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Old   March 1, 2015, 12:36
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Hi i m doing a CFD analysis of thermostat valve . My inlet boundary condition is velocity inlet c=1.25m/s . Outlet is pressure outlet .I am using K-epsilon model and simple algorithm.No energy equation. If i activate laminar zone in cell zone conditions then my problem is getting solved. But i have turbulence in my flow. So i gave turbulence and hydraulic diameter in my BC and i deactivated laminar zone and then i get divergence in epsilon. Can anyone help me out ???
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Old   March 1, 2015, 13:44
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Dear Barathwaj,
Turbulent kinetic energy k is basically determined by your turbulent intensity set.
And the dissipation epsilon is determined by both length scale and turbulent kinetic energy.
Since you have had K converged, it might be the problem of length scale: ie, hydraulic diameter.
There could be many reasons for not converging.
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Old   March 1, 2015, 13:53
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I ve given my pipe diameter as my hydraulic diameter. And I also calculated my turbulent intensity as 5% . So is there any mistake in this value
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Old   March 1, 2015, 13:59
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these seem to be right, and how about your mesh quality?
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Old   March 1, 2015, 14:02
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Geometry of the valve is complicated .skewness is very high. I couldnt reduce it.I tried both with fine and medium mesh and also I increased smoothness. Yet I had this error.
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Old   March 1, 2015, 14:03
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Or maybe you can decrease the turbulent intensity if you don't have that large Reynolds number. In my opinion, the Intensity here simply provide an initial guess for your equations to be iterated/solved, it has no effect on your result normally.
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Old   March 1, 2015, 14:05
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Decrease intensity, and if it doesn't work, try to decrease you relaxation factors, although i don't believe this will help you too much.
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Old   March 1, 2015, 14:06
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My Reynolds number is around 180000
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Old   March 1, 2015, 14:07
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WOW! then your intensity is not high...
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Old   March 1, 2015, 14:08
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What should I do??
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Old   March 1, 2015, 14:11
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Try to decease your relaxation factor, and btw, how could you have that high Re with a speed of only 1.25m/s initially? Sorry i have no idea of thermostat valve.
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Old   March 1, 2015, 14:13
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My pipe od is just 0.053 m that's the problem fluent is water dynamic viscosity is also very low . that's why I get such a large Reynolds number
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Old   March 1, 2015, 14:14
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Regarding the relaxation factor should I ve given it as 0.8 . should I reduce it to o.5
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Old   March 1, 2015, 14:17
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Re=density*velocity*D/viscosity=998.2*1.25*0.053/0.01=6625?
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Old   March 1, 2015, 14:18
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I think the default is 0.8? and yes try 0.5.
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Old   March 1, 2015, 14:21
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Viscosity of water is 0.000338 (kg/(m-s))
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Old   March 1, 2015, 14:23
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Sorry, i am wrong with that , but viscosity is 0.001 from what i see, giving turbulent intensity 66250, are you talking about water vapor maybe?
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Old   March 1, 2015, 14:25
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Not really. I need viscosity of water at 84 deg c for my problem
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Old   March 1, 2015, 14:28
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Well, then i can't help more, just try the relaxation.
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Old   March 1, 2015, 14:29
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Okay thanks a lot. I ll tell you the results. Can I get your mail id
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divergence detected, fluent 15, k-e model, turbulence and laminar

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