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

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

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

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,