MCEN 4151
Flow Visualization
Team Vis 1: Teamwork Makes The Steam Work
Robbie Cooper
MCEN 4151: Flow Visualization
Mechanical Engineering, University of Colorado Boulder
- Introduction
This photo was captured to show how turbulent flow behaves. It shows fog rising out of a fog machine. In this experiment, we tested different lighting angles, amount of fog released, and camera angles. Inspiration and motivation came from flat lasers cutting smoke and showing spirals and boundaries of the flow. In our experiment it was a little harder to capture since our laser ran out of battery and had to use headlands with color filters.
- Experimental Setup
Figure 1
The set up for this experiment was really tedious. TO take pictures of clouds, smoke, and fog you need a lot of light and a dark background. Depicted in the image above is how many hands were used to capture our pictures. In this shot, Cole(on the right) is holding the headlamp and turning on the fog machine, Kendall(in the middle) is holding the black background and other headlamps for light, and Lana (on the right) is taking pictures on her camera.
- Flow Phenomena
What’s being demonstrated in this image is turbulent flow and pressure. The fog machine turns liquid glycol to vapor and when the machine does this, the vapor expands and pushes the gas out the machine. This particular machine creates a lot of fog very fast so it pushes out the fog at a fast rate for a small volume which creates turbulence in the flow. The fog goes up because the shape of the chamber where the fog exits is a cube with an open top. It will expand upward and outward because the molecules bounce off each other and head in different directions.
- Flow Visualization Technique
For this experiment we used a 400W fog machine that blows flat fog. The machine also has a hatch on the top which allows for the fog to float out and expand into the open space. Setting up with the open hatch provided us the best results for capturing the shape of the fog. A difficult part of working with this machine was controlling the exit velocity of the fog, it would spit the fog out of the normal nozzle at roughly 1.5m/s, where alternatively out the top it would be a more steady 0.5m/s.
The channel that the fog was flowing through is 5.5x5.5 inches and had an exit velocity of about 0.5 m/s. So about but less than 15.125 m3/s of cloud mass was being at a time. This made the experiment pretty hard, the flow was really fast so the clouds would exit the frame of the picture within 5 seconds.
- Photographic Technique
For my image I used a Canon EOS 70D with a 18-55mm lens size. The lighting we had in this shoot was around 400 lumens, our three iPhone flashlights are around 120 lumens and the two headlamps we used added a little more light. We used high shutter speeds so that we could capture the quick turbulent movement of the fog. The camera settings were: apertature: 6, exposure time: 1/150, ISO speed: 400, and F-number: f/8 and focal length: 27mm. The criteria for the picture was bright enough to see the color and cloud, but dark enough to see contrast and shape in the cloud. The camera was 2.25ft away from the fog machine and my camera had a focal length of 27mm.
Figure 2: Image before Editing
Figure 3: Image after darktable editing
- Conclusion
What I liked about this photo was the color difference in the top and bottom halves, as well the mixing of color in the thicker part of the cloud. Particularly the blue part of the cloud is my favorite because it looks energetic and misty like a thundercloud. Personally I feel like this experiment failed because the shape and complexity of the cloud was lost in the darkness, and this fog machine made it difficult to capture the result our group was looking for. If I were to change anything about this experiment, I would have the fog machine shoot fog slower and have a working flat beam laser.
- References
(1) Callen, Jenny. “Fogging Machine: What Is It, Uses, & How It Works.” JENNYCHEM, 31 Aug. 2021, https://www.jennychem.com/blogs/news/guide-on-fogging-machine.