Unsteady critical liquid sheet flows

2017 ◽  
Vol 821 ◽  
pp. 219-247 ◽  
Author(s):  
M. Girfoglio ◽  
F. De Rosa ◽  
G. Coppola ◽  
L. de Luca
Keyword(s):  
Flow Velocity ◽  
Weber Number ◽  
Liquid Sheet ◽  
Global Dynamics ◽  
Equivalent Stiffness ◽  
Supercritical Regime ◽  
Local Flow ◽  
System Perspective ◽  
Linear Approach ◽  
Small Disturbances

The unsteady global dynamics of a gravitational liquid sheet interacting with a one-sided adjacent air enclosure (commonly referred to as nappe oscillation configuration) is addressed under the assumptions of potential flow and the presence of surface tension effects. From a theoretical viewpoint the problem is challenging, because from previous literature it is known that the equation governing the evolution of small disturbances exhibits a singularity at the vertical station where the local flow velocity equals the capillary wave velocity (local critical condition), although the solution to the problem has not yet been found. The equation governing the local dynamics resembles one featuring the forced vibrations of a string of finite length, formulated in the reference frame moving with the flow velocity, and exhibits both slow and fast characteristic curves. From the global system perspective the nappe behaves as a driven damped spring–mass oscillator, where the inertial effects are linked to the liquid sheet mass and the spring is represented by the equivalent stiffness of the air enclosure acting on the displacement of the compliant nappe centreline. A suited procedure is developed to remove the singularity of the integro-differential operator for Weber numbers less than unity. The investigation is carried out by means of a modal (i.e. time asymptotic) linear approach, which is corroborated by numerical simulations of the governing equation and supported by systematic comparisons with experimental data from the literature, available in the supercritical regime only. As regards the critical regime for the unit Weber number, the major theoretical result is a sharp increase in oscillation frequency as the flow Weber number is gradually reduced from supercritical to subcritical values due to the shift of the prevailing mode from the slow one to the fast one.

Nonlinear instability of plane liquid sheets

2000 ◽  
Vol 406 ◽  
pp. 281-308 ◽  
Author(s):  
SEYED A. JAZAYERI ◽  
XIANGUO LI
Keyword(s):  
Weber Number ◽  
Density Ratio ◽  
Perturbation Expansion ◽  
Liquid Sheet ◽  
Fundamental Wave ◽  
Liquid Density ◽  
Initial Amplitude ◽  
Nonlinear Stability Analysis ◽  
Liquid Sheets ◽  
Breakup Time

A nonlinear stability analysis has been carried out for plane liquid sheets moving in a gas medium at rest by a perturbation expansion technique with the initial amplitude of the disturbance as the perturbation parameter. The first, second and third order governing equations have been derived along with appropriate initial and boundary conditions which describe the characteristics of the fundamental, and the first and second harmonics. The results indicate that for an initially sinusoidal sinuous surface disturbance, the thinning and subsequent breakup of the liquid sheet is due to nonlinear effects with the generation of higher harmonics as well as feedback into the fundamental. In particular, the first harmonic of the fundamental sinuous mode is varicose, which causes the eventual breakup of the liquid sheet at the half-wavelength interval of the fundamental wave. The breakup time (or length) of the liquid sheet is calculated, and the effect of the various flow parameters is investigated. It is found that the breakup time (or length) is reduced by an increase in the initial amplitude of disturbance, the Weber number and the gas-to-liquid density ratio, and it becomes asymptotically insensitive to the variations of the Weber number and the density ratio when their values become very large. It is also found that the breakup time (or length) is a very weak function of the wavenumber unless it is close to the cut-off wavenumbers.

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.

Transience to instability in a liquid sheet

2010 ◽  
Vol 666 ◽  
pp. 358-390 ◽  
Author(s):  
N. S. BARLOW ◽  
B. T. HELENBROOK ◽  
S. P. LIN
Keyword(s):  
Asymptotic Stability ◽  
Weber Number ◽  
Convective Instability ◽  
Initial Conditions ◽  
Fourier Integral ◽  
Liquid Sheet ◽  
Series Solutions ◽  
Integral Response ◽  
Gaussian Perturbation ◽  
Ambient Gas

Series solutions are found which describe the evolution to absolute and convective instability in an inviscid liquid sheet flowing in a quiescent ambient gas and subject to a localized perturbation. These solutions are used to validate asymptotic stability predictions for sinuous and varicose disturbances. We show how recent disagreements in growth predictions stem from assumptions made when arriving at the Fourier integral response. Certain initial conditions eliminate or reduce the order of singularities in the Fourier integral. If a Gaussian perturbation is applied to both the position and velocity of a sheet when the Weber number is less than one, we observe absolutely unstable sinuous waves which grow liket1/3. If only the position is perturbed, we find that the sheet is stable and decays liket−2/3at the origin. Furthermore, if both the position and velocity of a sheet are perturbed in theabsenceof ambient gas, we observe a new phenomenon in which sinuous waves neither grow nor decay and varicose waves grow liket1/2with a convective instability.

