[AMR96]

Hello,

I am trying to simulate air flow in a curved tunnel over a car and have some questions regarding the boundary condition selection. Since the flow in a curved path is not symmetric and the velocity is higher on the outside as a result the pressure distribution at the outlet is not uniform and there is a gradient.

In my first attempts of the simulation I made the assumption that pressure is equal at the atmospheric pressure at the outlet and selected the standard fixedValue BC for the outlet however the pressure residual doesn't decrease below 10^-2 magnitude unless I change the URF in which case the best residual I get is around 10^-3.

I did some digging around the forum and found that maybe the pressureinletoutletVelocity BC could help. This is what I set up as my boundary conditions:

For pressure

inlet
{
    type zeroGradient;
}

outlet
{
    type totalPressure;
    rho none;
    p0 uniform 0;
    value uniform 0;
}

For U:

outlet
{
    type pressureInletOutletVelocity;
    value uniform (0 0 0);
}

Another method that I have found was to simulate with fixedValue condition at the outlet and extract the pressure profile of the inlet then plot it as a function of radius and then find the equation that fits the curve. Afterwards, using groovyBC, I would define the outlet pressure boundary condition with the new equation.

Now, the questions:
1. For the method with pressureInletOutletVelocity, I would like to know if this boundary condition can help achieve what I want to do or should I use the method with a custom boundary condition?

2. In the method with the custom boundary condition, the equation for the plot would be a linear equation of the type p(x)=ax+b. In this case would defining the pressure outlet boundary as the following be correct?

type groovyBC;
variables (''xp=pos(x) .x'');
valueExpression ''a*xp+b'';
value uniform 0;

I have also included a picture of the domain for reference. The flow enters from the nearside and is along the x-axis and z-axis.


Many thanks in advance for any guidance!