Drop impact into a deep pool: vortex shedding and jet formation

2015 ◽  
Vol 764 ◽  
Author(s):  
G. Agbaglah ◽  
M.-J. Thoraval ◽  
S. T. Thoroddsen ◽  
L. V. Zhang ◽  
K. Fezzaa ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Single Drop ◽  
Jet Formation ◽  
X Ray Imaging ◽  
Multiple Jets ◽  
Experimental Parameters ◽  
Single Jet ◽  
The Impact ◽  
Two Jets

AbstractOne of the simplest splashing scenarios results from the impact of a single drop on a deep pool. The traditional understanding of this process is that the impact generates an axisymmetric sheet-like jet that later breaks up into secondary droplets. Recently it was shown that even this simplest of scenarios is more complicated than expected because multiple jets can be generated from a single impact event and there are transitions in the multiplicity of jets as the experimental parameters are varied. Here, we use experiments and numerical simulations of a single drop impacting on a deep pool to examine the transition from impacts that produce a single jet to those that produce two jets. Using high-speed X-ray imaging methods we show that vortex separation within the drop leads to the formation of a second jet long after the formation of the ejecta sheet. Using numerical simulations we develop a phase diagram for this transition and show that the capillary number is the most appropriate order parameter for the transition.

Evolution of the ejecta sheet from the impact of a drop with a deep pool

2011 ◽  
Vol 690 ◽  
pp. 5-15 ◽  
Author(s):  
L. V. Zhang ◽  
J. Toole ◽  
K. Fezzaa ◽  
R. D. Deegan
Keyword(s):  
Reynolds Number ◽  
Deep Layer ◽  
Power Laws ◽  
Single Drop ◽  
X Ray ◽  
X Ray Imaging ◽  
Time Position ◽  
High Reynolds ◽  
The Impact ◽  
Two Jets

AbstractWe used optical and X-ray imaging to observe the formation of jets from the impact of a single drop with a deep layer of the same liquid. For high Reynolds number there are two distinct jets: the thin, fast and early-emerging ejecta; and the slow, thick and late-emerging lamella. For low Reynolds number the two jets merge into a single continuous jet, the structure of which is determined by the distinct contributions of the lamella and the ejecta. We measured the emergence time, position and speed of the ejecta sheet, and find that these scale as power laws with the impact speed and the viscosity. We identified the origin of secondary droplets with the breakup of the lamella and the ejecta jets, and show that the size of the droplets is not a good indicator of their origin.

Numerical simulation of humidification and heating during inspiration within an adult nose

2012 ◽  
Vol 50 (2) ◽  
pp. 157-164
Author(s):  
F. Sommer ◽  
R. Kroger ◽  
J. Lindemann
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Middle Turbinate ◽  
Multislice Ct ◽  
Respiratory Cycle ◽  
In Vivo Measurements ◽  
Airflow Distribution ◽  
The Impact ◽  
Human Nose

Background: The temperature of inhaled air is highly relevant for the humidification process. Narrow anatomical conditions limit possibilities for in vivo measurements. Numerical simulations offer a great potential to examine the function of the human nose. Objective: In the present study, the nasal humidification of inhaled air was simulated simultaneously with temperature distribution during a respiratory cycle. Methods: A realistic nose model based on a multislice CT scan was created. The simulation was performed by the Software Fluent(r). Boundary conditions were based on previous in vivo measurements. Inhaled air had a temperature of 20(deg)C and relative humidity of 30%. The wall temperature was assumed to be variable from 34(deg)C to 30(deg)C with constant humidity saturation of 100% during the respiratory cycle. Results: A substantial increase in temperature and humidity can be observed after passing the nasal valve area. Areas with high speed air flow, e.g. the space around the turbinates, show an intensive humidification and heating potential. Inspired air reaches 95% humidity and 28(deg)C within the nasopharynx. Conclusion: The human nose features an enormous humidification and heating capability. Warming and humidification are dependent on each other and show a similar spacial pattern. Concerning the climatisation function, the middle turbinate is of high importance. In contrast to in vivo measurements, numerical simulations can explore the impact of airflow distribution on nasal air conditioning. They are an effective method to investigate nasal pathologies and impacts of surgical procedures.

scholarly journals Growth and instability of the liquid rim in the crown splash regime

2014 ◽  
Vol 752 ◽  
pp. 485-496 ◽  
Author(s):  
G. Agbaglah ◽  
R. D. Deegan
Keyword(s):  
Thin Film ◽  
High Speed ◽  
Unstable Mode ◽  
Linear Stability Theory ◽  
Scaling Relations ◽  
X Ray ◽  
X Ray Imaging ◽  
Secondary Droplets ◽  
The Impact ◽  
Good Agreement

