all the text books and references seem to suggest that the drag coeffecient for a circular cylinder for reynolds number 10000, 100000 are about 1.2 approximtely. but when i am using flent i get values of about 0.1- 0.2 (max). i dont seem to understand whats going wrong. i have consulted some people in this area but they tell me that i am right and they cant figure why fluent is giving me such weird values. please help me out here as i am in deep trouble and have a deadline to submit. thanking you. allan

Allan you might find it helpful to look at the reference values you give in the panel since the coefficients depend on them as well.

Also try different turbulence models......

Hope it resolves your problem.

Cheers....

Yes, check the reference values that are being used to calculate lift and drag coefficients. There are default values like L=1m, etc. You have to change these to the appropriate values for your system.

I guess the problem is still there, One can change and play around with the parameters to get the results to ones liking. There has to be some standard methodology so that whenever one intend to carry out analysis on shapes and configurations with unknown results. Can anyone throw some light on it?

I contacted the Fluent engineer, who told me to increase the depth in the reference values to 10.

This increased the CD to the desired value (around 1). However, when I increase the flow velocity from the original value, the CD jumped to over 9000 (it should be around 0.3).

You can easily get the CD to the value you want by altering the depth value, but this isn't right.

Does anyone know if there is a standard method to find the correct depth value?