A photographic study of the impact between water drops and a surface moving at high speed

Wear ◽  
1960 ◽  
Vol 3 (6) ◽  
pp. 485
Keyword(s):  
High Speed ◽  
Water Drops ◽  
The Impact

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 - Observation of events leading to the formation of water drops which cause turbine blade erosion

1966 ◽  
Vol 260 (1110) ◽  
pp. 183-192 ◽  
Keyword(s):  
Turbine Blade ◽  
High Speed ◽  
Maximum Velocity ◽  
Low Pressure ◽  
Background Information ◽  
Maximum Diameter ◽  
Steam Turbines ◽  
Subsequent Formation ◽  
Water Drops ◽  
The Impact

The large blades required in the last low pressure stages of modern turbines of 350 MW and above makes them more susceptible to erosion by wet steam owing to the increase in blade tip velocity. A specially developed periscope combined with a cine camera has been used for viewing inside an operating turbine to record the flow of water over the fixed blades and the subsequent formation and stripping of the water drops which then impact on the moving blades causing erosion. The drops had a maximum diameter of 450 /mi and the estimated total mass of the drops impacting on the blades was only a few per cent of the mass flow of water condensed from the steam. This confirms that the condensed steam forms a fog of droplets which are so small that only a very small proportion of them is captured by the turbine surfaces to produce large drops capable of causing erosion. In addition to the direct practical value of these observations, the data provide background information in support of the high speed photographic studies of the drop-forming processes on a blade cascade in the laboratory. Experiments in a steam tunnel in which the turbine low pressure steam conditions can be simulated, indicate that drops of 350 to 1600 /xm leave the trailing edge of a blade and accelerate to a maximum velocity of 70 ft./s over a distance of about 1 in. in the blade wake. They are then caught in the main steam flow, which has a velocity of up to 1200 ft./s, where they are broken up and rapidly accelerated. Analysis of the cine films of observations in a turbine and in the steam tunnel gives the velocities and sizes of the drops causing turbine blade erosion.

Explosion of Drops Impacting Non-Wetting Rigid Surfaces

1992 ◽  
Vol 296 ◽  
Author(s):  
Clarence Zener ◽  
Dennis Prieve
Keyword(s):  
Impact Velocity ◽  
High Speed ◽  
High Speed Photography ◽  
Water Drops ◽  
Rigid Surfaces ◽  
The Impact

More than 100 years ago Worthington [1,2] reported his observations on drops exploding on impacting rigid surfaces they did not wet. Mercury was his favorite fluid, since mercury does not wet most solids. For water drops he had to especially “smoke” his surfaces to make them non-wetting. In his day high speed photography had not been developed, but he had learned to “stop” his falling drops by spark illumination. His drops had radii of typically 1 mm, fell from a height of ∼10 cm and ejected always an even number of spikes, typically ∼24. These spikes would shoot out from the impacted area at velocities several times higher than the impact velocity.

scholarly journals Collision of water drops with a thin cylinder

2021 ◽  
Vol 2057 (1) ◽  
pp. 012034
Author(s):  
A I Fedyushkin ◽  
A N Rozhkov ◽  
A O Rudenko
Keyword(s):  
Stainless Steel ◽  
High Speed ◽  
Video Recording ◽  
Frame Rate ◽  
Drop Diameter ◽  
Outer Diameter ◽  
Stainless Steel Capillary ◽  
Thin Cylinder ◽  
Water Drops ◽  
The Impact

Abstract The collision of water drops with a thin cylinder is studied. The droplet flight trajectory and the cylinder axis are mutually perpendicular. In the experiments, the drop diameter is 3 mm, and the diameter of horizontal stainless-steel cylinders is 0.4 and 0.8 mm. The drops are formed by a liquid slowly pumped through a vertical stainless-steel capillary with an outer diameter of 0.8 mm, from which droplets are periodically separated under the action of gravity. The droplet velocity before collision is defined by the distance between the capillary cut and the target (cylinder); in experiments, this distance is approximately 5, 10, and 20 mm. The drop velocities before the impact are estimated in the range of 0.2–0.5 m/s. The collision process is monitored by high-speed video recording methods with a frame rate of 240 and 960 Hz. The test liquids are water. Experiments and numerical simulation show that, depending on the drop impact height (droplets velocity) different scenarios of a drop collision with a thin cylinder are possible: a short-term recoil of a drop from an obstacle, a drop flowing around a cylindrical obstacle while maintaining the continuity of the drop, the breakup of a drop into two secondary drops, one of which can continue flight and the other one is captured by the cylinder, or both secondary droplets continue to fly, and the drop can be also captured by the cylinder, until the impact of the next drop(s) forces the accumulated drop to detach from the cylinder. Numerical modeling satisfactorily reproduces the phenomena observed in the experiment.

