Symmetric and Asymmetric Disturbances in the Rayleigh Zone of an Air-Assisted Liquid Sheet: Theoretical and Experimental Analysis

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
V. Sivadas ◽  
S. Karthick ◽  
K. Balaji
Keyword(s):  
Growth Rate ◽  
Weber Number ◽  
High Speed ◽  
Low Frequency ◽  
Maximum Growth ◽  
Temporal Analysis ◽  
Average Frequency ◽  
Liquid Sheet ◽  
Number Ratio ◽  
Sheet Breakup

Abstract The temporal analysis of symmetric (dilatational) and asymmetric (sinusoidal) perturbations at the interface of a water sheet in a coflowing air stream focuses on low gas Weber number region (Weg < 0.4), namely, Rayleigh breakup zone. The motive for this investigation is to acquire a better insight of breakup phenomena involved, rather than technical relevance, by utilizing Kelvin–Helmholtz instability. Accordingly, perturbations are introduced on the basic flow whose stability is to be examined by the method of normal (Fourier) modes. The temporal growth-rate of perturbations is traced to extract the wavenumber associated with maximum growth-rate. Thus, the critical wavelength, in conjunction with the phase velocity of the disturbance will facilitate to obtain the corresponding breakup frequency of the liquid sheet. The analytical findings on liquid sheet breakup frequency with increasing Weber number ratio exhibit the dominance of symmetric wave over asymmetric wave. It also shows independent evolution of breakup frequency with respect to Weber number ratio for the respective perturbation modes, which appears to be a pointed profile. That is, the frequency contour for dilatational mode dips, whereas it rises for the sinusoidal mode and at the Weber number ratio of 0.518 the crossover occur. The theoretical results were substantiated by high-speed flow visualization studies that discern the coexistence of low-frequency (primary) and high-frequency (intermediate) breakup events. Furthermore, the empirical average frequency data track reasonably well with the dilatational instability.

Instability of a Moving Cylindrical Liquid Sheet

1985 ◽  
Vol 107 (4) ◽  
pp. 451-454 ◽  
Author(s):  
G. Biswas ◽  
S. K. Som ◽  
A. S. Gupta
Keyword(s):  
Growth Rate ◽  
Weber Number ◽  
Finite Thickness ◽  
Sheet Thickness ◽  
Maximum Growth ◽  
Liquid Sheet ◽  
Maximum Growth Rate ◽  
Capillary Instability ◽  
Uniform Velocity ◽  
Outer Circumference

The instability of a cylindrical liquid sheet of finite thickness moving with a uniform velocity in still air is studied theoretically with the aim of throwing light on the break-up of films during atomization. It is shown that instability occurs for an axisymmetric disturbance when its wavelength exceeds the outer circumference of the sheet. For small values of the Weber number W(= T/ρaU2ra) a sheet of given thickness tends to become unstable for disturbances of large wavelengths although it is completely stabilized when W < 2.5 (approx.). The maximum growth rate for instability increases with W for fixed value of the sheet thickness. For fixed W, it is found that λ¯m (the wavelength corresponding to maximum growth rate) increases rather slowly with increase in the sheet thickness. The value of λ¯m decays rapidly from a high value as Weber number increases for a fixed sheet thickness. Further as W → ∞, λ¯m approaches asymptotically the value 10 (approx.) which agrees with the corresponding value due to Rayleigh in his study of the capillary instability of a jet.

Dynamics of Liquid Sheet Breakup in Splash Plate Atomization

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
G. Thunivumani ◽  
Hrishikesh Gadgil
Keyword(s):  
Solid Surface ◽  
Weber Number ◽  
Jet Impingement ◽  
Liquid Sheet ◽  
Force Balance ◽  
Impingement Angle ◽  
Wide Range ◽  
Perforated Sheet ◽  
Sheet Breakup ◽  
Regime Map

An experimental study was conducted to investigate the breakup of a liquid sheet produced by oblique impingement of a liquid jet on a plane solid surface. Experiments are carried out over a wide range of jet Weber number (80–6300) and various jet impingement angles (30 deg, 45 deg, and 60 deg) are employed to study the sheet dynamics. The breakup of a liquid sheet takes place in three modes, closed rim, open rim, and perforated sheet, depending upon the Weber number. The transitions across the modes are also influenced by the impingement angle with the transition Weber number reducing with increase in impingement angle. A modified regime map is proposed to illustrate the role of impingement angle in breakup transitions. A theoretical model based on force balance at the sheet edge is developed to predict the sheet parameters by taking the shear interaction between the sheet and the solid surface into account. The sheet shape predicted by the model fairly matches with the experimentally measured sheet shape. The breakup length and width of the sheet are measured and comparisons with the model predictions show good agreement in closed rim mode of breakup.

scholarly journals Auroral kilometric radiation from a nonstationary thin plasma cavity

