[priyankap]

Hello everyone,


I have a question related to direction of velocity. shape of my fluid region is given in the figure attached.


The inlet is in the in the x direction, but the pipe has multiple curves in it, so, I am getting confused that in which direction should I define the velocity while putting the initial values and boundary conditions for the velocity (U)? I am currently using the following:

U
{
    internalField   uniform (1.33 0 0);

    boundaryField
    {
        inlet
        {
            type                fixedValue;
            value               uniform (1.33 0 0);
        }

        outlet
        {
            type                zeroGradient;
            
        }

        "fluid_to_box"
        {
            type            noSlip;
        }
    }
}

As you can see in the attached figure, the direction of flow is changing throughout the domain.


So I need to know in which direction should I define my velocity in internalField and at inlet?


Thank you!

[yambanshee]

The direction is always relative to the global co-ordinate system. So for the case of your inlet, the way you described the pipe supports the fact that your inlet condition is correct.

For the internal field, this is mostly used as a initialisation value for the entire domain. In your case, the flow direction varies greatly through the domain, primarily in the up/down direction (y direction? I can't see based on your attached figure), and so I would think specifying a value in the x direction won't help with your simulation's convergence. I would personally rather set the internal field velocity to (0 0 0) or make use of the setFieldsDict if you really want. In the end, it is the cfd code's job to change the value of the internal field based on your boundary conditions, and so only the boundary conditions are 'set in stone'

[ykanani]

Originally Posted by priyankap

Hello everyone,


I have a question related to direction of velocity. shape of my fluid region is given in the figure attached.


The inlet is in the in the x direction, but the pipe has multiple curves in it, so, I am getting confused that in which direction should I define the velocity while putting the initial values and boundary conditions for the velocity (U)? I am currently using the following:

U
{
    internalField   uniform (1.33 0 0);

    boundaryField
    {
        inlet
        {
            type                fixedValue;
            value               uniform (1.33 0 0);
        }

        outlet
        {
            type                zeroGradient;
            
        }

        "fluid_to_box"
        {
            type            noSlip;
        }
    }
}

As you can see in the attached figure, the direction of flow is changing throughout the domain.


So I need to know in which direction should I define my velocity in internalField and at inlet?


Thank you!

Your inlet velocity should be defined such that it is normal to the inlet patch (I guess that is what you want). The internal field is not that important as it is only an initial value, you can even start from (0 0 0).

Regards,
Yousef

[priyankap]

Thank you Yambanshee and Yousef. This solved my problem.

[jherb]

If your flow enters your domain perpendicular to the surface of the inlet you can use the boundary condition surfaceNormalFixedValue. Then you do not need to specify a vector but just the scalar value (be careful with the sign, negative values are entering the domain, positive leaving it).