Studies of two-dimensional liquid-wedge impact and their relevance to liquid-drop impact problems

1985 ◽  
Vol 401 (1821) ◽  
pp. 225-249 ◽  
Keyword(s):  
High Speed ◽  
Liquid Drop ◽  
Time History ◽  
Drop Impact ◽  
High Speed Photography ◽  
Two Dimensional ◽  
Surface Geometry ◽  
Repeated Impact ◽  
Liquid Impact ◽  
The Impact

In the initial stage of liquid-drop impact, the contact region expands faster than the wave speed in the liquid. This causes compressible behaviour in the liquid, and high transient pressures. High-velocity jetting results when the wave motion in the liquid overtakes the expanding contact edge and moves up the free surface of the drop. The detailed pressure fields in this early time history of impact have been calculated by Lesser ( Proc . R . Soc . Lond . 377, 289 (1981)) for both two and three-dimensional liquid masses and for targets of finite admittance. An important result is that the edge pressures exceed the central ‘water-hammer’ pressure 3ρ 0 CU i and at the time of shock-detachment approach ca . 3ρ 0 CU i . At this stage the edge pressures, for both spherical drops and two-dimensional liquid wedges, depend only on the impact velocity and the instantaneous angle between the liquid and solid surfaces. This suggests that the essential features of the early stage of liquid impact can be usefully studied by producing impacts with two-dimensional liquid wedges, and predicted data for pressures, shock angles and velocities are presented. Experiments are described for producing impacts with preformed shapes by using water-gelatine mixtures and observing the impact events with high-speed photography. The results confirm the main features of the model and give information on edge pressures, jetting, cavitation in the liquid and the effect of the admittance of the solid. The relevance of the results to the damage and erosion of materials subjected to liquid impact is discussed. In particular, it is possible to explain the apparently low damage-threshold of some materials, the form of damage and its development with repeated impact. The study highlights the importance of the detailed surface geometry in the region of contact.

The brittle fracture of solids by liquid impact, by solid impact, and by shock

1964 ◽  
Vol 282 (1390) ◽  
pp. 331-352 ◽  
Keyword(s):  
Surface Wave ◽  
High Velocity ◽  
High Speed ◽  
Turbine Blades ◽  
Explosive Loading ◽  
Back Surface ◽  
High Speed Photography ◽  
Liquid Mass ◽  
Liquid Impact ◽  
The Impact

The type of stress pulse produced when a liquid mass strikes a solid at high velocity is first examined. Compressible behaviour, giving rise to a sharp peak of pressure, is found to occur in the initial stages of the impact. The duration of this peak depends on the dimensions and impact velocity of the liquid mass, and also on the compressible wave velocity for the liquid. A comparison is made with pulses produced by solid/solid impact and by the detonation of small quantities of explosive. Both the high-speed liquid impact and the explosive loading give intense pulses of duration only a few microseconds. A solid/solid impact has, by comparison, a much longer impact time of the order of hundreds of microseconds. The fracture of glasses and hard polymers using these three types of loading is described. The development of fracture is followed by high-speed photography. Differences in the modes of fracture are attributed to variations in the shape and duration of the applied stress pulses. Short circumferential fractures produced around the loaded area in liquid impact and explosive loading are shown to be initiated by the Rayleigh surface wave at points where flaws existed. More complex fracture patterns on the front surfaces of plates are due to the reinforcement of the surface wave with components of stress waves reflected from the back surface. A combination of impact loading and etching makes it possible to investigate the distribution and depths of flaws, their role in the fracture process, and the effect which etching has upon them. The observation on the deformation produced in solids by liquid impact has practical significance in the problem of supersonic aircraft flying through rain and in the erosion of turbine blades moving at high velocity through wet steam.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Stress waves, deformation and fracture caused by liquid impact

1966 ◽  
Vol 260 (1110) ◽  
pp. 86-93 ◽  
Keyword(s):  
Surface Wave ◽  
High Speed ◽  
Rear Surface ◽  
Front Surface ◽  
Back Surface ◽  
High Speed Photography ◽  
Ring Fracture ◽  
Liquid Mass ◽  
Liquid Impact ◽  
The Impact