AbstractWe study the formation, growth and disintegration of jets following the impact of a drop on a thin film of the same liquid for $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{We}<1000$ and $\mathit{Re}<2000$ using a combination of numerical simulations and linear stability theory (Agbaglah, Josserand & Zaleski, Phys. Fluids, vol. 25, 2013, 022103). Our simulations faithfully capture this phenomena and are in good agreement with experimental profiles obtained from high-speed X-ray imaging. We obtain scaling relations from our simulations and use these as inputs to our stability analysis. The resulting predictions for the most unstable wavelength are in excellent agreement with experimental data. Our calculations show that the dominant destabilizing mechanism is a competition between capillarity and inertia but that deceleration of the rim provides an additional boost to growth. We also predict over the entire parameter range of our study the number and timescale for formation of secondary droplets formed during a splash, based on the assumption that the most unstable mode sets the droplet number.

scholarly journals On compression and damage evolution in two thermoplastics

2017 ◽  
Vol 473 (2197) ◽  
pp. 20160495 ◽  
Author(s):  
N. K. Bourne ◽  
S. C. Garcea ◽  
D. S. Eastwood ◽  
S. Parry ◽  
C. Rau ◽  
...  
Keyword(s):  
High Speed ◽  
Deformation Behaviour ◽  
Three Dimensional ◽  
Spatial And Temporal Variation ◽  
High Speed Photography ◽  
Radial Deformation ◽  
X Ray Imaging ◽  
Series Of Experiments ◽  
The Impact ◽  
Continuous Range

The well-known Taylor cylinder impact test, which follows the impact of a flat-ended cylindrical rod onto a rigid stationary anvil, is conducted over a range of impact speeds for two polymers, polytetrafluoroethylene (PTFE) and polyetheretherketone (PEEK). In previous work, experiments and a model were developed to capture the deformation behaviour of the cylinder after impact. These works showed a region in which spatial and temporal variation of both longitudinal and radial deformation provided evidence of changes in phase within the material. In this further series of experiments, this region is imaged in a range of impacted targets at the Diamond synchrotron. Further techniques were fielded to resolve compressed regions within the recovered polymer cylinders that showed a fracture zone in the impact region. The combination of macroscopic high-speed photography and three-dimensional X-ray imaging has identified the development of failure with these polymers and shown that there is no abrupt transition in behaviours but rather a continuous range of responses to competing operating mechanisms. The behaviours noted in PEEK in these polymers show critical gaps in understanding of polymer high strain-rate response.

scholarly journals Synchronized Multiple Drop Impacts into a Deep Pool

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 141 ◽  
Author(s):  
Manfredo Guilizzoni ◽  
Maurizio Santini ◽  
Stephanie Fest-Santini
Keyword(s):  
Fluid Dynamics ◽  
High Speed ◽  
Laboratory Experiments ◽  
Distilled Water ◽  
Single Drop ◽  
Two Phase ◽  
Wide Range ◽  
Computational Fluid Dynamics Cfd ◽  
Drop Impacts ◽  
The Impact

Drop impacts (onto dry or wet surfaces or into deep pools) are important in a wide range of applications, and, consequently, many studies, both experimental and numerical, are available in the literature. However, such works are focused either on statistical analyses of drop populations or on single drops. The literature is heavily lacking in information about the mutual interactions between a few drops during the impact. This work describes a computational fluid dynamics (CFD) study on the impact of two, three, and four synchronized drops into a deep pool. The two-phase finite-volume solver interFoam of the open source CFD package OpenFOAM® was used. After validation with respect to high speed videos, to confirm the performance of the solver in this field, impact conditions and aspects that would have been difficult to obtain and to study in experiments were investigated: namely, the energy conversion during the crater evolution, the effect of varying drop interspace and surface tension, and multiple drop impacts. The results show the very significant effect of these aspects. This implies that an extension of the results of single-drop, distilled-water laboratory experiments to real applications may not be reliable.

scholarly journals Generation and breakup of Worthington jets after cavity collapse. Part 1. Jet formation

2010 ◽  
Vol 663 ◽  
pp. 293-330 ◽  
Author(s):  
STEPHAN GEKLE ◽  
J. M. GORDILLO
Keyword(s):  
Flow Structure ◽  
High Speed ◽  
Liquid Surface ◽  
Circular Disk ◽  
Boundary Integral ◽  
Analytical Modelling ◽  
Acceleration Region ◽  
Jet Formation ◽  
Cavity Collapse ◽  
The Impact