Experimental and Numerical Characterization of Drop Impact on a Hydrophobic Cylinder

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Javid Zohrabi Chakaneh ◽  
Seyed Javad Pishbin ◽  
Alireza Sheikhi Lotfabadi ◽  
Mohammad Passandideh-Fard
Keyword(s):  
High Speed ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Time Step ◽  
Cylinder Diameter ◽  
Numerical Characterization ◽  
Drop Generator ◽  
Water Drops ◽  
The Impact

In this paper, the impact of distilled water drops on hydrophobic cylinders is characterized using both experiments and numerical simulations. Water drops of 2.54 mm in diameter impact with a velocity of 1 m/s on hydrophobic cylinders. The corresponding Reynolds and Weber numbers are 2800 and 34, respectively. Three different stainless steel cylinders with diameters of 0.48 mm, 0.88 mm, and 1.62 mm were used. The surfaces of the cylinders were made hydrophobic using a special coating spray. An experimental setup consisting of a drop generator, a high-speed camera, a lighting system, and a photoelectric sensor was used to capture images of the impact with a time-step of 1 ms. The images were then analyzed using an image processing technique implemented in the matlab software. Both the centric and off-centric impacts were studied for each cylinder diameter. A numerical simulation of the impact was also obtained using an open-source code called OpenFOAM by employing its InterFoam solver. The numerical scheme used by the solver is the volume-of-fluid (VOF) method. The predicted images of the simulations were compared well with those of the captured photographs both qualitatively and quantitatively for the entire experiments. The behavior of the drop after the impact and the subsequent deformation on hydrophobic cylinders including flow instabilities, liquid breakup, and secondary drops formation were observed from both simulations and experiments. By decreasing the cylinder diameter, the breakup occurs sooner, and a smaller number of secondary drops are formed.

Time Evolutions of Water Drops Impacting on a Rotating Disk

2011 ◽  
Vol 354-355 ◽  
pp. 609-614
Author(s):  
Jing Yin Li ◽  
Xiao Fang Yuan ◽  
Qiang Han
Keyword(s):  
High Speed ◽  
Water Drop ◽  
Experimental Studies ◽  
Rotating Disk ◽  
Deposition Process ◽  
Video Camera ◽  
Rossby Number ◽  
High Speed Video Camera ◽  
Water Drops ◽  
The Impact

Experimental studies of a water drop impinging on a rotating disk using a high-speed video camera have been performed. The photos of the impact were analyzed in detail. Three kinds of the deposition patterns were observed with the variation in Rossby number. It is found that Rossby number plays an important role in the deposition process of the drop impacting on the rotating disk, leading to some new stages not observed for drop impact on a stationary plate.

The transitional regime between coalescing and splashing drops

1996 ◽  
Vol 306 ◽  
pp. 145-165 ◽  
Author(s):  
Martin Rein
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Impact Crater ◽  
High Speed Photography ◽  
Normal Impact ◽  
Transitional Regime ◽  
Water Drops ◽  
Crown Formation ◽  
The Impact

A drop that falls into a deep liquid can either coalesce with the receiving liquid and form a vortex ring or splash. Which phenomenon actually occurs depends on the impact conditions. When the impact conditions are gradually changed the transition between coalescence and splashing proceeds via a number of intermediate steps. These are studied by means of high-speed photography of the normal impact of water drops on a plane water surface. The characteristics of different flows that appear in the transitional regime and possible mechanisms causing these flows are discussed in detail. The phenomena considered include the rise of thick jets and the ejection of high-rising thin jets out of the impact crater, the entrainment of gas bubbles, crater dynamics, crown formation and the generation of splash droplets. Finally, a classification of the phenomena characteristic of the transitional regime is given.

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 - Disintegration of raindrops by shockwaves ahead of conical bodies

1966 ◽  
Vol 260 (1110) ◽  
pp. 153-160 ◽  
Keyword(s):  
High Speed ◽  
Empirical Relation ◽  
Aircraft Design ◽  
The Body ◽  
Drop Diameter ◽  
Steam Turbines ◽  
Supersonic Flight ◽  
Water Drops ◽  
Time Required ◽  
The Impact

When an aircraft flies at high speed through rain the impact of raindrops on the forward facing surfaces of the aircraft may cause severe erosion damage depending on the size and number of the drops, the speed of the aircraft and the time of flight in the rain. However, before the raindrops reach the aircraft surface they have to pass through a region where they are subjected to relative air velocities caused by the airflow round the aircraft surface. This is particularly applicable to supersonic flight when, in the region between the shockwaves and the aircraft surface, the raindrops may be exposed to air velocities large enough to disintegrate them. The raindrop disintegration is not an instantaneous event; it takes short but finite time and appears to be an erosion process whereby droplets are torn off the surface of the main drop until it is completely reduced to a fine mist. The degree of disintegration of a drop by the time it reaches the aircraft surface will depend on the magnitude of, and the exposure time to, the air velocity. For supersonic flight this time depends on the distance travelled by the drop between the shockwave and the aircraft surface. The experiments described had the object of determining the time required for high speed airstreams completely to disintegrate water drops. An empirical relation is postulated between D , the drop diameter, V , the airstream velocity and t , the time for complete disintegration. The paper considers a conical body at supersonic velocity in a raindrop environment, the body being of a shape typical of that envisaged for supersonic aircraft design. From the derived empirical relation for the time of disintegration of water drops the size of drops to be completely disintegrated when approaching the surface of cones of different vertex angles has been calculated for a range of flight Mach numbers. An experiment giving partial justification for computed results is described.