When a liquid mass strikes a solid surface, compressible behaviour, giving rise to a sharp peak of pressure, may occur in the initial stages of the impact. The duration of the peak depends on the dimensions and impact velocity of the liquid mass, and also on the compressional wave velocity for the liquid. There are similarities between this type of loading and that produced by the detonation of small quantities of explosive, since both give intense pressure peaks of only a few microseconds’ duration. The fracture and deformation of glasses, hard polymers, single crystal and ceramic materials by liquid impact at velocities up to 1000 m/s is described and briefly compared with that produced by solid/solid impact and explosive loading. The detailed development of fracture has been followed by high speed photography. In brittle solids the main characteristics of damage on the front surface is a ring fracture surrounding a largely undamaged area. The ring fracture forms at the edge of the loaded area where high tensile forces develop during impact. Outside this main ring of fracture short circumferential cracks occur; these are shown to be initiated by the Rayleigh surface wave at points where flaws existed. More complex fracture patterns which appear on the front surface of plates are due to the reinforcement of the surface wave with components of stress reflected from the back surface. Thin plate specimens often exhibit ‘scabbing’ fracture at the rear surface; in brittle materials of low attenuation this form of damage can be of prime importance. Since the stress pulses producing fracture during liquid impact are short the fractures themselves remain short and discrete. By a combination of impact loading and etching it is possible to investigate the distribution and depth of flaws, their role in the fracture process, and the effect which etching has upon them.

Drop Impact Dynamics: Impact Force and Stress Distributions

2021 ◽  
Vol 54 (1) ◽  
Author(s):  
Xiang Cheng ◽  
Ting-Pi Sun ◽  
Leonardo Gordillo
Keyword(s):  
High Speed ◽  
Impact Force ◽  
Drop Impact ◽  
Impact Dynamics ◽  
Annual Review ◽  
Publication Date ◽  
High Speed Photography ◽  
Stress Distributions ◽  
Wide Range ◽  
The Impact

Dynamic variables of drop impact such as force, drag, pressure, and stress distributions are key to understanding a wide range of natural and industrial processes. While the study of drop impact kinematics has been in constant progress for decades thanks to high-speed photography and computational fluid dynamics, research on drop impact dynamics has only peaked in the last 10 years. Here, we review how recent coordinated efforts of experiments, simulations, and theories have led to new insights on drop impact dynamics. Particularly, we consider the temporal evolution of the impact force in the early- and late-impact regimes, as well as spatiotemporal features of the pressure and shear-stress distributions on solid surfaces. We also discuss other factors, including the presence of water layers, air cushioning, and nonspherical drop geometry, and briefly review granular impact cratering by liquid drops as an example demonstrating the distinct consequences of the stress distributions of drop impact. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Hydrodynamic Phenomena During High-Speed Collision Between Liquid Droplet and Rigid Plane

1973 ◽  
Vol 95 (2) ◽  
pp. 276-292 ◽  
Author(s):  
Yen C. Huang ◽  
F. G. Hammitt ◽  
W-J Yang
Keyword(s):  
High Speed ◽  
Liquid Droplet ◽  
Lateral Flow ◽  
Maximum Pressure ◽  
Two Dimensional ◽  
Droplet Shape ◽  
One Dimensional ◽  
Liquid Impact ◽  
The Impact ◽  
Impact Problem

The dynamics of high-speed impact between a compressible water droplet and a rigid solid surface is investigated analytically. The purpose of the study is to examine the mechanism leading to the erosion of a material due to liquid impingement. A Compressible-Cell-and-Marker (ComCAM) numerical method is developed to solve the differential equations governing the unsteady, two-dimensional liquid-solid impact phenomena. The method is designed to solve this unsteady portion up until the flow reasonably approaches the steady-state solution. The validity of the method is confirmed by comparing its numerical results with the idealized exact solution for the classical one-dimensional liquid impact problem. The accuracy of the numerical reresults is found to be very good in that only slight numerical oscillations occur. Viscosity and surface tension are neglected as seems resaonable with the relatively large drops and high velocities considered. Pressure and velocity distributions are solved as a function of time. The deformation of a drop is also recorded for three different shapes: cylindrical, spherical, and a combination of the two, which may more closely model the actual droplet shapes to be encountered in such impacts. Typical liquid impact Mach numbers of 0.2 and 0.5 (sonic velocity referred to water) were studied. Thus impact velocities of about 980 and 2450 fps are considered. Compression predominates during the early stages of the impact, while rarefaction governs later, during which time the radial lateral flow velocity exceeds the initial impact velocity. The reflection of compression waves and the lateral flow leads to the possibility of cavitation within the drop, due to the consequent generation of negative pressures, exists. The maximum pressure calculated in this two-dimensional liquid impact problem is found to be less than the one-dimensional maximum pressure for all three different droplets in various degrees. It is found that droplet shape impact angle and liquid impact Mach number are the only important parameters of the problem for a flat fully-rigid target surface. As more time elapses, i.e., up to 2–3 μsec for a 2.0 mm-dia drop, the maximum pressure shifts from the center of the contact area radially outward, while the pressure at the center attenuates rapidly toward conventional stagnation pressure.

