# Free surface is below than expected..results are not good

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November 15, 2009, 18:36
#21
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Glenn Horrocks
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Quote:
 my length scale is 50 mm!
That may well be quite large, but of course a bit meaningless without the rest of the bits to make up relevant non-dimensional number. Do you know the Re, We or any other relevant non-dimensional number for your flow?

Why do you think surface tension is important? It usually is not significant for large length scales.

If you want to make surface tension a function of temperature then obviously you need to model the energy equation. This will add significant complexity and instability to the model, only do this if its contribution is significant.

I recommend you start with constant surface tension (and isothermal) before tackling the more difficult varying temperature/surface tension simulation.

The reference in the documentation describes how the compressive discretisation scheme find the free surface. Also I think there a description of the surface tension approach in the documentation.

 November 16, 2009, 09:45 #22 New Member   Join Date: Jun 2009 Posts: 13 Rep Power: 10 hi are you sure that i need the energy equation? it is q=n*delta(h)? i have a laminar flow so i think it is RE as non-dimension number. how did the solver know that i actually declared the surface tension by the expressions? the surface tension-curve as function of the temperature is that what i have to implement!so itīs very important to me to know how the surface tension is changing during the flow. i have first of all a water film on a platt . this platt has 2 different temperatures(2 bottoms),my flow is laminar. later i will modelling a polymersolution!

 November 16, 2009, 19:03 #23 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,309 Rep Power: 110 You don't know what the energy equation is, you don't know what the Re number is.... Sounds like you need to learn some basic fluid mechanics. I would forget about modelling surface tension and polymerisation until you know the basics.

 April 8, 2011, 00:17 different result #24 New Member   Iqbal, Muhammad Join Date: Apr 2011 Posts: 3 Rep Power: 8 dear all,, what do you think,, i ran free surface flow on ship at 7 knot and 9 knot,, and the result of force x on ship on 7 knot in negative but on 9 knot is positive.. which is true..?? please answer,, and thanks before..

 April 8, 2011, 00:41 #25 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,309 Rep Power: 110 Probably neither. Please do not hijack threads. Start a new thread for a new question.

 Tags free surface, unsatisfactory results

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