Two drops are interacting—one has fallen into the water and has recoiled upwards. The other drop has smashed into the first one. They form an umbrella-like pattern. Report
By Max Scrimgeour for 2016 Get Wet
By Sierra Castillo, for Get Wet 2016.
Suspended splash, created literally by hand, distorts beautiful mountain background in Phelps Lake in Grand Teton National Park, WY.
Get Wet report
By Sierra Castillo for Flow Visualization, MCEN 4151
Flow Visualization is dedicated to producing images and videos of fluid phenomenon. The purpose of the Get Wet image, as our first assignment, is to experiment with different flow phenomena and to get practice producing images of fluids. For my submission, I wanted to demonstrate the physics of water when a splash is induced. Using a GoPro, I swam out into a lake and filmed myself splashing my hand/arms in the water.
For this image, there was no technical apparatus used to produce the image. Quite simply, I swam into the lake and began treading water. I positioned my camera close to the water and in line with my body. Once it was positioned as square and level as possible, I swung my arm over my head and into the view of the camera. Once it hit the water, the splash commenced and finished within the span of a few seconds. Later, I went through the video frame by frame, and exported a still image of the splash. It would be impossible to exactly reproduce this image, but capturing a similar one would be fairly simple with a waterproof camera that has video capabilities. A sketch of the positioning of the camera and my arm is shown below in Figures 1 and 2.
Figure 1: Top View of position of my body in the lake.
Figure 2: Front View of position of my body in the lake.
Though the process is quite simple, the physics of the image are quite interesting. The image was captured at the end of the splash. If this were a single drop of water, this would be the moment of the Worthington Jet. By this, I mean that the air cavity created when my arm hit the surface of the water was refilled rapidly by water. This in turn, propelled a quantity of water into the air. Due to the surface tension acting on these propelled particles, the sheet of water was created. There is a spot on this sheet that appears to have been hit by a stray particle producing ripples within the sheet. This is an interesting addition to the image and gives some insight into the chaos that commenced after splashing the water. Another interesting aspect of the image is the fingers that form on the edges of the flow.
The camera used to capture the image is the GoPro Hero 4. Unfortunately, the GoPro Hero 4 lineup does not have metadata available, so I can only give information about the settings I changed. The ISO was set to 1600. The white balance was set to 5500K. Finally, the EV compensation was set to 0. The rest of the settings are automatically changed by the camera. The sheet of water is about a foot in length. The distance from the lens to the splash is about 1.5’. The focal length is about 21.9mm for this camera (medium FOV). For post processing, I simply increased the contrast of the image and darkened the shadows a little bit in Photoshop. My intent in these edits was to emphasize the details in the various nooks and crannies in the flow that were lost in the original image. The original image can be seen in Figure 3, below . The edited version can be seen above.
Figure 3: Original, Unedited Still
I like that the image is chaotic and fuzzy in one corner, while the other corner is calm and sharp. The sheet of water is very clear. I like that there is one droplet that bounced off of this sheet and has little ripples in it. It is an interesting “blemish” on the sheet. I also like the various fingers that extend from the sheet of water. Finally, I really enjoyed capturing the image. It isn’t often that a technical engineering course gives you the opportunity to play in the water. It was fun messing around with different splash techniques and going through the footage to see what was actually happening. I wish that I could have captured more of the background so that the distortion of the background has some context. It would have been nice to see the difference between the water-distorted and actual mountain background. I also wish that the lighting was a little better. I think if I had been able to catch the image at a later time in the day when the sun was more behind me, the reflections could have been really interesting. It would also have helped if the clouds weren’t blocking the sun as much as they were. Overall, I am happy with the outcome, especially since it wasn’t a “controlled” experiment so much as it was a test of the spontaneity in the splashing water.
Gekle, Stephan, and Jose Manuel Gordillo. “Generation and Breakup of Worthington Jets After Cavity Collapse.” Journal of Fluid Mechanics (2010): 1-3.Research Gate. Web. 27 Sept. 2016.
By Katie Yarnell for Get Wet 2016
Water droplet splashes into a deep pool of water, creating a crown and distorting the reflection of the colorful background.
The first project was to take a picture that had to do with flow visualizations; it was titled ‘Get Wet’. The criteria was very open to the photographer and left everything to their creativity and interests. This photo is a droplet of water hitting a shallow bucket of water, which showed the crowning effect that occurs when a droplet hits a pool of still standing water. This was the phenomenon the photographer wanted to achieve. The photographer also wanted to show reflectivity of the water by multiple flashes and an interesting background.
Photos of the apparatus are shown in Figure 1 below. A dropping devise was created for this purpose specifically. There were two rods attached orthogonally to one another, so the photographer could adjust both height and horizontal length. Attached to the horizontal bars was a dropper apparatus, made from pipe fittings and an eyedropper. Which would drop droplets of water fast or slow depending on the setting.
