[mmengineer]

Hello everyone,

i´m using a porous zone in an open channel flow. The porous zone represents a blockage and stretches over the wohle width of the channel. I am feeding the simulation with a quadratic pressure loss function, so i am only defining values for C2/t.

As a control of input vs. output, i defined report files for the volume averaged water height in the porous zone (calculated over volume averaged volume fraction x height of the porous zone). With the volume averaged height an the known discharge, i can calclate the volume averaged velocity in the porous zone.
Additionally i am monitoring the pressure drop caused by the porous zone, via total pressure at the front face minus total pressure at the back face of the porous zone.

When i am calculating the "output" pressure drop function, as pressure drop over volume averaged velocity, i am not getting exactly the same function as i used as input value. I am observing a small drift, as if there were an additional linear part to the actually solely quadratic input function.

Has anyone encountered a similar prol´blem, or does anyone have an idea why this (small) drift occurs?

I am happy for every help i could get.

A graphic with input and observed output functions is attached.

Regards