[AtoHM]

Hi all,
I've come across a strange issue. I am basically simulating water flow into a tank. The inlet is a horizontal rectangular patch. The flow direction should be applied with 45 deg inclination. So I used Cart. Vel. Components to apply it. The total inlet velocity is known from case mass flow and inlet patch area. To have it applied with 45 deg, I apply it multiplied with 1/sqrt(2) in both my desired directions.
Problem is: mass flow in result and monitor is only 1/sqrt(2) times the amount we were going for. The direction however seems to be 45 deg as we wanted.

I looked it up in the modeling guide, where it is stated, that the normal-to-boundary component of the input is ignored. I must be missing something here, but I dont get a) why it is implemented like that and b) how to get my desired mass flow at the inlet.

Any help is very appreciated.

[Gert-Jan]

I don't see the problem. The massflow into your domain equals the integral of the normal velocity * density. So, if your velocity component that is normal to your boundary is reduced by a factor 1/sqrt(2), then the massflow is reduced by that factor as well. In fact, the massflow into the domain is not affected by the components perpendicular to the normal component at all. You could apply a strong swirl, or 100 m/s in the other direction....... it will not affect the amount of mass going into your domain.

So, if you want to obtain the same amount of mass on your inlet, you should not multiply by a factor of 1/sqrt(2). Just leave it as it is. You should just make the other direction equal to the normal direction. Then you have 45°.

[AtoHM]

Thanks, you are right. I was a bit too focused on the vector thing and ignored your first point, that only normal component is actually going through the patch.
Still seems kind of odd to apply it twice ...