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 March 1, 2005, 14:10 questions about V2F viscous model #1 miguel Guest   Posts: n/a Hi to all I have seen at www.turbulentflow.com some interesting information on V2F viscous model. As I am working with bluff bodies, I think this model might be interesting. But I donīt know anything about it. How can it be used? Is it an upgrade for regular Fluent 6.0 or 6.1???? I am interested as the results seem to be better than regular K-e models. Anyone can help? Miguel

 March 1, 2005, 15:29 Re: questions about V2F viscous model #3 miguel Guest   Posts: n/a Thanks Jason I will have a go at it. As I am trying to model bluff bodies with not very good result I will thank you if you could answer some questions. At the moment I am working in 2d.I have done quite a good mesh (skew<0.04) and I have tried some viscous models. -Spalart allmaras: works well with long bluff bodies (length=4R; width=R) but oscilates with short ones(lenght=2R) -K-e standard with enhanced wall treatment: works average with long bluff bodies (length=4R; width=R) and average with short ones(lenght=2R) -K-e realizable with enhanced wall treatment: diverges with long bluff bodies -K-e RNG with enhanced wall treatment: diverges with long bluff bodies All have been tried with the same mesh with an Y+<1, a velocity inlet of 5m/s and a pressure outlet of 0, with operating pressure of 0. Which do you think is the most suitable model for 2d? and for 3d? Thanks: Miguel

 March 2, 2005, 13:29 Re: questions about V2F viscous model #5 pieizquierdo (miguel) Guest   Posts: n/a Jason: The bluff body has a width of 1m, which makes Re=3,4E5. I believe we are already in a turbulent phase. I followed your recommendations step by step and it has diverged and created great turbulence. I might be in some kind of error but I donīt understand a thing about it because before diverging, the Cd values where very low (errors of 50%). Any other help? Many, many thanks Miguel

 March 2, 2005, 15:27 Re: questions about V2F viscous model #6 Jason Guest   Posts: n/a How many iterations into the solution until it diverges? What solver settings are you using when it diverges? Jason

 March 2, 2005, 19:07 Re: questions about V2F viscous model #7 pieizquierdo (miguel) Guest   Posts: n/a letīs see: -I did what you told me; i.e.Pressure URF=0.5 and Momentum=0,4 I turned off the turbulence equation, run 200 iterations. I turned the equation on and run about 1000 iterations until almost-converged. Then I switched to 2nd order pressure and momentum. It started Diverging about 2600 iterations Now about the solver settings: the settings are: -segregated, implicit, 2D, steady, absolute -About the viscous model: K-e realizable with standard wall functions; c2=1.9; TKE=1; TDR=1,2 Turbulent viscosity=none -About the mesh; skew<0,05 velocity inlet and pressure outlet. The bluff body is something like a bullet and the mesh keeps on for 30 times the bullet lenght behind. I donīt know why but with K-e standard it converged but to a value of Cd around 0,4 whilst the air tunnel value is or ariund Cd=0,7 Any clue? Thanks; Miguel

 March 3, 2005, 10:35 Re: questions about V2F viscous model #8 Jason Guest   Posts: n/a As for the Cd value, two things to consider... Drag on a cylinder doesn't seem to drop until a RNL of about 3-4(10^5) based on the diameter (Hoerner, Fluid-Dynamic Drag). You could be in the transition region, which is notoriously difficult to solve. You could try a laminar model to "bound" your solution. Also, double check your reference values (very common problem). As for the divergence, you'll have to really look at the solution when it diverges to see where the issue is happening. If you save a case and data just after it diverges and send it to me, I'll take a look at it when I get a chance and let you know what I find and what to look for in the future. Hope this helps, and goodluck, Jason

 March 3, 2005, 11:06 Re: questions about V2F viscous model #9 pieizquierdo (miguel) Guest   Posts: n/a thanks Jason I will work on it and I wills end it ASAP Thanks again Miguel

 July 11, 2016, 16:31 #10 New Member   hamide hayati Join Date: Oct 2015 Posts: 28 Rep Power: 4 hi all i want to simulate turbulent flow in a 2D channel (2*40cm) by v2f model. i set it as follow: -i try to use fine mesh near the wall, (y+<=1) -B.C : velocity inlet, v=5 m/s , and define functions for v,k,epsilon and v2.(to be fully developed from beginning of channel) outFlow for end of the channel nosleep fo walls. -second order upwind to solve equations. but unfortunately i can't valid my results!!!!!! for example i can't find u+ vs y+ graph correctly!!! and also v'+ vs y+ and k+ vs y+ near the wall!!!!(1

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