Accurate free surface capturing

The elbe code uses a coupled LBM-VOF model for the simulation of free surface flows. The hydrodynamics in the air phase are not resolved but represented by proper kinematic and dynamic boundary conditions at the phase interface.

Exemplarily, a three-dimensional dambreak experiment (conducted by the MARIN group, www) is simulated with a two-dimensional LBM-VOF model. The initial water column collapses and finally hits a scale model of a container on the deck of a ship. Both the water heights and pressure signals have been measured during the experiment and our numerical simulation, and very good agreement was found.

Two-dimensional dambreak simulation, Silke Gralher.

Similar VOF models are available in 3D as well. In the following three-dimensional simulation, the flow past a weir is adressed. The subcritial inflow switches to a supercritical state on the back of the weir - the flow is accelerated and the water height drops. Subsequently, behind the weir, a hydraulic jump occurs and the flow field changes back to a subcritial state. The predicted flow velocities and water heights on the back of the weir and in the outflow region agree very well with the ones predicted by Bernoulli's theorem. Moreover, the 3D simulation gives a very detailed insight into the flow dynamics inside the hydraulic jump, including air eintrainment, backflow and mixing. The computational time for this scenario was less than 10 minutes.

Simulation of the flow past a weir (WES profile).