The Dynamics of Drop Impact

2002 ◽  
Author(s):  
Christophe Josserand
Keyword(s):  
Liquid Layer ◽  
Weber Number ◽  
Stokes Equations ◽  
Early Time ◽  
Mass Conservation ◽  
Viscous Effects ◽  
Time Dynamics ◽  
Similar Solutions ◽  
The Impact

Inkjet printing, rainfall, droplet collision in combustion chambers are different forms of drop impacts. The whole dynamics of these impacts is complex and remains far to be fully understood. In particular the role of the viscosity of the drop liquid is still hard to exhibit. In one hand, the early time of the impact should be considered inviscid, and viscous free calculation give a fair approximation of the short time dynamics. On the other hand, experimental evidences show that the transition between splashing dynamics and deposition is controlled by a so-called splashing parameter K = We · sqrt(Re), where the viscosity enter through the Reynolds number Re (We being the Weber number). Therefore the role of the viscosity for the early time of the impact needs to be elucidated. We will present numerical simulations of the impact of a drop on a liquid layer thanks to a volume of fluid technique (VOF), where the Navier-Stokes equations are solved for both liquid and gas phases. For a given Weber number, we will vary only the viscosity so that viscous effects can be emphasized. The calculation will also determine the relative spreading of the drop inside the liquid layer. For splashing behaviors, a jet is emitted soon after the initiation of the impact; contrarily, no jets are present when deposition happens. The pressure field and the velocity field are studied near the neck of the impact and show no specific dependance on the viscosity. However, viscous effects are observed through the diffusion of the vorticity from the interface into the liquid bulk. Therefore, the viscous length lv = sqrt(vt) controls the gradient fields at the impact and we observe that the width of the emitted jet is determined by this length. Therefore, applying mass conservation to a dynamical solution where a jet of width lv is created, we can estimate the balance between mass ejected by the falling drop with mass coming from a retracting jet. The growth of a jet is thus controlled by this mass balance and the splashing parameter law is retrieved. In particular, the viscous effects appear in the theory as a singular perturbation of the inviscid impact dynamics. Self-similar solutions of the impact are therefore considered in specific gometries. More information at http://www.lmm.jussieu.fr/MEMBRES/JOSSERAND/josserand.html.

Influence of Liquid Properties on Energy Conversion During Crown Evolution Following Drop Impact Upon Films

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Yujia Zhang ◽  
Peiqing Liu ◽  
Qiulin Qu ◽  
Fanglin Liu ◽  
Ramesh K. Agarwal
Keyword(s):  
Reynolds Number ◽  
Energy Conversion ◽  
Weber Number ◽  
Stokes Equations ◽  
Drop Impact ◽  
Navier Stokes ◽  
Impact Process ◽  
Vof Model ◽  
The Moment ◽  
The Impact

Abstract The energy conversion is proposed to analyze the effects of liquid properties on the formation of an ejecta sheet, prompt splashing, and crown evolution. The incompressible laminar Navier–Stokes equations coupled with the volume-of-fluid (VOF) model are solved numerically in an axisymmetric frame to simulate the impact process. Based on the energy conversion curves and liquid–gas interface shapes, the Weber number is shown to be the main dimensionless quantity controlling the impact process, especially with regard to crown evolution. However, the Reynolds number does have some influence on the drop impact process, especially during the stage of ejecta sheet formation and prompt splashing. By studying energy conversion during the impact process, the crown evolution is shown to be accelerated significantly with decreasing Weber number, but is hardly affected by the Reynolds number. A linear relation is found between the time to the moment of crown stabilization (when the crown height reaches its maximum value) and the square root of the Weber number. The relationship between the Weber number and the energy distribution at the moment of crown stabilization is also studied.

High Speed Liquid Impact Onto Wetted Solid Surfaces

1994 ◽  
Vol 116 (2) ◽  
pp. 345-348 ◽  
Author(s):  
H. H. Shi ◽  
J. E. Field ◽  
C. S. J. Pickles
Keyword(s):  
Shock Wave ◽  
Liquid Layer ◽  
Solid Surface ◽  
High Speed ◽  
Shear Failure ◽  
Soda Lime ◽  
Liquid Jet ◽  
Soda Lime Glass ◽  
The Impact

The mechanics of impact by a high-speed liquid jet onto a solid surface covered by a liquid layer is described. After the liquid jet contacts the liquid layer, a shock wave is generated, which moves toward the solid surface. The shock wave is followed by the liquid jet penetrating through the layer. The influence of the liquid layer on the side jetting and stress waves is studied. Damage sites on soda-lime glass, PMMA (polymethylmethacrylate) and aluminium show the role of shear failure and cracking and provide evidence for analyzing the impact pressure on the wetted solids and the spatial pressure distribution. The liquid layer reduces the high edge impact pressures, which occur on dry targets. On wetted targets, the pressure is distributed more uniformly. Despite the cushioning effect of liquid layers, in some cases, a liquid can enhance material damage during impact due to penetration and stressing of surface cracks.

