Movies on Particles in Fluids Simulation

StrouhalsSuzuki.mpg This movie shows the developing of a Karman-Vortex street behind a circular obstacle at a Reynolds-Number of 100. The colors indicate the pressure. The Strouhal-number computed with this code (0.166) is about two- to three digits accurate compared to the literature values (0.164, 文献値,日本流体力学会編. 第2 版流体力学ハンドブック. 丸善, 1998).

SinkingParticleSuzuki.mpg This movie shows a square particle sinking in a viscous fluid without flow. (We choose a square particle, because for granular particles, this will have the "worst" shape for the surrounding flow.) The color indicates the pressure, while the arrows indicate the particle velocity. We tried to maintain the Finite-Element (Friedrichs-Keller)-grid at all costs. The forces on the particle are becoming non-smoth (noisy), but the time-integrator can still deal with the force fluctuations so that a continuous motion results.

SinkingParticleSakai.mpg This movie shows the same setup as before, but with a finer lattice discretization around the particle. It can be seen that the sinking particle introduces convection rolls. The flickering of the colors (pressure) indicates that our spatial discretization is not yet satisfying: In fact, the discretization along the large gradients of the pressure is still too rough, so the pressure shows artificial oscillations. The forces on the particles are nevertheless continuous.

SinkingParticleDrift.mpg This movie shows a particle which is dropped in a flow field which is driven by the flow as long as it is not in full contact with the ground. As a test of the stability, it is ok, but the pressure field is again not satisfying.

gravity20.mpg This movie shows the simulation of a gravity wave with our simulation: The finite elements on the surface are moved according to the velocity of the fluid in the elements, no additional data structures are necessary.