Stability of an annular power-law liquid sheet

2014 ◽  
Vol 229 (15) ◽  
pp. 2750-2759 ◽  
Author(s):  
Lijun Yang ◽  
Minglong Du ◽  
Qingfei Fu
Keyword(s):  
Stability Analysis ◽  
Power Law ◽  
Temporal Stability ◽  
Sheet Thickness ◽  
Momentum Equation ◽  
Liquid Sheet ◽  
Rheological Parameters ◽  
Stream Velocity ◽  
Gas Streams ◽  
Outer Interface

Because of the mathematical difficulties dealing with the nonlinear viscous stress term in momentum equation for power-law liquid, the study of stability analysis of a power-law liquid sheet has been lacking. In the present study, a temporal stability analysis has been carried out for an annular power-law liquid sheet exposed to both inner and outer-gas streams, by integrating the governing equations for the power-law liquid sheet. The dimensionless dispersion equation that governs the instability of liquid sheet is obtained by considering the velocity profile of liquid sheet. It is found that the instability of liquid sheet can be enhanced by independently increasing either the outer gas stream velocity, or the inner gas stream velocity. The liquid sheet is more unstable when both inner and outer gas streams are applied. To promote the instability of annular liquid sheet, a gas stream applied to the outer interface is more effective than when applied to the inner surface. The effects of rheological parameters on the instability of the liquid sheet are actually determined by the relative velocity across the gas–liquid interfaces. The surface tension, liquid sheet thickness, and outer surface radius of annular liquid sheet have been tested for their influence on the instability of annular power-law liquid sheet.

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.

Spray Characteristics of Elliptical Power-Law Fluid-Impinging Jets

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Fei Zhao ◽  
Li-Zi Qin ◽  
Qing-Fei Fu ◽  
Chao-Jie Mo ◽  
Li-Jun Yang
Keyword(s):  
Power Law ◽  
Impinging Jets ◽  
Liquid Sheet ◽  
Rheological Parameters ◽  
Power Law Fluid ◽  
Spray Characteristics ◽  
Theoretical Predictions ◽  
Fluid Jets ◽  
Atomization Efficiency ◽  
Improved Model

The spray characteristics of a liquid sheet contribute much to the investigation of atomization efficiency. Considering the jet contracting effect of elliptical jets, an improved model of elliptical power-law fluid jets is proposed herein to derive the spray characteristics. Some experiments have been conducted to verify its feasibility, and the results show a good agreement with theoretical predictions. The effect of the aspect ratio on sheet shape and thickness has been studied to interpret the phenomenon that liquid sheets formed by the impinging elliptical jets are more likely to disintegrate. The relationships between rheological parameters (K and n) and the spray features are also discussed.

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.

scholarly journals Instability of a liquid sheet with viscosity contrast in inertial microfluidics

2021 ◽  
Vol 44 (11) ◽  
Author(s):  
Kuntal Patel ◽  
Holger Stark
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Sheet Thickness ◽  
Liquid Sheet ◽  
Interfacial Instability ◽  
Parameter Study ◽  
Inertial Microfluidics ◽  
Inertial Focusing ◽  
Layer Flow

