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Old   April 30, 2014, 16:12
Default velocity magnitude and direction!!
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Astio Lamar
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Hello everybody.

I have a problem to set the velocity inlet boundary condition in form of "velocity magnitude and direction".

I want to introduce 2m3/s to my domain. So by having the inlet area I did the following:
2/inlet area = inlet velocity.
When this value assigned in the form and velocity, normal to boundary, I got the correct volume flow rate at the inlet.
But since the inlet velocity is not normal to boundary, I set the direction:

X-component of Flow Direction: 0.5627
Y-component of Flow Direction: 0.8267

then I got 1.65 m3/s in the inlet!!

Does anyone know what is the problem? why it is so? and what is the solution?
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Old   April 30, 2014, 17:44
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Behrooz Jamshidi
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According to your data i think your inlet face normal vector is in y direction.
When you say for normal velocity it is correct but for non normal velocity its not, this shows that Q/inlet area=inlet velocity is not a scalar equation its a vectorial equation.
For having 2m3/hr at face, you should set a volume flow rate so that its y (normal vector direction of your face) component equals 2m3/hr.
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Old   May 1, 2014, 05:14
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As the person before me suggested, the x,y,z-component of flow direction are the scalar components of the flow vector. Each of those components carry the units (default is m/s).

Depending on which plane your inlet lies in, you need to specify the right x or y component velocity to get the desired volumetric flowrate. And then specify the other component to get the desired direction.
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Old   May 2, 2014, 03:12
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Astio Lamar
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Hello and thanks for your reply.

@ LuckyTran: Would you please advice how can I set the correct x and z component of velocity to have 2m3/s flow rate on the inlet? degree = 30

Last edited by asal; May 6, 2014 at 11:31.
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Old   June 20, 2017, 17:59
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Hello all,

I have the same problem, Asal. did you fix the problem?

Consider the following example:
Inlet is normal to -Y with total area of 0.1 m2.
1 m3/s should be imposed to the inlet with 65-degree deviation from the inlet normal.

In this case:

velocity = 1 [m3/s]/0.1 [m2]= 10 [m/s]


y-component = 10*cos(65)
z-component = 10*sin(65)

However, this will not give the desired volume flow rate (1 m3/s)

Can anyone explain this?

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