High Resolution Particle Image Velocimetry and CH-PLIF Measurements and Analysis of a Shear Layer Stabilized Flame

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
C. W. Foley ◽  
I. Chterev ◽  
J. Seitzman ◽  
T. Lieuwen
Keyword(s):  
Particle Image Velocimetry ◽  
High Resolution ◽  
Shear Layer ◽  
Flow Velocity ◽  
Particle Image ◽  
Flame Stabilization ◽  
Flow Conditions ◽  
Local Flow ◽  
Image Velocimetry ◽  
Flow Velocities

Understanding the mechanisms and physics of flame stabilization and blowoff of premixed flames is critical toward the design of high velocity combustion devices. In the high bulk flow velocity situation typical of practical combustors, the flame anchors in shear layers where the local flow velocities are much lower. Within the shear layer, fluid strain deformation rates are very high and the flame can be subjected to significant stretch levels. The main goal of this work was to characterize the flow and stretch conditions that a premixed flame experiences in a practical combustor geometry and to compare these values to calculated extinction values. High resolution, simultaneous particle image velocimetry (PIV) and planar laser induced fluorescence of CH radicals (CH-PLIF) measurements are used to capture the flame edge and near-field stabilization region. When approaching lean limit extinction conditions, we note characteristic changes in the stretch and flow conditions experienced by the flame. Most notably, the flame becomes less critically stretched when fuel/air ratio is decreased. However, at these lean conditions, the flame is subject to higher mean flow velocities at the edge, suggesting less favorable flow conditions are present at the attachment point of the flame as blowoff is approached. These measurements suggest that blowoff of the flame from the shear layer is not directly stretch extinction induced, but rather the result of an imbalance between the speed of the flame edge and local tangential flow velocity.

Structural Analysis of Selected Failures Caused by the 27 February 2010 Chile Tsunami

2012 ◽  
Vol 28 (1_suppl1) ◽  
pp. 215-243 ◽  
Author(s):  
Ian Robertson ◽  
Gary Chock ◽  
Juan Morla
Keyword(s):  
Flow Velocity ◽  
Structural Performance ◽  
Structural Element ◽  
Local Flow ◽  
Inundation Depth ◽  
Hydrodynamic Loading ◽  
Tsunami Damage ◽  
Chile Earthquake ◽  
Chile Tsunami ◽  
Loading Estimates

Following the 2010 Chile earthquake and tsunami, the authors participated in the EERI reconnaissance team that traveled to Chile to document damage and structural performance. The authors focused on tsunami damage following the earthquake. A summary of tsunami damage to structures is given. Based on a series of well-defined structural element failures at sites where inundation depth was measured, the team was able to evaluate the hydrodynamic loading required to cause these failures and derive estimated lower bound flow velocity overland during the event. It was estimated that the velocity exceeded 3.2 m/s in Talcahuano harbor and 4.3 m/s in the coastal town of Dichato. When found in proximity to damaged buildings and other larger structures of interest, these simple structures can serve as “flow surrogate instruments” to estimate the local flow velocity. Failure analysis of these simple structures indicated that the hydrodynamic loading estimates provided by FEMA P646 may be unconservative.

Influence of the flow velocity on membrane-aerated biofilm reactors: Application of a rotating disk for local flow control

2020 ◽  
Vol 164 ◽  
pp. 107771
Author(s):  
Tadashi Shoji ◽  
Ryuya Itoh ◽  
Tadashi Nittami ◽  
Tatsuto Kageyama ◽  
Miyuki Noguchi ◽  
...  
Keyword(s):  
Flow Control ◽  
Flow Velocity ◽  
Rotating Disk ◽  
Local Flow ◽  
Biofilm Reactors

scholarly journals Hydraulic and Mechanical Impacts of Pore Space Alterations within a Sandstone Quantified by a Flow Velocity-Dependent Precipitation Approach

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3100 ◽  
Author(s):  
Maria Wetzel ◽  
Thomas Kempka ◽  
Michael Kühn
Keyword(s):  
Flow Velocity ◽  
Power Law ◽  
Elastic Moduli ◽  
Rock Properties ◽  
Local Flow ◽  
Mineral Growth ◽  
Macro Scale ◽  
Elastic Rock ◽  
The Impact ◽  
Flow Velocities

Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny–Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface.

Investigation on Velocity Distribution Around the Wrapping Wire in an Inner Subchannel of Fuel Pin Bundle

2012 ◽  
Author(s):  
Masahiro Nishimura ◽  
Hiroyuki Sato ◽  
Hideki Kamide ◽  
Hiroyuki Ohshima ◽  
Kazuyoshi Nagasawa ◽  
...  
Keyword(s):  
Refractive Index ◽  
Velocity Distribution ◽  
Flow Velocity ◽  
Fast Reactor ◽  
Horizontal Plane ◽  
Vertical Plane ◽  
Heat Removal ◽  
Water Model ◽  
Local Flow ◽  
Fuel Pin

A sodium cooled fast reactor is designed to attain a high burn-up core in commercialized fast reactor cycle systems. In high burn-up fuel subassemblies, deformation of fuel pin due to the swelling and thermal bowing may decrease local flow velocity via change of flow area in the subassembly and influence the heat removal capability. Therefore, it is important to obtain the flow velocity distribution in a wire wrapped pin bundle. In this study, water experiments were carried out to investigate the detailed velocity distribution in inner subchannel of the pin bundle geometry. These basic data are not only useful for understanding of pin bundle thermal hydraulics but also code validation. A wire-wrapped 3-pin bundle water model was applied to investigate the detailed velocity distribution in an inner subchannel surrounded by 3 pins with the wrapping wire. The test section consists of an irregular hexagonal acrylic duct tube and fluorinated resin pins which have nearly the same refractive index with that of water and a high light transmission rate. This refractive index matching enables to visualize the inner subchannel through the outer pins. The velocity distribution in the inner subchannel with the wrapping wire was measured by PIV (Particle Image Velocimetry) through two sides of the duct tube. Typical flow velocity conditions in the pin bundle were 1.6m/s (Re = 13,500) and 0.36m/s (Re = 2,700). Feature of stream regime in the subchannel existing wrapping wire was visualized in vertical and horizontal plane. The time averaged velocity field in the horizontal plane was reconstructed from the two vertical plane data in different directions. A detailed simulation code based on FEM was applied to the experimental analysis. The calculated velocity distributions were consistent with the experimental data.

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.

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