scholarly journals Detonation effects of shallow buried explosive in sandy soil on target plate acceleration in a small-scale blast test

2018 ◽  
Vol 192 ◽  
pp. 02028
Author(s):  
Hassan Zulkifli Abu ◽  
Ibrahim Aniza ◽  
Mohamad Nor Norazman
Keyword(s):  
Sandy Soil ◽  
High Speed ◽  
Early Stage ◽  
Time History ◽  
Video Camera ◽  
Small Scale ◽  
Target Plate ◽  
Air Blast ◽  
High Speed Video Camera ◽  
The Impact

Small-scale blast tests were carried out to observe and measure the influence of sandy soil towards explosive blast intensity. The tests were to simulate blast impact imparted by anti-vehicular landmine to a lightweight armoured vehicle (LAV). Time of occurrence of the three phases of detonation phase in soil with respect to upward translation time of the test apparatus were recorded using high-speed video camera. At the same time the target plate acceleration was measured using shock accelerometer. It was observed that target plate deformation took place at early stage of the detonation phase before the apparatus moved vertically upwards. Previous data of acceleration-time history and velocity-time history from air blast detonation were compared. It was observed that effects of soil funnelling on blast wave together with the impact from soil ejecta may have contributed to higher blast intensity that characterized detonation in soil, where detonation in soil demonstrated higher plate velocity compared to what occurred in air blast detonation.

scholarly journals Granular impact cratering by liquid drops: Understanding raindrop imprints through an analogy to asteroid strikes

2014 ◽  
Vol 112 (2) ◽  
pp. 342-347 ◽  
Author(s):  
Runchen Zhao ◽  
Qianyun Zhang ◽  
Hendro Tjugito ◽  
Xiang Cheng
Keyword(s):  
High Speed ◽  
Granular Media ◽  
Liquid Drop ◽  
Impact Craters ◽  
High Speed Photography ◽  
Impact Cratering ◽  
Liquid Drops ◽  
Asteroid Impact ◽  
Liquid Marble ◽  
Crater Morphology

When a granular material is impacted by a sphere, its surface deforms like a liquid yet it preserves a circular crater like a solid. Although the mechanism of granular impact cratering by solid spheres is well explored, our knowledge on granular impact cratering by liquid drops is still very limited. Here, by combining high-speed photography with high-precision laser profilometry, we investigate liquid-drop impact dynamics on granular surface and monitor the morphology of resulting impact craters. Surprisingly, we find that despite the enormous energy and length difference, granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters. Inspired by this similarity, we integrate the physical insight from planetary sciences, the liquid marble model from fluid mechanics, and the concept of jamming transition from granular physics into a simple theoretical framework that quantitatively describes all of the main features of liquid-drop imprints in granular media. Our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes.

Hydraulic Performance and Jet Breakup Characteristics of the Impact Sprinkler with Circular and Non-circular Nozzles

2019 ◽  
Vol 35 (6) ◽  
pp. 911-924 ◽  
Author(s):  
Yue Jiang ◽  
Hong Li ◽  
Chao Chen ◽  
Lin Hua ◽  
Daming Zhang
Keyword(s):  
High Speed ◽  
Cone Angle ◽  
Hydraulic Performance ◽  
High Speed Photography ◽  
Breakup Process ◽  
Breakup Length ◽  
Jet Breakup ◽  
Circular Jets ◽  
Square Jets ◽  
The Impact

HighlightsThe hydraulic performance of the impact sprinkler with circular and non-circular nozzles were measured.A High-Speed Photography (HSP) technique was employed to extract the jet breakup process of the impact sprinkler.Two index equations of jet characteristic lengths and equivalent diameters of non-circular nozzles were fitted. Abstract. An experiment was carried out to investigate the hydraulic performance of an impact sprinkler by using circular and non-circular nozzles. A High-Speed Photography (HSP) technique was employed to extract the breakup process and flow behavior of low-intermediate pressure water jets issued from the different types of orifices. These orifices were selected by the principle of equal flowrate with the same pressure. Moreover, two characteristic lengths: the jet breakup length and the initial amplitude of surface wave were measured. It was found that the sprinkler with circular nozzles produced the largest radius of throw followed by square nozzles and regular triangular nozzles when the cone angle of nozzle and pressure were unchanged, while the sprinkler with regular triangular nozzle had the best variation trend of water distribution and combination uniformity coefficient. Regular triangular jets exhibited a higher degree in breakup and the shortest breakup length compared with the square jets and the circular jets. The initial amplitudes of surface waves of regular triangular jets were larger than the square jets and the circular jets with the same cone angle. Two index equations of jet characteristic lengths and equivalent diameters of both circular and non-circular orifices were fitted with a relative error of less than 10%, which means the fitting formulas were accurate. Keywords: Breakup length, Fitting formula, Hydraulic performance, Initial amplitude, Non-circular jets.