Normal impact of supercooled water drops onto a smooth ice surface: experiments and modelling

2017 ◽  
Vol 835 ◽  
pp. 1087-1107 ◽  
Author(s):  
Markus Schremb ◽  
Ilia V. Roisman ◽  
Cameron Tropea
Keyword(s):  
Layer Thickness ◽  
High Speed ◽  
A Priori ◽  
Supercooled Water ◽  
Layer Growth ◽  
Theoretical Modelling ◽  
Viscous Boundary Layer ◽  
Ice Surface ◽  
Water Drops ◽  
The Impact

The present study is devoted to the experimental investigation and theoretical modelling of the interaction between fluid flow and solidification during the impact of supercooled water drops onto an ice surface. Using a high-speed video system, the impact process is captured with a high spatial and temporal resolution in a side view. The lamella thinning and the residual ice layer thickness in the centre of impact are determined from the high-speed videos for varying drop and surface temperatures, and impact velocities. It is shown that the temperature of the impact surface has a negligible influence and the drop temperature has a dominating influence on the lamella thinning and the final ice layer thickness. For decreasing drop temperatures, higher freezing rates cause a decreased rate of lamella thinning and a larger thickness of the resulting ice layer. On the other hand, a higher impact velocity causes an increasing speed of lamella thinning and a smaller thickness of the resulting ice layer. Based on a postulated flow in the spreading lamella and considering the ice layer growth and the developing viscous boundary layer, the upper limit for the resulting ice layer thickness is theoretically modelled. The theory shows very good agreement with the experimental results for all impact conditions. Based on the derived theoretical scaling, a semi-empirical equation is obtained which allows an a priori prediction of the final ice layer thickness resulting from a single drop impact, knowing the impact conditions. This capability is important for the improvement of existing ice accretion models.

The use of high-speed camera technique for observation of soil splash phenomena

2020 ◽  
Author(s):  
Michał Beczek ◽  
Magdalena Ryżak ◽  
Rafał Mazur ◽  
Agata Sochan ◽  
Cezary Polakowski ◽  
...  
Keyword(s):  
High Speed ◽  
Initial Moisture Content ◽  
Soil Surface ◽  
Drop Impact ◽  
Solid Particles ◽  
High Speed Camera ◽  
Water Drops ◽  
Crown Formation ◽  
Raindrop Splash ◽  
The Impact

<p>Soil, i.e. the natural outer layer of the lithosphere and an important component of many ecosystems, may be subjected to various degradation processes dependent on different factors. One of the forms of degradation is water erosion, where the first stage is the splash phenomenon. This process is caused by water drops hitting the soil surface during rainfall, which results in detachment and ejection of splashed material and transport thereof over different distances. The aim of this study was to present the application of the high-speed camera technique for investigations of surface phenomena (effects) influenced by the impact of a single water-drop onto the soil surface.</p><p>The measurements were conducted on types of soil differentiated in terms of texture and variants of initial moisture content, which helped to observe different aspects of the soil splash phenomenon. Water drops with a diameter of 4.2 mm fell on soil samples with various kinetic energy values depending on the height of the drop fall (up to 7m). Phantom Miro M310 high-speed cameras were used to observe the effects of the drop impact. The devices registered images with a speed of 3260 fps (frames per second) at the highest available resolution (1280x800 pixels). The following phenomena were observed: I) ejection of splashed particles (including solid soil particles, water droplets, solid particles within the water sheath); II) crown formation – when the drop impacting onto wet soil surface forces the liquid layer to rise up and form a crown (important for the mode and amount of transferred material); III) micro-crater formation – the deformation of the surface and formation of a shallow pool after the drop impact.          </p><p> </p><p>This work was partly financed from the National Science Centre, Poland; project no. 2018/31/N/ST10/01757.</p><p> </p><p>References:</p><ol><li>Beczek M., Ryżak M., Sochan A., Mazur R., Bieganowski A.: The mass ratio of splashed particles during raindrop splash phenomenon on soil surface. GEODERMA 347, 40-48, 2019</li> <li>Beczek M., Ryżak M., Lamorski K., Sochan A., Mazur R., Bieganowski A.: Application of X-ray computed microtomography to soil craters formed by raindrop splash. Geomorphology 303, 357-361, 2018</li> <li>Beczek M., Ryżak M., Sochan A., Mazur R., Polakowski C., Bieganowski A.: The differences in crown formation during the splash on the thin water layers formed on the saturated soil surface and model surface. PLoS ONE 12, 2017</li> </ol>

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