[cristopf]

Hi everybody,

I hope anybody can help me out with my case. I´ve got a pipe with an orifice in it. Inlet is on the left and outlet on the right side. I have a turbulence air flow solving with simple foam and want to calculate the pressure drop between Inlet and Outlet.
Inlet:
internalField uniform (0 0 0);

boundaryField
{
inlet_solid
{
type fixedValue;
value uniform (4.63 0 0);
}

outlet_solid
{
type zeroGradient;
}

walls_solid
{
type fixedValue;
value uniform (0 0 0);
}

Outlet:
internalField uniform 0;

boundaryField
{
inlet_solid
{
type zeroGradient;
}

outlet_solid
{
type fixedValue;
value uniform 0;
}

walls_solid
{
type zeroGradient;
}

two cases (attached pictures):
1. short pipe
2. the second pipe is longer after the orifice

The problem is that I get a fewer pressure drop for the longer pipe.
short pipe: dp=63.5 Pa
long pipe: dp=53.5 Pa

short pipe: I assume that the problem is the boundary condition p=0 at the outlet. Perhaps that condition conflicts with the "chaotic" flow profile at the outlet.

long pipe: in that case the flow at the outlet "calmed down". (so I think value of pressure drop more plausible for that case)

How can I change the boundary conditions to get a more accurate value for the pressure drop for the short pipe (if that´s the reason)?
I thought about to work with the type calculated for the pressure at the outlet