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-   -   reference value (http://www.cfd-online.com/Forums/fluent/27376-reference-value.html)

Xia Jian November 22, 1999 12:41

reference value
 
Dear friends,

I am a new user of Fluent.I find it difficult for me to get accurate Cl,Cd and Cm even in very simple cases: 1.2-D Euler equations Naca-0012 airfoil Mach infinite = 0.8 Alpha = 1.25 degree 2.3-D Euler equations M6 wing Mach infinite = 0.84 Alpha = 3.06 The Cl,Cd and Cm obtained using Fluent can be much larger or less than the values pointed by many reference.I think I choose the right refernce value. Could you tell me why? Thanks in advance.

Xia Jian

chris November 23, 1999 02:14

Re: reference value
 
First check the reference values for velocity, area... and look then at the exact fluent-definition of cl, cd and cm in the manual. chris

Althea November 23, 1999 11:35

Drag Predictions
 
Hello Xia,

I have also had difficulties predicting drag using Fluent(5). I am ultimately interested in engine intakes, but to start off ran simulations of simple 2 and 3D shapes for which I knew the drag coefficient. I found I could get the correct values for drag coefficient and drag force, but only after a lot of y+ adaption, even when I had predicted the size of the first cell as Fluent recommended.

My concern is that when I am modelling something I don't have the answers for, how will I know when I reach the correct result?

I would appreciate any suggestions people out there have since I know I will have more work coming up in this field.

All the best and good luck with your simulations. I would be very interested to hear how you get on.

Althea

Ali Oge November 23, 1999 13:04

Re: Drag Predictions
 
Hi,

Drag coefficient is affacted by discretization order (depending your mesh)and turbulance models. My suggestion is that using high order discretization ( for example 2.order or QUICK for momentum)and powerfull turbulance models like Realizable k-e.

Ali,


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