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-   -   Reference values resetting? (http://www.cfd-online.com/Forums/fluent/110554-reference-values-resetting.html)

cad2blender December 13, 2012 21:25

Reference values resetting?
 
I am modelling a car with one front wing and one rear wing inside a domain. I would like to know how to setup the reference values correctly. So far I have used the default values but I now realize that this is not correct.By selecting "Front Wing" under "compute from" I am able to select the planform area which is fine. The problem is when I try to input the rear wing planform area. When I select "Rear Wing" the value that I inputed for the front wing gets overwritten by the value for the "Rear Wing" Is this not the correct way of inputing reference values?

EDIT: Perhaps I only need to input one reference value for one wing and the values that I need (lift,drag, CL, CD) should be correct?

LuckyTran December 13, 2012 23:54

The resetting is normal behavior.

Quote:

Originally Posted by cad2blender (Post 397455)
EDIT: Perhaps I only need to input one reference value for one wing and the values that I need (lift,drag, CL, CD) should be correct?

In general you might need different reference values. Most people define the coefficients based on the same reference values (for convenience) in order to deal with the issue you are having.

You can only specify one set of reference values at a time. Fluent uses these reference values to compute certain quantities (lift, drag, etc.) globally. If you want to compute these quantities for two sections that might possibly have difference reference values, such as cross sectional area, then you need to change the reference values accordingly before you compute the quantities for that section. i.e. set the reference values using the front wing and then calculate lift on the front wing. Then change the reference values for the rear wing and then calculate lift on the rear wing.

The reference values should be user specified (by you). These should be the correct reference values in accordance with the definitions of lift,drag, CL and CD. It is better to input them explicitly rather than using compute from. But if compute from is working for you then by all means use it.


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