# Entrance Length in Laminar Pipe Flow

 Register Blogs Members List Search Today's Posts Mark Forums Read

 March 28, 2018, 05:15 Entrance Length in Laminar Pipe Flow #1 New Member   djr4cfd Join Date: Jan 2018 Posts: 13 Rep Power: 8 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.

 March 28, 2018, 06:17 #2 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15 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. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

 March 28, 2018, 07:53 #3 New Member   djr4cfd Join Date: Jan 2018 Posts: 13 Rep Power: 8 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??

 March 28, 2018, 08:11 #4 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15 This looks good. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

March 28, 2018, 08:25
#5
Member

Hosein
Join Date: Nov 2011
Location: Germany
Posts: 93
Rep Power: 14
Quote:
 Originally Posted by djr4cfd 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.

 March 28, 2018, 09:07 #6 New Member   djr4cfd Join Date: Jan 2018 Posts: 13 Rep Power: 8 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.