2012 ◽  
Vol 30 (7) ◽  
pp. 1093-1097 ◽  
Author(s):  
T. M. Burinskaya ◽  
J.-L. Rauch
Keyword(s):  
Growth Rate ◽  
Low Frequency ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Auroral Kilometric Radiation ◽  
Plasma Motion ◽  
Frequency Plasma ◽  
Waveguide Model ◽  
Thin Plasma

Abstract. Results obtained using a waveguide model of the AKR generation in thin plasma cavities are presented. Taking into account the occurrence of low frequency plasma motion in the regions of the AKR generation, we have considered a wave escape from a thin plasma cavity with adiabatically slowly varying width, and show that there can exist localized regions of instability from which the extraordinary X-mode waves, growing in time, can be radiated outwards. It has been found that waves, propagating quasi-tangentially to the source frontiers, have the maximum growth rate and escape outward most efficiently, which is in accordance with experimental observations.

A non-linear model for impinging jets atomization

2008 ◽  
Vol 222 (2) ◽  
pp. 213-224 ◽  
Author(s):  
E A Ibrahim ◽  
B E Outland
Keyword(s):  
Linear Model ◽  
Weber Number ◽  
Drop Size ◽  
Impinging Jets ◽  
Liquid Sheet ◽  
Linear Perturbation ◽  
Breakup Length ◽  
Half Wavelength ◽  
Non Linear ◽  
Sheet Breakup

The problem considered is predicting the characteristics of the spray produced by atomization of an attenuating liquid sheet formed by the impingement of two liquid jets of equal diameters and momenta. A second-order non-linear perturbation analysis is employed to model the evolution of harmonic instability waves that lead to sheet distortion and fragmentation. The onset of atomization occurs when the uneven surface modulations of the thinning sheet bring its upper and lower interfaces in contact. It is found that the sheet is torn into ligaments at each half wavelength. The instability of the ligaments causes their eventual disintegration into drops. The results indicate that sheet breakup length, time, and resultant drop size decrease as Weber number is increased. A higher Weber number induces a greater sheet breakup thickness. The breakup length, thickness, time, and drop size are diminished at larger impingement angles. The theoretical predictions of the present non-linear model are in good agreement with available experimental data and empirical correlations for sheet breakup length and drop size.

Developing Technologies of SiC Gas Source Growth Method

2016 ◽  
Vol 858 ◽  
pp. 23-28 ◽  
Author(s):  
Jun Kojima ◽  
Yuichiro Tokuda ◽  
Emi Makino ◽  
Naohiro Sugiyama ◽  
Norihiro Hoshino ◽  
...  
Keyword(s):  
Growth Rate ◽  
Mass Production ◽  
High Speed ◽  
High Growth ◽  
Maximum Growth ◽  
High Growth Rate ◽  
Average Growth ◽  
Gas Source ◽  
Growth Method ◽  
Production Technologies

In order to diffuse the use of SiC, mass-production technologies of SiC wafers are needed. It is easy to be understood that high-speed and long-sized growth technologies are connected directly with mass-production technologies. The gas source growth method such as HT-CVD has the possibilities and the potential of the high-speed and long-sized growth. In this article, it was clarified that the high growth rate were achieved by the control of the source gas partial pressures and by the gas boundary layers. The average growth rate was 1mm/h on the f4 inch-diameter crystal, and the maximum growth rate reached 3.6 mm/h on the 12.5x25 mm tetragon by the above gas control. The crystal qualities of the gas source methods were also evaluated the equivalent level in comparison with the sublimation method. Concerning the 1mm/h-growth f3 inch crystal, the densities of TSDs were kept in the 102 cm-2 levels from the seed to the upper-side of the ingot. Moreover, the ingot size increased year by year and a f4 inch x 43 mm sized ingot has been developed.

A Functional Correlation for the Primary Breakup Processes of Liquid Sheets Emerging From Air-Assist Atomizers

2006 ◽  
Vol 129 (2) ◽  
pp. 188-193 ◽  
Author(s):  
V. Sivadas ◽  
M. V. Heitor ◽  
Rui Fernandes
Keyword(s):  
High Speed ◽  
Imaging Techniques ◽  
Flux Ratio ◽  
Liquid Sheet ◽  
Spray Angle ◽  
High Speed Imaging ◽  
Liquid Sheets ◽  
Primary Breakup ◽  
Sheet Breakup ◽  
The Stability

The study aims to highlight a general relationship between the characteristic variables of liquid sheet breakup and the principal forces of the flow domain. To accomplish this objective, an experimental investigation on air-assisted liquid sheets was carried out for a range of liquid-to-air velocities. The associated spray angle, breakup frequency, and breakup length were measured by exploiting high-speed imaging techniques. The results demonstrate that, when the stability variables are related to the liquid–air momentum flux ratio, a high correlation was attained for a range of flow conditions where capillary instability is insignificant.

