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-   -   calculating drag and lift in fluent (http://www.cfd-online.com/Forums/fluent/81426-calculating-drag-lift-fluent.html)

morteza08 October 26, 2010 17:09

calculating drag and lift in fluent
 
hi i have modelled so many airfoils in fluent ...but the drag and lift coefficients are not exactly those in experimental results.
is there any other way to calculate drag and lift manually in fluent???

akhokhay October 28, 2010 09:19

Quote:

Originally Posted by morteza08 (Post 280860)
hi i have modelled so many airfoils in fluent ...but the drag and lift coefficients are not exactly those in experimental results.
is there any other way to calculate drag and lift manually in fluent???

You can use report function and calculate life force, then also calculate area (u can use fluent OR u have it from design map) then u got density of air (hope that's constant! not in compressible flow) then do it from:
Lift=0.5(density)(velocity^2)*(area)

Note:
Velocity is free stream velocity( Am I right)

and also make sure u have correct values in reference values tab in fluent before taking report


IF u still got error try to:
make ur mesh finer


By the way consider numerical errors too! I think (not sure again) up to 10% difference is fine! with normal meshes ! but if u use parallel computers and higher number of mesh it would be lower

Also I am happy if someone correct me if I am wrong


Movafagh bashi

Regards,
Amir

momahadi30 March 9, 2012 13:46

Reference area is wing plan-form area, and the reference length must be considered in calculating pitching, rolling and yawing moment, for cm (pitching) the reference length is Mean Aerodynamic Chord, but for rolling and yawing the reference length is wing Span.
the wing plan-form area is projected area on the top view of the wing

momahadi30 March 9, 2012 13:50

Quote:

Originally Posted by morteza08 (Post 280860)
hi i have modelled so many airfoils in fluent ...but the drag and lift coefficients are not exactly those in experimental results.
is there any other way to calculate drag and lift manually in fluent???

it is very hard to predict aerodynamics forces and moments in CFD, because it is depending on many things like
-Meshing Construction
-Y+
-Boundary layer consideration
-Turbulent modelling
-Flow solver Residuals and covergence round-off errors
-how user is good in solving problems and experience

sajid December 13, 2012 16:34

area problem
 
1 Attachment(s)
i want to calculate area of circles which would be used in ansys fluent ....
it is 2d heat exchanger and i have problem how to calculate area of circle in front of flow or which area i have to put in reference value ..
i have confusion whether i have to use area of 2 or 4 circles ???
kindly tell me how to calculate this area or which area i have to put in reference value ??? i have attached the jpeg. file of structure to further explain it ?
waiting for answer...i will be very thankful to you.
what Reference values should I used in fluent to find the area as defaults values are 1 for area,depth and length.
Area=?
Depth=?


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