At the beginning of the last century Worthington and Cole discovered that the high-speed jets ejected after the impact of an axisymmetric solid on a liquid surface are intimately related to the formation and collapse of an air cavity created in the wake of the impactor. In this paper, we combine detailed boundary-integral simulations with analytical modelling to describe the formation of such Worthington jets after the impact of a circular disk on water. We extend our earlier model in Gekle et al. (Phys. Rev. Lett., vol. 102, 2009a, 034502), valid for describing only the jet base dynamics, to describe the whole jet. We find that the flow structure inside the jet may be divided into three different regions: the axial acceleration region, where the radial momentum of the incoming liquid is converted to axial momentum; the ballistic region, where fluid particles experience no further acceleration and move constantly with the velocity obtained at the end of the acceleration region; and the jet tip region, where the jet eventually breaks into droplets. From our modelling of the ballistic region we conclude that, contrary to the case of other physical situations where high-speed jets are also ejected, the types of Worthington jets studied here cannot be described using the theory of hyperbolic jets of Longuet-Higgins (J. Fluid Mech., vol. 127, 1983, p. 103). Most importantly, we find that the velocity and the shape of the ejected jets can be well predicted at any instant in time with the only knowledge of quantities obtained before pinch-off occurs. This fact allows us to provide closed expressions for the jet velocity and the sizes of the ejected droplets as a function of the velocity and the size of the impactor. We show that our results are also applicable to Worthington jets emerging after the collapse of a bubble growing from an underwater nozzle, although this system creates thicker jets than the disk impact.

scholarly journals Investigation of Shock Initiation in Covered Charges under Shock Wave and Fragment Impacts

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xingwang Chen ◽  
Jinxiang Wang ◽  
Kui Tang ◽  
Hongfei Wang ◽  
Yuanbo Li
Keyword(s):  
Shock Wave ◽  
Theoretical Model ◽  
Numerical Simulations ◽  
High Speed ◽  
Least Squares Method ◽  
Strong Shock ◽  
Protective Function ◽  
Shock Initiation ◽  
Metal Plates ◽  
The Impact

In the current work, a series of step-by-step research methods have been applied to address the damaging effects of near-field strong shock waves and high-speed fragments on covered charge. In the first step, the defects of covered plates due to high-speed fragments were simplified to penetrated notches, and then, these notches were used to evaluate the impact of shock wave loads on charges covered with metal plates. In the next step, we developed a theoretical model to take into account the shock initiation of charges covered with defected metal plates. Explosive initiation standards coupled with shock wave evolution characteristics were applied to specify the crucial conditions of explosive detonation. Finite element program, for instance, was applied for the simulation of shock initiation processes in pressed charges (when TNT was covered with a steel plate containing a penetrated notch), and then, numerical simulations were validated by experimental findings. Finally, the results obtained from the numerical simulations and theoretical model were applied to evaluate the impacts of shock wave intensity, the thickness of covered metal plate, and the geometrical features of penetrated notch on pressed charge shock initiation. The least squares method was applied to determine critical initiation criteria (n and K). Theoretical calculation results were found to be highly consistent with those obtained from numerical simulations, indicating that covered metal plates significantly contributed to charge protection. The results also revealed that notches could undermine the protective function of covered plates and the size and shape of notch significantly affected charge critical detonation distance. Critical detonation distances of noncontact explosions were found to be 25 and 81 mm for a 3 mm thick pressed TNT in the presence and absence of 45# steel-covered plate, respectively. According to the results, increase in the diameter of covered plates containing a cylindrical notch increased pressed TNT critical detonation distance. When dealing with a covered plate containing a normally reflected frustum notch, however, we figured out that any increase in normal reflection slope could decrease pressed TNT critical detonation distance.

scholarly journals Early-time jet formation in liquid–liquid impact problems: theory and simulations

2018 ◽  
Vol 856 ◽  
pp. 764-796 ◽  
Author(s):  
R. Cimpeanu ◽  
M. R. Moore
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Early Stage ◽  
Early Time ◽  
Leading Order ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Jet Velocity ◽  
The Impact ◽  
Wagner Theory