Effect of Weber Number on Disintegration of Liquid Sheet With Co-Flowing Gas

2014 ◽  
Author(s):  
Mohammad Ali ◽  
Mohammed S. Mayeed ◽  
A. K. M. Sadrul Islam ◽  
M. Quamrul Islam
Keyword(s):  
Weber Number ◽  
Gaseous Medium ◽  
Normal Force ◽  
Surface Force ◽  
Liquid Sheet ◽  
Navier Stokes ◽  
Stokes Systems ◽  
Sheet Breakup ◽  
Surface Tension Forces ◽  
Moving Liquid

The disturbances on the surface of a moving liquid sheet in a moving gaseous medium are studied to analyze the dynamics and breakup of the liquid sheet with co-flowing gas. The problem, composed of the Navier-Stokes systems associated with surface tension forces, is solved by the Volume of Fluid (VOF) technique with a Continuum Surface Force (CSF) manner artificially smoothing the discontinuity present at the interface. The investigation provides the insights into the dynamics and breakup processes. The inlet velocities of liquid and gas are determined by liquid and gas Weber number, respectively. It is found that the disturbances occurred by the gas Weber number controls the instability process for the liquid sheet breakup. The results show that there is a range of gas Weber number for the occurrence of droplet. In this range, the gas Weber number causes an aerodynamic normal force at the tip of the liquid sheet which is able to form a droplet from the tip of the liquid sheet. Below that range of gas Weber number, the aerodynamic normal force at the tip of the sheet is too low to produce a droplet and above the range, the aerodynamic normal force stretches the liquid sheet too much and no droplet occurs.

Wind Speed Dependency of Low-Frequency Vibration Levels in Full-Scale Wind Turbines

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Xavier Escaler ◽  
Toufik Mebarki
Keyword(s):  
Wind Speed ◽  
Wind Turbines ◽  
High Speed ◽  
Wind Farm ◽  
Low Frequency ◽  
Average Frequency ◽  
Operating Conditions ◽  
Positive Slope ◽  
Low Frequency Vibration ◽  
Linear Fit

A series of continuous vibration measurements in 14 upwind wind turbines of the same model and belonging to the same wind farm have been conducted. The data were acquired over a period lasting approximately half a year. The tower axial vibration acceleration has been monitored in the frequency band from 0 to 10 Hz with an accelerometer mounted on the gearbox casing between the intermediate and the high-speed shafts. It has been observed that the average frequency spectrum is dominated by the blade passing frequency in all the wind turbines. The evolution of the vibration magnitudes over the entire range of operating conditions is also very similar for all the wind turbines. The root-mean-square (rms) acceleration value has been correlated with the wind speed, and it has been found that a linear fit with a positive slope is a useful model for prediction purposes.

High-Speed Growth of High-Quality 4H-SiC Bulk by Solution Growth Using Si-Cr Based Melt

2010 ◽  
Vol 645-648 ◽  
pp. 13-16 ◽  
Author(s):  
Katsunori Danno ◽  
Hiroaki Saitoh ◽  
Akinori Seki ◽  
H. Daikoku ◽  
Y. Fujiwara ◽  
...  
Keyword(s):  
Growth Rate ◽  
High Speed ◽  
Grown Crystal ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Solution Growth ◽  
X Ray Diffraction ◽  
Large Crystal ◽  
X Ray ◽  
Basal Plane Dislocation

High-speed solution growth using Si-Cr based melt has been performed on on-axis 4H-SiC(0001) at a high temperature of about 2000°C. The maximum growth rate for one-hour growth reaches to 1120 m/h, while the typical growth rate of growth for 2h is about 500 m/h. A large crystal that is about 25 mm in diameter and 1650 m in thickness can be obtained by growth for 5h. The crystal quality is confirmed to be homogeneous by X-ray diffraction and X-ray topography, because FWHM is less than 30 arcsec. Etch pit density of the threading dislocations in the grown crystal is 103-104 cm-2, and that of basal plane dislocation is 2×102-3×103 cm-2. Resistivity of the crystals grown by the solution growth is comparable to those of crystals grown by physical vapor transport technique.

Influence of a Scarfed Portal on the Compression Wave Generated by a High-Speed Train Entering a Tunnel

2005 ◽  
Vol 24 (4) ◽  
pp. 203-217 ◽  
Author(s):  
A. Winslow ◽  
M. S. Howe ◽  
M. Iida
Keyword(s):  
Growth Rate ◽  
Compression Wave ◽  
High Speed ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
High Speed Train ◽  
Wave Characteristics ◽  
Additional Improvement ◽  
Side Walls ◽  
Tunnel Entrance

An optimally designed entrance portal must be capable of minimizing the maximum growth rate of the compression wave generated when a high-speed train enters a tunnel. A theoretical and experimental investigation has been made to determine the changes in compression wave characteristics produced when the portal is ‘scarfed’ with tapering side walls. It is concluded that portal modifications of this type are unlikely to produce a significant reduction in the maximum compression wave growth rate. Small decreases in growth rate are possible (up to about 15%) for scarf walls extending a distance beyond the tunnel entrance of the order of the tunnel height, but little or no additional improvement is achieved with longer walls.

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