Improved Two-Dimensional Dynamic Stall Prediction with Structured and Hybrid Numerical Methods

2011 ◽  
Vol 56 (4) ◽  
pp. 1-12 ◽  
Author(s):  
K. Richter ◽  
A. Le Pape ◽  
T. Knopp ◽  
M. Costes ◽  
V. Gleize ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Numerical Method ◽  
High Speed ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
Dynamic Stall ◽  
Two Dimensional ◽  
Layer Transition ◽  
The Impact

A joint comprehensive validation activity on the structured numerical method elsA and the hybrid numerical method TAU was conducted with respect to dynamic stall applications. To improve two-dimensional prediction, the influence of several factors on the dynamic stall prediction was investigated. The validation was performed for three deep dynamic stall test cases of the rotor blade airfoil OA209 against experimental data from two-dimensional pitching airfoil experiments, covering low-speed and high-speed conditions. The requirements for spatial discretization and for temporal resolution in elsA and TAU are shown. The impact of turbulence modeling is discussed for a variety of turbulence models ranging from one-equation Spalart–Allmaras-type models to state-of-the-art, seven-equation Reynolds stress models. The influence of the prediction of laminar/turbulent boundary layer transition on the numerical dynamic stall simulation is described. Results of both numerical methods are compared to allow conclusions to be drawn with respect to an improved prediction of dynamic stall.

scholarly journals Dynamic damage in carbon-fibre composites

2016 ◽  
Vol 374 (2071) ◽  
pp. 20160018 ◽  
Author(s):  
N. K. Bourne ◽  
S. Parry ◽  
D. Townsend ◽  
P. J. Withers ◽  
C. Soutis ◽  
...  
Keyword(s):  
Carbon Fibre ◽  
High Speed ◽  
Failure Modes ◽  
Structural Integrity ◽  
High Speed Photography ◽  
Compression Phase ◽  
Impact Surface ◽  
Fibre Composites ◽  
The Impact ◽  
Carbon Fibre Composites

The Taylor test is used to determine damage evolution in carbon-fibre composites across a range of strain rates. The hierarchy of damage across the scales is key in determining the suite of operating mechanisms and high-speed diagnostics are used to determine states during dynamic loading. Experiments record the test response as a function of the orientation of the cylinder cut from the engineered multi-ply composite with high-speed photography and post-mortem target examination. The ensuing damage occurs during the shock compression phase but three other tensile loading modes operate during the test and these are explored. Experiment has shown that ply orientations respond to two components of release; longitudinal and radial as well as the hoop stresses generated in inelastic flow at the impact surface. The test is a discriminant not only of damage thresholds but of local failure modes and their kinetics. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

A New Concept of Needle-Free Jet Injector by the Impact Driven Method

2017 ◽  
Vol 11 (1) ◽  
Author(s):  
Prachya Mukda ◽  
Kulachate Pianthong ◽  
Wirapan Seehanam
Keyword(s):  
High Speed ◽  
Liquid Jet ◽  
High Speed Photography ◽  
Free Jet ◽  
Impact Peak ◽  
Lower Pain ◽  
Jet Velocity ◽  
Commercial Device ◽  
Jet Injectors ◽  
The Impact

Currently, most of commercial needle-free jet injectors generate the liquid jet by a method called “driving object method” (DOM); however, the reliability and efficiency are still questioned. This paper proposes a new concept of jet generation method, known as “impact driven method” (IDM). A prototype of an IDM jet injector is designed, built, tested, and compared to a commercial device (Cool.click, Tigard, OR). Fundamental characteristics, i.e., the exit jet velocity and impact pressure, are measured. Jet injection processes are visualized both in air and in 20% polyacrylamide by high speed photography. In this study, from the prototype of the IDM jet injector, a maximum jet velocity of 400 m/s and impact peak pressure of 68 MPa can be obtained. It is clear that the IDM jet injector provides a double pulsed liquid jet, which is a major advantage over the commercial jet injector. Because, the first pulse gives a shorter erosion stage, and then, immediately the second pulse follows and provides a better penetration, wider lateral dispersion, and considerably less back splash. Hence, lower pain level and higher delivery efficiency should be achieved. It can be concluded that the IDM concept is highly feasible for implementation in real applications, either for human or animal injection. However, the control and accuracy of IDM still needs to be carefully investigated.

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