Perturbation theory and numerical modelling of weakly and moderately nonlinear dynamics of the incompressible Richtmyer–Meshkov instability

2014 ◽  
Vol 751 ◽  
pp. 432-479 ◽  
Author(s):  
A. L. Velikovich ◽  
M. Herrmann ◽  
S. I. Abarzhi
Keyword(s):  
Perturbation Theory ◽  
Stokes Equations ◽  
Early Time ◽  
Inviscid Flow ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Comput Phys ◽  
Acceleration And Deceleration ◽  
Simulation Results ◽  
The Impact

AbstractA study of incompressible two-dimensional (2D) Richtmyer–Meshkov instability (RMI) by means of high-order perturbation theory and numerical simulations is reported. Nonlinear corrections to Richtmyer’s impulsive formula for the RMI bubble and spike growth rates have been calculated for arbitrary Atwood number and an explicit formula has been obtained for it in the Boussinesq limit. Conditions for early-time acceleration and deceleration of the bubble and the spike have been elucidated. Theoretical time histories of the interface curvature at the bubble and spike tip and the profiles of vertical and horizontal velocities have been calculated and favourably compared to simulation results. In our simulations we have solved 2D unsteady Navier–Stokes equations for immiscible incompressible fluids using the finite volume fractional step flow solver NGA developed by Desjardins et al. (J. Comput. Phys., vol. 227, 2008, pp. 7125–7159) coupled to the level set based interface solver LIT (Herrmann, J. Comput. Phys., vol. 227, 2008, pp. 2674–2706). We study the impact of small amounts of viscosity on the flow dynamics and compare simulation results to theory to discuss the influence of the theory’s ideal inviscid flow assumption.

scholarly journals Delayed Leidenfrost phenomenon during impact of elastic fluid droplets

2020 ◽  
Vol 476 (2243) ◽  
pp. 20200556
Author(s):  
Purbarun Dhar ◽  
Soumya Ranjan Mishra ◽  
Ajay Gairola ◽  
Devranjan Samanta
Keyword(s):  
Weber Number ◽  
Polymer Concentration ◽  
Time Period ◽  
Increasing Trend ◽  
Viscoelastic Effects ◽  
Critical Weber Number ◽  
Leidenfrost Temperature ◽  
Elastic Fluids ◽  
The Impact

This article highlights the role of non-Newtonian (elastic) effects on the droplet impact phenomenon at temperatures considerably higher than the boiling point, especially at or above the Leidenfrost regime. The Leidenfrost point (LFP) was found to decrease with an increase in the impact Weber number (based on the velocity just before the impact) for fixed polymer (polyacrylamide) concentrations. Water droplets fragmented at very low Weber numbers (approx. 22), whereas the polymer droplets resisted fragmentation at much higher Weber numbers (approx. 155). We also varied the polymer concentration and observed that, up to 1000 ppm, the LFP was higher than that for water. This signifies that the effect can be delayed by the use of elastic fluids. We have shown the possible role of elastic effects (manifested by the formation of long lasting filaments) during retraction in the increase of the LFP. However, for 1500 ppm, the LFP was lower than that for water, but had a similar residence time during the initial impact. In addition, we studied the role of the Weber number and viscoelastic effects on the rebound behaviour at 405°C. We observed that the critical Weber number up to the point at which the droplet resisted fragmentation at 405°C increased with the polymer concentration. In addition, for a fixed Weber number, the droplet rebound height and the hovering time period increased up to 500 ppm, and then decreased. Similarly, for fixed polymer concentrations like 1000 and 1500 ppm, the rebound height showed an increasing trend up to certain a certain Weber number and then decreased. This non-monotonic behaviour of rebound heights was attributed to the observed diversion of the rebound kinetic energy to rotational energy during the hovering phase. Finally, a relationship between the non-dimensional Leidenfrost temperature and the associated Weber and Weissenberg numbers is developed, and a scaling relation is proposed.

Impact and Dispersion of Liquid Filled Cylinders

2006 ◽  
Vol 128 (6) ◽  
pp. 1295-1307
Author(s):  
John Borg ◽  
Susan Bartyczak ◽  
Nancy Swanson ◽  
John R. Cogar
Keyword(s):  
Vacuum Chamber ◽  
Early Time ◽  
Impact Dynamics ◽  
Expansion Velocity ◽  
Late Time ◽  
Thin Wall ◽  
Computational Results ◽  
Time Dynamics ◽  
Cylindrical Target ◽  
The Impact

The computational and experimental results of impact loading a thin wall liquid filled cylindrical target within a vacuum chamber are presented. The impact velocity ranges from 2.2 to 4.2km∕s. Both experimental and computational results are presented. It will be shown that impact dynamics and the early time fluid expansion are well modeled and understood. This includes the mass distribution and resulting expansion velocity. However, the late time dynamics, which includes the liquid breakup and droplet formation process of impacted liquid filled cylinders, is not well understood.

