid sheets was greater than that of the corresponding Newtonian sheets. The effects of time-constant, elasticity number, and the ratio of distance between the liquid sheet and flat plate to liquid sheet thickness on the velocity profiles of viscoelastic liquid sheets were also investigated. The relationship between temporal growth rate and the wave number was obtained using linear stability analysis and solved using the Chebyshev spectral collocation method. The rheological parameters and flow parameters were tested for their influence on the instability of the viscoelastic liquid sheets. It is concluded that disturbances grow faster on viscoelastic liquid sheets than on Newtonian sheets with identical zero shear viscosity. Increasing the momentum flux ratio, elasticity number, Weber number, and liquid Reynolds number accelerated the breakup of the viscoelastic liquid sheet, while increasing the time constant, ratio of the distance between the liquid sheet, and the flat plate to the liquid sheet thickness had the opposite effect.

Effects of orifice divergence on hollow cone spray at low injection pressures

2018 ◽  
Vol 233 (11) ◽  
pp. 4091-4105 ◽  
Author(s):  
Kushal Ghate ◽  
Thirumalachari Sundararajan
Keyword(s):  
Cone Angle ◽  
Sheet Thickness ◽  
Liquid Sheet ◽  
Divergence Angle ◽  
Sauter Mean Diameter ◽  
Spray Cone Angle ◽  
Spray Cone ◽  
Air Core ◽  
Mean Diameter ◽  
Injection Pressures

In this work, the effects of orifice divergence on spray characteristics have been reported. Parameters such as spray cone angle, liquid sheet thickness, coefficient of discharge, break-up length, and Sauter mean diameter are greatly affected by the half divergence angle [Formula: see text] at orifice exit. An experimental investigation is carried out in which water sprays from five atomizers having half divergence angle values of 0°, 5°, 10°, 15°, and 20° are studied at different injection pressures. Image processing techniques are used to measure spray cone angle and break-up length from spray images, whereas the sheet thickness outside the orifice exit is obtained using the scattered light from a thin Nd-YAG Laser beam. Phase Doppler interferometry is also used to obtain the Sauter mean diameter at different axial locations. A few numerical simulations based on the volume of fluid method are included to obtain physical insight of the liquid film development and air core flow inside the atomizer. It is observed that the liquid sheet thickness as well as tangential and radial components of velocity at orifice exit are modified drastically with a change in half divergence angle. As a consequence, the droplet size distribution is also altered by variation in the nozzle divergence angle. The mechanism responsible for such variations in the spray behavior is identified as the formation of an air core or air cone inside the liquid injector as a result of the swirl imparted to the liquid flow.

scholarly journals Energy Considerations in Twin-Fluid Atomization

1990 ◽  
Author(s):  
Arthur H. Lefebvre
Keyword(s):  
Drop Size ◽  
Sheet Thickness ◽  
Ambient Air ◽  
Liquid Sheet ◽  
Air Pressure ◽  
Air Velocity ◽  
Atomization Process ◽  
Flow Situation ◽  
Heating Oil ◽  
Main Factor

With certain types of prefilming airblast atomizers, the manner in which the atomizing air impinges on the liquid sheet prohibits the wave formation that normally precedes the breakup of a liquid sheet into drops. Instead, the liquid is shattered almost instantaneously into drops of various sizes. This prompt atomization process is characterized by a broad range of drop sizes in the spray and by a lack of sensitivity of mean drop size to variations in liquid viscosity, atomizing air pressure, and initial liquid sheet thickness. Evidence is presented to show that which of these two different modes of atomization will occur in any given flow situation is largely dependent on the angle at which the atomizing air impinges on the liquid sheet. An equation for mean drop size, derived from the assumption that the main factor controlling prompt atomization is the ratio of the energy required for atomization to the kinetic energy of the atomizing air, is shown to provide a good fit to experimental data acquired from atomization studies on water and heating oil, carried out over wide ranges of air velocity, air/liquid ratio, and ambient air pressure.

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