open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

we are simulating the flow trough a spillway with a stilling basin downstream. Goal is to determine the spillway capacity for different discharges.
With the hydrostatic version oscillations appear at the location of the hydraulic jump with no steady solution.
Using the non-hydrostatic version we get a steady flow field everywhere and we are very happy about that because we match very well the weir capacity measured in a physical model.

So my question: is there an explanation why the non-hydrostatic version is superior for such a case?
I would say: actually in the spillway area the pressure distribution over the vertical isn't hydrostatic, so the non-hydrostatic version is also the right one to use.. but this is merely a weak argument?

For any hints I would be very glad!

Clemens

Hello,

I see two explanations:

1) the vertical velocity with hydrostatic assumption is only a cosmetic by-product of horizontal velocities, obtained with the continuity equation and used only for drawing pictures (there is one however for advection in the transformed mesh, but also obtained with the continuity), it is not so good if the vertical velocity is not so small...

2) the hydrostatic assumption is wrong on weirs, and the theory leads to a unique capacity of the weir, independently on the shape of the weir, whereas all hydraulic handbooks will give you different values function of the weir shape. This is because the vertical velocity is neglected.

The latter is a strong argument...

With best regards,

Jean-Michel Hervouet