Response of Beams Under the Impact of Freak Waves

2014 ◽  
Author(s):  
Zhe Hu ◽  
Wenyong Tang ◽  
Hongxiang Xue ◽  
Shaofei Ren
Keyword(s):  
Stokes Equations ◽  
Mass Conservation ◽  
Structural Safety ◽  
The Sea Of Japan ◽  
Numerical Wave Tank ◽  
Freak Waves ◽  
Wave Tank ◽  
Freak Wave ◽  
Numerical Wave ◽  
The Impact

Recently the research on freak waves has focused on the formation mechanism as well as the experimental and numerical simulation, however the study of freak waves’ action on marine structures which is often confined to numerical methods is still not much. As beams are often studied as the simplified model of plates for structural safety assessment, in this paper, the response of a beam which is hit by a 2-D freak wave is studied. The freak wave is generated in a numerical wave tank (NWT) which solves the 2-D incompressible Navier-Stokes equations. The freak wave is based on the data of real sea condition in the Sea of Japan. An efficient wave absorbing method which satisfies the mass conservation is applied in the numerical wave tank. The influence of the beam’s motion on the freak wave fluid field is also considered in this paper, as well as different boundary conditions of the beam. It is found that the natural frequency has a great impact on the response of the beam.

scholarly journals CD73 Promotes Age-Dependent Accretion of Atherosclerosis

2020 ◽  
Vol 40 (1) ◽  
pp. 61-71 ◽  
Author(s):  
Nadia R. Sutton ◽  
Diane Bouïs ◽  
Kris M. Mann ◽  
Imran M. Rashid ◽  
Alexandra L. McCubbrey ◽  
...  
Keyword(s):  
Plasma Lipid ◽  
Early Time ◽  
Adenosine Monophosphate ◽  
Lipid Levels ◽  
Surface Versus ◽  
Lipid Catabolism ◽  
Significant Reversal ◽  
Age Dependent ◽  
The Impact

Objective: CD73 is an ectonucleotidase which catalyzes the conversion of AMP (adenosine monophosphate) to adenosine. Adenosine has been shown to be anti-inflammatory and vasorelaxant. The impact of ectonucleotidases on age-dependent atherosclerosis remains unclear. Our aim was to investigate the role of CD73 in age-dependent accumulation of atherosclerosis. Approach and results: Mice doubly deficient in CD73 and ApoE (apolipoprotein E; ( cd73 − /− /apoE −/− ) were generated, and the extent of aortic atherosclerotic plaque was compared with apoE −/− controls at 12, 20, 32, and 52 weeks. By 12 weeks of age, cd73 −/− /apoE −/− mice exhibited a significant increase in plaque (1.4±0.5% of the total vessel surface versus 0.4±0.1% in apoE −/− controls, P <0.005). By 20 weeks of age, this difference disappeared (2.9±0.4% versus 3.3±0.7%). A significant reversal in phenotype emerged at 32 weeks (9.8±1.2% versus 18.3±1.4%; P <0.0001) and persisted at the 52 week timepoint (22.4±2.1% versus 37.0±2.1%; P <0.0001). The inflammatory response to aging was found to be comparable between cd73 −/− /apoE −/− mice and apoE −/− controls. A reduction in lipolysis in CD73 competent mice was observed, even with similar plasma lipid levels ( cd73 −/− /apoE −/− versus apoE −/− at 12 weeks [16.2±0.7 versus 9.5±1.4 nmol glycerol/well], 32 weeks [24.1±1.5 versus 7.4±0.4 nmol/well], and 52 weeks [13.8±0.62 versus 12.7±2.0 nmol/well], P <0.001). Conclusions: At early time points, CD73 exerts a subtle antiatherosclerotic influence, but with age, the pattern reverses, and the presence of CD73 promoted suppression of lipid catabolism.

Intergroup Threat and Outgroup Attitudes

2013 ◽  
Vol 44 (5) ◽  
pp. 311-319 ◽  
Author(s):  
Marco Brambilla ◽  
David A. Butz
Keyword(s):  
Gay Men ◽  
Social Group ◽  
Welfare Recipients ◽  
Intergroup Attitudes ◽  
Social Policies ◽  
Intergroup Threat ◽  
Economic Threat ◽  
The Impact ◽  
General Climate

Two studies examined the impact of macrolevel symbolic threat on intergroup attitudes. In Study 1 (N = 71), participants exposed to a macrosymbolic threat (vs. nonsymbolic threat and neutral topic) reported less support toward social policies concerning gay men, an outgroup whose stereotypes implies a threat to values, but not toward welfare recipients, a social group whose stereotypes do not imply a threat to values. Study 2 (N = 78) showed that, whereas macrolevel symbolic threat led to less favorable attitudes toward gay men, macroeconomic threat led to less favorable attitudes toward Asians, an outgroup whose stereotypes imply an economic threat. These findings are discussed in terms of their implications for understanding the role of a general climate of threat in shaping intergroup attitudes.

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