# simulating flow in a flume

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March 6, 2013, 05:05
simulating flow in a flume
#1
Member

bird
Join Date: Sep 2012
Posts: 42
Rep Power: 5
Dear all,
Hi, as we can see in the piture, I am simulating flow in a 50m long water flume. The inlet velocity is about 44cm/s, the depth is 50cm. 2500 grids in x direciton is used for 50m long flume and 70 grids in z direciton is used for 70cm in height. After the flow becoming steady, I plot x-velocity in z-direction at about x=35 to 40m, and the outcome is the blue curve. However in experiment the outcome turns out to be the green curve.
So my question is, how could I improve my model?
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March 7, 2013, 04:51
#2
Member

Yi-Lang Chen
Join Date: May 2009
Posts: 58
Rep Power: 8
Quote:
 Originally Posted by pyxbird Dear all, Hi, as we can see in the piture, I am simulating flow in a 50m long water flume. The inlet velocity is about 44cm/s, the depth is 50cm. 2500 grids in x direciton is used for 50m long flume and 70 grids in z direciton is used for 70cm in height. After the flow becoming steady, I plot x-velocity in z-direction at about x=35 to 40m, and the outcome is the blue curve. However in experiment the outcome turns out to be the green curve. So my question is, how could I improve my model?
Dear pyxbird :

You can try to set up "roughness height"

March 7, 2013, 04:54
#3
Member

bird
Join Date: Sep 2012
Posts: 42
Rep Power: 5
Quote:
 Originally Posted by Andy Chen Dear pyxbird : You can try to set up "roughness height"
Where is it? And what's the value I should give to it?

 March 11, 2013, 05:34 #4 Member   Yi-Lang Chen Join Date: May 2009 Posts: 58 Rep Power: 8 geometry-->component-->component properties-->surface properties-->surface roughness you have to set up roughness height at surface roughness, and that Dimensionless is [L]. It was obviously on your results file. your geometry was too smooth so that velocity too fast at bottom. What is material of your flume? You can set about roughness height according to your flume.

March 13, 2013, 07:37
#5
Member

bird
Join Date: Sep 2012
Posts: 42
Rep Power: 5
Quote:
 Originally Posted by Andy Chen geometry-->component-->component properties-->surface properties-->surface roughness you have to set up roughness height at surface roughness, and that Dimensionless is [L]. It was obviously on your results file. your geometry was too smooth so that velocity too fast at bottom. What is material of your flume? You can set about roughness height according to your flume.
I haven't added any component or material in the simulation.
You mean I should set a component at the bottom instead of using wall boundary at Zmin? I have tried to changed the friction coefficient up to -10, but it is useless.
So how about the roughness height? For example if it is glass, what shall the value of roughness height be?

 March 14, 2013, 03:54 #6 Member   Yi-Lang Chen Join Date: May 2009 Posts: 58 Rep Power: 8 If you want to set surface roughness, then you have to add component. Otherwise, it doesn't work. You have to set surface roughness, not friction coefficient. You can refer about fluid mechanics book or search roughness height [ks]. And you'll know what should you need set roughness height about glass material. Are you study hydraulic?

March 18, 2013, 07:22
#7
Member

bird
Join Date: Sep 2012
Posts: 42
Rep Power: 5
Quote:
 Originally Posted by Andy Chen If you want to set surface roughness, then you have to add component. Otherwise, it doesn't work. You have to set surface roughness, not friction coefficient. You can refer about fluid mechanics book or search roughness height [ks]. And you'll know what should you need set roughness height about glass material. Are you study hydraulic?
It does work. Thank you very much, this problem has puzzled me for such a long time. Thanks a lot.

December 25, 2013, 03:37
#8
New Member

Join Date: Dec 2013
Posts: 6
Rep Power: 3
Quote:
 Originally Posted by Andy Chen If you want to set surface roughness, then you have to add component. Otherwise, it doesn't work. You have to set surface roughness, not friction coefficient. You can refer about fluid mechanics book or search roughness height [ks]. And you'll know what should you need set roughness height about glass material. Are you study hydraulic?
hi
I simulate flow in a flume, in analyse results the flow direction change in the middle of the flume, can anyone help me?

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