Abstract Flows at moderate Reynolds numbers in inertial microfluidics enable high throughput and inertial focusing of particles and cells with relevance in biomedical applications. In the present work, we consider a viscosity-stratified three-layer flow in the inertial regime. We investigate the interfacial instability of a liquid sheet surrounded by a density-matched but more viscous fluid in a channel flow. We use linear stability analysis based on the Orr–Sommerfeld equation and direct numerical simulations with the lattice Boltzmann method (LBM) to perform an extensive parameter study. Our aim is to contribute to a controlled droplet production in inertial microfluidics. In the first part, on the linear stability analysis we show that the growth rate of the fastest growing mode $$\xi ^{*}$$ ξ ∗ increases with the Reynolds number $$\text {Re}$$ Re and that its wavelength $$\lambda ^{*}$$ λ ∗ is always smaller than the channel width w for sufficiently small interfacial tension $$\Gamma $$ Γ . For thin sheets we find the scaling relation $$\xi ^{*} \propto mt^{2.5}_{s}$$ ξ ∗ ∝ m t s 2.5 , where m is viscosity ratio and $$t_{s}$$ t s the sheet thickness. In contrast, for thicker sheets $$\xi ^{*}$$ ξ ∗ decreases with increasing $$t_s$$ t s or m due to the nearby channel walls. Examining the eigenvalue spectra, we identify Yih modes at the interface. In the second part on the LBM simulations, the thin liquid sheet develops two distinct dynamic states: waves traveling along the interface and breakup into droplets with bullet shape. For smaller flow rates and larger sheet thicknesses, we also observe ligament formation and the sheet eventually evolves irregularly. Our work gives some indication how droplet formation can be controlled with a suitable parameter set $$\{\lambda ,t_{s},m,\Gamma ,\text {Re}\}$$ { λ , t s , m , Γ , Re } . Graphical Abstract

DUAL-MODE LINEAR ANALYSIS OF TEMPORAL INSTABILITY FOR POWER-LAW LIQUID SHEET

2016 ◽  
Vol 26 (4) ◽  
pp. 319-347 ◽  
Author(s):  
Han-Yu Deng ◽  
Feng Feng ◽  
Xiao-Song Wu
Keyword(s):  
Power Law ◽  
Linear Analysis ◽  
Liquid Sheet ◽  
Dual Mode ◽  
Temporal Instability

Thermorheological Characterization of Elastoviscoplastic Carbopol Ultrez 20 Gel

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
M. A. Hassan ◽  
Manabendra Pathak ◽  
Mohd. Kaleem Khan
Keyword(s):  
Experimental Investigation ◽  
Yield Stress ◽  
Elastic Properties ◽  
Viscous Dissipation ◽  
Power Law ◽  
Effect Of Temperature ◽  
Rheological Parameters ◽  
Frequency Range ◽  
Power Law Index

The temperature and concentration play an important role on rheological parameters of the gel. In this work, an experimental investigation of thermorheological properties of aqueous gel Carbopol Ultrez 20 for various concentrations and temperatures has been presented. Both controlled stress ramps and controlled stress oscillatory sweeps were performed for obtaining the rheological data to find out the effect of temperature and concentration. The hysteresis or thixotropic seemed to have negligible effect. Yield stress, consistency factor, and power law index were found to vary with temperature as well as concentration. With gel concentration, the elastic effect was found to increase whereas viscous dissipation effect was found to decrease. Further, the change in elastic properties was insignificant with temperature in higher frequency range of oscillatory stress sweeps.

Spatial Stability Analysis of a Flap Side Edge Vortex

2005 ◽  
Vol 4 (1-2) ◽  
pp. 37-47
Author(s):  
Jean-Philippe Brazier ◽  
Frédéric Moens ◽  
Philippe Bardoux
Keyword(s):  
Stability Analysis ◽  
Temporal Stability ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Navier Stokes ◽  
Mean Flow ◽  
Side Edge ◽  
Amplification Rate ◽  
Edge Vortex ◽  
Flap Deflection

The flap side edge vortex is suspected to contribute to aerodynamic noise generation. Using a temporal stability analysis, Khorrami and Singer have shown that unstable modes could exist in this vortex. Due to the convective nature of this instability, a spatial analysis is more suitable. This is the subject of the present work. The mean flow past a 2D wing with a half-span flap has been computed with a steady 3D Navier-Stokes code. Then, local linear stability calculations are performed in several planes perpendicular to the vortex axis. The vortex is assumed axisymmetric and modelled with Batchelor's analytical vortex. Using Gaster's relation, the spatial amplification rate is calculated, giving by integration the relative amplitude of the fluctuations. Some low-frequency fluctuations are seen to be preferentially amplified by the vortex, but the amplifications remain small, so that this mechanism alone should not produce important noise in this particular configuration, where the flap deflection angle is moderate.

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