# validation

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 January 11, 2009, 06:14 validation #1 fathan Guest   Posts: n/a Sponsored Links hai, anybody know how to make some prepin validation for drag airfoil. i have create it but the result didn't match @ reference drag coef is 0.6 but my result is 0.998. i use it for chambered airfoil.

 January 14, 2009, 05:04 Re: validation #2 Stefano Guest   Posts: n/a hello fathan, what is the minimum cell size, respect the chord lenght? And which momentum approximation ("iorder" variable)do you use for this kind of simulations?

 January 14, 2009, 12:32 Re: validation #3 Fathan Guest   Posts: n/a Hello stefano, i use cell size is 8 mm for chord lenght 0.4 m. And iorder is 1 " first order".

 January 14, 2009, 13:33 Re: validation #4 Fathan Guest   Posts: n/a Hello stefano, my chord lenght is 0.4 meter and cell size is 8mm, i use iorder=1.

 January 15, 2009, 03:47 Re: validation #5 Stefano Guest   Posts: n/a hello Fathan, you can try to make a restart from this your simulation when it is finished, and in the restart simulation you can try to switch to iorder=3 and a minimum cell size of 4mm. But I forgot to ask you the fluid speed and how many mesh blocks you are using... so I'm worried that if the fluid speed is too high or if you are not using multi-blocks you may have a long simulation time.

 January 15, 2009, 10:05 Re: validation #6 Fathan Guest   Posts: n/a For vel i use 1 m/s (thats low speed) and i do for 1 mesh..

 January 15, 2009, 10:33 Re: validation #7 Stefano Guest   Posts: n/a the simulation than should be quite fast. However if you want to speed up your simulation you can think to use 2 or 3 mesh blocks, nested, with the inner one with the cell of 1% of the length, and the outer ones with a bigger cell.

 January 16, 2009, 02:42 Re: validation #8 Fathan Guest   Posts: n/a Thnks stefano, the mesh now good enough, but if i use idrg not equal 2 the result=1, im use idrg=2. Why its diffrnt, i dont understood? Have i to use obstcle porosity? What are variable i have to use?

 January 16, 2009, 03:44 Re: validation #9 Stefano Guest   Posts: n/a Fathan, why are you using the idrg variable? IDRG is made in case you want to model any porous obstacle, is your geometry porous?

 January 16, 2009, 09:08 Re: validation #10 fathan Guest   Posts: n/a my airfoil doesn't have porousity. i use it bcoz at output a dont see drag coef. and i try to using IDRG and the output appear. how to appear the drag coeff?? i'm confused

 January 16, 2009, 09:15 Re: validation #11 Stefano Guest   Posts: n/a the drag coefficient that you are looking at is not the drag coefficient of the airfoil, but simply the drag due to the porous obstacle. So not the right output. You don't have a direct output of the drag coefficient in FLOW-3D. In FLOW-3D outputs you have the force that acts on the airfoil, then you have manually to adimensionalize to have the Cd. To have the forces that act on your geometry, the fastest way is to define your airfoil as a GMO with "prescribed motion". When the simulation is done, in "Analyze" -> "Probe" -> "general history" you have the forces that act on the GMO.

 January 16, 2009, 09:29 Re: validation #12 fathan Guest   Posts: n/a there is a lot of output, where i should to use? i use f3d V8.2 and thats have no analize button but in result ->probe.

 January 16, 2009, 09:43 Re: validation #13 Stefano Guest   Posts: n/a with 8.2 you don't have the General Moving Obstacle model. You should use a Force Window then (you can find it in the Manual) or think to upgrade. Newer versions will give you a lot of new features and more accurate simulations!

 January 16, 2009, 09:58 Re: validation #14 fathan Guest   Posts: n/a I see, i use f3d for my graduation so, i need this information.. thank you for attention and your regard.. i will try to use force window.. thats right, it should be upgrade.. i think it will be upgrade in 2009-2010 Btw, where are you from??

 January 16, 2009, 11:08 Re: validation #15 Stefano Guest   Posts: n/a Than you can be succesfully by using the "Force Window"! Use it and the hints of this discussion and you'll have good results also with your 8.2! I'm from Italy.

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