We perform a thorough qualitative and quantitative comparison of theoretical predictions and direct numerical simulations for the two-dimensional, vertical impact of two droplets of the same fluid. In particular, we show that the theoretical predictions for the location and velocity of the jet root are excellent in the early stages of the impact, while the predicted jet velocity and thickness profiles are also in good agreement with the computations before the jet begins to bend. By neglecting the role of the surrounding gas both before and after impact, we are able to use Wagner theory to describe the early-time structure of the impact. We derive the model for general droplet velocities and radii, which encompasses a wide range of impact scenarios from the symmetric impact of identical drops to liquid drops impacting a deep pool. The leading-order solution is sufficient to predict the curve along which the root of the high-speed jet travels. After moving into a frame fixed in this curve, we are able to derive the zero-gravity shallow-water equations governing the leading-order thickness and velocity of the jet. Our numerical simulations are performed in the open-source software Gerris, which allows for the level of local grid refinement necessary for a problem with such a wide variety of length scales. The numerical simulations incorporate more of the physics of the problem, in particular the surrounding gas, the fluid viscosities, gravity and surface tension. We compare the computed and predicted solutions for a range of droplet radii and velocities, finding excellent agreement in the early stage. In light of these successful comparisons, we discuss the tangible benefits of using Wagner theory to confidently track properties such as the jet-root location, jet thickness and jet velocity in future studies of splash jet/ejecta evolution.

Effects of Different Liquid Properties on the Characteristics of Impact-Generated High-Speed Liquid Jets

2011 ◽  
Vol 110-116 ◽  
pp. 370-376 ◽  
Author(s):  
Anirut Matthujak ◽  
Chaidet Kasamnimitporn ◽  
Wuttichai Sittiwong ◽  
Kulachate Pianthong
Keyword(s):  
High Speed ◽  
Physical Property ◽  
Ambient Air ◽  
Video Camera ◽  
Orifice Diameter ◽  
Liquid Jets ◽  
Jet Formation ◽  
Digital Video Camera ◽  
Maximum Penetration ◽  
The Impact

This paper describes the study of high-speed liquid jets injected in air from an orifice. The main focus is to study the effect of different liquid properties on the characteristics of the high-speed liquid jets injected in ambient air. The high-speed liquid jets are generated by the impact of a projectile, which known as impact acceleration method, launched in a horizontal single-stage power gun (HSSPG). The conical nozzle of 30° angle with the orifice diameter of 0.7 mm was used to generate the jets. The characteristics of high-speed jets were visualized by the high-speed digital video camera with shadowgraph optical arrangement. From the shadowgraph images, the jet formation, atomization, vaporization and shock waves were obviously observed. The maximum averaged velocity of water, alcohol, n-hexane, chloroform and glycerin jets is estimated to be 1,669.03 m/s, 1,548.59 m/s, 1,420.44 m/s, 1,204.46 m/s and 1,496.97 m/s, respectively. That effect on the maximum penetration distance of the water jet is longer than that of all jets. Surface tension and latent heat are the significant physical property for jet formation, while density, kinematics viscosity and heat capacity are not.

Erosion and accretion by cratering impacts on rocky and icy bodies: Formulation of scaling relations for high-speed ejecta

2021 ◽  
Author(s):  
Hidenori Genda ◽  
Ryuki Hyodo
Keyword(s):  
Point Source ◽  
Numerical Simulations ◽  
High Speed ◽  
Scaling Law ◽  
Large Body ◽  
Target Material ◽  
Target Surface ◽  
Impact Angle ◽  
Material Strength ◽  
The Impact

&lt;p&gt;Numerous small bodies inevitably lead to cratering impacts on large planetary bodies during planet formation and evolution. As a consequence of these small impacts, a fraction of the target material escapes from the gravity of the large body, and a fraction of the impactor material accretes onto the target surface, depending on the impact velocities and angles. Here, we study the mass of the high-speed ejecta that escapes from the target gravity by cratering impacts when material strength is neglected. We perform a large number of cratering impact simulations onto a planar rocky and icy targets using the smoothed particle hydrodynamics method. We show that the escape mass of the target material obtained from our numerical simulations agrees with the prediction of a scaling law under a point-source assumption when &lt;em&gt;v&lt;/em&gt;&lt;sub&gt;imp&lt;/sub&gt; &gt; ~ 10 &lt;em&gt;v&lt;/em&gt;&lt;sub&gt;esc&lt;/sub&gt;, where &lt;em&gt;v&lt;/em&gt;&lt;sub&gt;imp&lt;/sub&gt; is the impact velocity and &lt;em&gt;v&lt;/em&gt;&lt;sub&gt;esc&lt;/sub&gt; is the escape velocity of the target. However, we find that the point-source scaling law overestimates the escape mass up to a factor of ~ 70, depending on the impact angle, when &lt;em&gt;v&lt;/em&gt;&lt;sub&gt;imp&lt;/sub&gt; &lt; ~ 10 &lt;em&gt;v&lt;/em&gt;&lt;sub&gt;esc&lt;/sub&gt; (Figure 1). Using data obtained from numerical simulations, we derive a new scaling law for the escape mass of the target material

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