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Entrance Length in Laminar Pipe Flow

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Old   March 28, 2018, 05:15
Default Entrance Length in Laminar Pipe Flow
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Dear Foamers,

I just started learning OpenFOAM and I thought of simulating the basic problem of fluid flow through a pipe. I made a 2D mesh with a width of 1m and a length of 10m and simulated the flow using simpleFoam. I understand that the entrance length (development length) can be found by measuring the distance from the pipe inlet to the point where the velocity in the axial direction becomes constant. But in my case, the velocity keeps on increasing throughout the length of the pipe. Why is that happening? Is there any other way to find the development length??

Thank you in advance.
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Old   March 28, 2018, 06:17
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I think you mixed something.

The inlet length is the one it need to homogenize the velocity distribution. The mean velocity cannot increase in such a pipe. Please check your b.c.
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Old   March 28, 2018, 07:53
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Thank you very much for responding. The boundary conditions are as follows:
Velocity:

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

inlet
{
type fixedValue;
value uniform (4.53 0 0);
}
outlet
{
type zeroGradient;
}



Pressure:


pipeWall
{
type zeroGradient;
}

inlet
{
type zeroGradient;
}
outlet
{
type fixedValue;
value uniform 0;
}

Is this right??
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Old   March 28, 2018, 08:11
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This looks good.
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Old   March 28, 2018, 08:25
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Quote:
Originally Posted by djr4cfd View Post
Thank you very much for responding. The boundary conditions are as follows:
Velocity:

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

inlet
{
type fixedValue;
value uniform (4.53 0 0);
}
outlet
{
type zeroGradient;
}



Pressure:


pipeWall
{
type zeroGradient;
}

inlet
{
type zeroGradient;
}
outlet
{
type fixedValue;
value uniform 0;
}

Is this right??
Hey there,

Your boundary conditions are fine for the moment. But based on your information you will need ~57.53 meters to reach to fully developed condition. You may take a look at here "https://www.engineeringtoolbox.com/entrance-length-flow-d_615.html" to calculate your development length.
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Old   March 28, 2018, 09:07
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Thank you piu58 and einstein_zee. As einstein_zee pointed out, my velocity was very high. I corrected it and now it works well. I appreciate you for finding time to respond to my silly question. Thank you very much.
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