Figure 1 Setup
The camera setup was fairly simple, using a 105 micro ‘macro’ lens and a tripod also with three synchronized flashes. An SB 600 Commander controlled the flashes; two of the flashes were pointed at the background, which was a grey glittery paper, and the other flash was pointed at the location of the droplet impact to freeze the motion. The camera was set on Aperture priority and had an ISO of 200 and an aptitude of F-25 and a shutter speed of 1/60th.
The phenomenon of water dropping into a pool of water can show three different effects: the drop bounces and then floats to the pool’s surface, the drop blends into the pool, or the drop splashes forming a crown or crater. The density, the velocity, surface tension, and the diameter of the droplet, in forms of the Weber number, determine which splash will occur. The Webber equation is We = roe*d*v^2/sigma.
When the Weber number is greater than ~84, the impact creates a crown or a crater. Whether a photograph is of a crown splash or a crater splash depends on when the photo is taken, a crown is developed first, then forms into a crater.
The visual technique used was a flash to freeze the motion, displaying a crisp image of a moving object. Also, for a visual flare, a glittered piece of paper was used as a background to add an artistic view. With two flashes pointing at the background with red and blue color gels over the flashes, the colorful reflection of the water was obtained.
The photographer wanted a large depth of field. A flash was used to freeze the motion and get a very focused image. A macro lens was used to get a close view of what was happening in this phenomenon. The image was edited slightly; a cropping of the image was done to get an even closer view than the macro lens could provide. Also, the photographer adjusted the brightness of the image slightly to make the colors stand out more. The camera was set on Aperture priority and had an ISO of 200 and an aptitude of F-25 and a shutter speed of 1/60th.
The image shows the crowning effect that occurs when a droplet hit a pool of water. The reflection of the crown’s reflection in water is very crisp. The colors are patriotic and visually appealing. An interesting improvement would be attempting a double drop interference picture, though that will be harder to achieve. The hardest part was choosing which photo to use because of the variety droplet effects, figure 2 shows other images taken during the photo-shoot.
Figure 2 Other drop photos
By Tianzhu Fan, for Get Wet 2016
A stone falling into a cup of water creates a splash on the liquid free surface. 09/12/2016
More information: TianzhuFanSep27,2016500PMFlowVisReport1
By Stephanie Mora for Get Wet 2016
A Worthington jet is formed when a droplet falls with enough velocity on a liquid surface (Inglis-Arkell 2015). The droplet creates a crater in the liquid surface and from the center of that crater protrudes a central jet and with enough energy the jet will pinch off and send more droplets upward (Inglis-Arkell 2015). This is the main phenomena I was trying to capture in my Get Wet image, but on top of that, I wanted to capture another droplet hitting that Jet and creating a crown. I was only able to capture as good of an image as I did thanks to an apparatus created by Kyle Walters and Kyle Hollis and a Bluetooth app called dropControllerBT designed by Martyn Currey.
The apparatus they built stood on two metal legs and could have up to three horizontal bars attached between the legs. On any one of the horizontal bars (preferably the highest one) you could then attach 3 liquid containers, each having a tube connected to a dripper. The drippers would be fixed on one of the 2 lower bars. Positioned below the apparatus was a basin of water, approximately a foot and a half in length, 8 inches wide and 4 inches deep. Directly in front of the apparatus was a camera on a tripod which was connected to a circuit box also built by Kyle and Kyle. The circuit box was connected to the drippers and two flashes that were placed on the left and right side of the basin. Everything connected to the circuit box was controlled by the dropControllerBT app. The app allows you to control the opening of each valve, drop start time (in milliseconds), size of drop (controlled by how long valve is open), time in ms when the flash will go off, and the time in ms when the camera will go off (Currey 2016). All of these settings could be customized differently for each valve.
In our trials we noticed that tilting the valves at an angle seemed to cause the Worthington Jet to come back up at an angle. When the second droplet was dropped it hit the middle of the jet as opposed to the top, creating a crown over the middle of it. Through the crown you can still see the jet and how it extends taller than the crown. On the tips of the crown you can see where droplets are being pinched off and extending outward.
In order to bring emphasis and aesthetic appeal to the droplet, we used purple food dye for the droplets. The basin of water did not have any dye in it. To control light we had two external flashes with just white light. In other trials, we had put red and blue filters on each flash, but for this image, the flash did not have a filter. In the room we were in, we had the normal ceiling lights on as well.
Because I did not have the proper cable to connect my small Canon PowerShot SX260 HS to the circuit box, I used their Nikon D700. The camera was placed about 7 inches from the basin, positioned so you could not see any borders of the basin, just the pool of water. We exclusively relied on external flash and lighting. The f-stop used was f/22, an ISO of 400 with a ½ second exposure and the focal length was 105 mm. As I mentioned earlier, these settings produced an image that was too bright and looked a bit washed, especially the purple. This was not our intention, we were playing around with settings and this happened to be the set that actually captured a beautiful drop collision. To add vibrancy back to the photo, I used Gimp to increase contrast and used the burn tool around the droplet collision to bring out the purple. I also cropped the photo to make the focus more central on the droplet collision and remove other distracting boundaries. From previous trials, there were a few droplets on the stuck on the backdrop, which I removed using the clone tool.
