[TWaung]

Hello,

I am attempting to model a flume tank (rectangular channel with free surface flow), with a wall and an actuator disk. Basically a dam with a large turbine. The attached images show a side view of the domain, with the white rectangle representing the wall, and the rectangular outline below the wall representing the extents of the actuator disk.

I am finding that initially, the water surface looks like the first image. Smooth, with no bubbles or gaps on the upstream side of the turbine. However, after running the simulation for a long time in order for the velocity through the actuator disk to reach a steady value, these bubbles/air gaps start appearing in the free surface upstream of the turbine (seen in the second image). This behaviour has also shown up even if I round the edges of the barrage.

I am primarily interested in the head difference across the wall, so this is a problem for me.

Does anyone have any idea what is going on?

The details of the sim are provided below:
Domain: 3D rectangular channel with a wall and actuator disk

Inlet BC: Mass flow inlet for water phase
Outlet BC: Pressure outlet with user function defining hydrostatic pressure
Initial Water level: Defined using a field function
Tank side walls: symmetry planes

Turbulence Model: k-epsilon

Thanks for any suggestions!