Cavitation
Cavitation is an interesting physical phenomenon that involves bubble growth and phase change through dropping pressure in a liquid. These simulations are part of a study evaluating dynamic stall in a cavitating flow (https://arc.aiaa.org/doi/abs/10.2514/6.2006-1279). On top of this, we are also developing novel models (https://asmedigitalcollection.asme.org/fluidsengineering/article-abstract/141/4/041301/367359) as well as understanding how cavitation models behave (https://www.semanticscholar.org/paper/A-unified-homogenous-multiphase-CFD-model-for-Kinzel-Lindau/0ec0af4da924e7b67b8b7f84ad6bfc7b740e9e61).
Early eddy-resolving simulations of cavitating flow:
Probably a more interesting avenue is work with understanding cavitation inception. This is what we are currently pushing!
Granular Flow
Granular flow involves modeling pa flow laden with particulate. This is not easy! In the following animation, results for a mixing vessel using a puslating jet are displayed. Here the mixture includes a liquid, gas, and 5 different solids. In these simulations, each of these “7 phases” have different velocities and the solids are both settled (like a porous bed) and lofted (like a disperse multiphase flow). We really pushed CFD to the limits here. In the end, CFD had about the same error bar as experiments (the goal of all CFD).
Compressible Multiphase Flow
If you think any of the previous CFD problems are tough, try these ones! Compressible multiphase is extremely difficult but is where CFAL lives. Here are a few examples of some of our recent works:
High-speed gas jets released underwater with work summarized in:
- https://arc.aiaa.org/doi/abs/10.2514/6.2016-4253
- https://asmedigitalcollection.asme.org/FEDSM/proceedings-abstract/FEDSM2017/58066/V01CT14A009/234262
- https://etda.libraries.psu.edu/catalog/14386maf5524
Cavitation Induced by Underwater Explosions: Now this is cool. Explosions lead to high pressures, right? So when these pressure reflect off a free surface, the pressure drops and actually leads to cavitation. Not only does this blow you mind, it also blows up microbubbles and creates bubbles clouds. Cool stuff highlighted below:
- https://etda.libraries.psu.edu/catalog/zs25x844t
Cavitation can also occur from bubble expansion. This relates to damage on marine vehicles. This is a simulation highlighting local loads from a 20 micron bubble exposed to a low pressure. Note that the pressure oscillations, over a roughly 20 micron radius, are 1 atmosphere! This is a huge load that leads to pitting and erosion.
We are also exploring droplets interacting with vehicles at very high speeds. A sample of this work is provided in the figure below. This is the leading edge of a Mach 6 airfoil and the impact of a 20 micron droplet as it processes through the shock. We are finding really amazing things, such as the potential of the droplet to cavitate.
Additional studies are being carried out by Ph.D. Student, Caroline Anderson. See a draft of her AIAA Aviation talk here:
Free-Surface Flows
Ever thought about fluid sloshing when you stop a tanker half full of liquid? Here is a simulation elucidating the resulting complex slosh loading. These simulations indicate many scales and a complex interaction. In this work we extended this to very simple, real-time models, hence, reduced complex physics to usable models!