Yue, Nick, and I are working on making a submission for the Gallery of Fluid Motion, a part of the upcoming meeting of APS Division of Fluid Dynamics. The name is taken after the famous album of photographs of fluid flow visualization collected and compiled by Milton van Dyke.
We thought the case of many soft, elastic rods moving through fluid would be interesting to look into. From intuition, we all can conjure up an image of a rod falling down in a tank of fluid. When it is long, thin and soft, its middle tends to sack first while the tips lag behind, forming an upward curve (a smile). But what happens when lots of them fall together? And what happens if some of them float while the others sink? We are simulating these scenarios using the computational codes I developed with Nick (details in a previous post).
Here is a sneak peak, well, two sneak peaks. Yue and Nick are working on polishing the videos, so the finished version is yet to come.
When many randomly placed rods are falling together, instead of the individual rod developing the smiley shape, the middle of the collection of rods as a whole sacks first. This is due to the lower drag in the middle of the domain (closer to the walls, viscous resistance is higher).
I also played around with the simultaneous floating and sinking case. The top rods are heavier, while the bottom rods lighter. The heavier and the lighter rods are perpendicular in orientation. As the rods settle or float, they slip to the sides of the domain to pass one another.