My favorite part about this image is the aesthetics of the drop collision. Also, how the crown is transparent and the jet below can be seen. I love the contrast of the purple with the black and white surrounding it. I also love the contrast between the calm ripples and the crown that is spreading out in different directions. I believe that the physics are very well and clearly shown in this image. Neither I, nor the two Kyles understood exactly why the drop was coming up at an angle, because even when we did straighten the angle of the valve, it still came up at a left tilted angle. But this ended up working in our favor. As a non-engineering student, the only improvements I could think of would be incorporating more colors. I would want to drop different colors onto each other and try to capture the blending of those dyes in the droplets. Another idea I would want to do would be having multiple droplets fall side by side, in different colors, and then try to capture 2 or 3 droplet collisions at the same time. The precise controls allowed by the app we used would make it possible to capture such an image.
Currey, M. (n.d.). DropController Bluetooth. Retrieved September 26, 2016, from http://www.dropcontroller.com/dropcontrollerbt/
Inglis-Arkell, E. (2015, June 11). A Rare Look Inside The Formation Of A “Worthington Jet” Of Water. Retrieved September 26, 2016, from http://io9.gizmodo.com/a-rare-look-inside-the-formation-of-a-worthington-jet-1710712711
A Worthington jet resembling an apple (manzana) has formed from colored milk being dropped into a pool of differently colored milk.
By Harrison Lien, for Get Wet 2016
A Worthington jet is a phenomenon in fluid flow that occurs after a droplet of a fluid hits the surface of another fluid that is relatively deep. Initially, when a droplet hits a surface, it creates a crater in the surface, and then a crown shape is made from the surface fluid around the crater. While the crater is still in shape but as the crown has fallen from its peak height, a Worthington Jet rises from the center of the crater. Different techniques can be used to analyze the fluid flow beyond the general shapes created from a droplet hitting a surface of a deep liquid.
This photograph demonstrates some different techniques that can be applied to the study of such a flow. The photo depicts a Worthington jet produced from colored milk hitting a pool of differently colored milk. Milk was released, one drop at a time, into the pool of milk from a height of 3 feet from the surface. The saucer that was used was 3.97 inches in diameter on the outside of the dish, and a depth of 0.51 inches from the bottom at the center to the top of the rim of the dish, and the inside edges had a gentle curve to them, going from the rim to a flat circle of diameter 0.98 inches at the bottom. The photograph was taken with a Nikon D3300, with a focal length of 200 mm, an aperture of f/5.6, a shutter speed of 1/640 seconds, and an ISO of 400.
The surface was initially milk with intentionally poorly mixed red and yellow food dye at the surface. The milk dropped into the surface was dyed with blue food dye. Several drops had been dropped onto the surface, prior to this photo, as seen by green areas on the surface – including the base of the jet. It can be observed from the droplets that have separated from the jet, that some of the original blue milk from the impact droplet have not mixed with the milk on the surface, and retain their true blue coloration. It is interesting to note the angle at which the jet is escaping, as most Worthington jets go straight up from the surface. This angling could be due to an unintentional initial horizontal droplet velocity. As part of a series of photographs like this one, it can be observed with consistency that the Worthington jets always seemed to lean over in the direction of the side of the dish in which they were closest to; jets formed in the center went straight up, and ones on the sides were bent toward their respective side. This observation introduces a new hypothesis: perhaps the curvature at the bottom of the relatively shallow dish changes the jet direction: more careful testing and photography could lead to an answer.
In the photograph, there is also some motion blur that is visible, and perhaps even a little distracting from the clarity of the photograph. While this decreases from the artistic value of the photograph, a measurement of this motion blur can be used in combination with the shutter speed to determine the average velocity of a flying droplet during that brief instant. Some caution should be used with this technique, because this type of measurement cannot measure jet motion along the axis of the lens of the camera.
Although this photo depicts some techniques that could be used for analysis, there are also some features of this photograph that are less useful for the scientific method and more employed for artistic value. The first example of this would be the coloring: the surface could have been better mixed and pure and free from color contamination of other tests. With this in play, one could use the color mixing of the base of the jet to determine the speed of fluid mixing in the surface as the jet is formed.
With such a high speed photo, some photographic sacrifices needed to be made to produce a quality photo, given the lighting conditions. The apparatus was lit up using a 1200 lumen light, focused at the saucer 2 feet away. Even with this bright light, the photo settings were a little lacking, the shutter speed could have been higher to make the photo crisper. Given the focal length and the size limitations of the lens being used, the aperture was already at its limit, at f/5.6: parts of the surface are a little out of focus, but this is seen as acceptable, considering the flow being showcased is within the focal range, and this depth of field adds a little bit of an artistic aspect to the photo. The next thing that could account for the exposure was the ISO. An ISO of 400 makes this picture clear of grain, and perhaps an exchange of light grain for motion clarity could be a necessary trade-off for artistic merit.