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-   -   Define area and depth for drag coefficient calculation for flow over of cylinders (http://www.cfd-online.com/Forums/fluent/103582-define-area-depth-drag-coefficient-calculation-flow-over-cylinders.html)

 engr June 20, 2012 22:59

Define area and depth for drag coefficient calculation for flow over of cylinders

I want to calculate coefficeint of drag (Cd) using fluent; for the flow over cylinder:
Dia of cylinder= 0.05 m
Re=500

what Reference values should I used in fluent to find the Cd as defaults values are 1 for area,depth and length.
Area=?
density=1.225
Depth=?
Length=?
Velocity=0.14607
Viscosity=1.7894e-05

When I calculated Cd using Report>Forces> cylinder wall. the results are not matched with available experimental results.

 chris85 June 21, 2012 04:42

Quote:
 Originally Posted by engr (Post 367566) I want to calculate coefficeint of drag (Cd) using fluent; for the flow over cylinder: Dia of cylinder= 0.05 m Re=500 what Reference values should I used in fluent to find the Cd as defaults values are 1 for area,depth and length. Area=? density=1.225 Depth=? Length=? Velocity=0.14607 Viscosity=1.7894e-05 When I calculated Cd using Report>Forces> cylinder wall. the results are not matched with available experimental results.
As far as I know area should be the frontal cross sectional area, depth would be the lenght of the cylinder if in cross flow, lenght is the characteristic length of the cylinder.

The force you get from fluent is not Cd, it will give you Fd and you need to change this to Cd. I think it is:

Cd=(2*Fd)/[density*(V^2)*A]

 engr June 21, 2012 04:51

Thanks chris

I read somewhere that total coefficient we got from Report>forces>, is a drag coefficient. please correct me if I am wrong

In Forces report we can get Pressure, viscous and total coefficient.

 sajid December 13, 2012 16:27

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=?

 engr December 17, 2012 21:34

In Ansys Fluent Reference Length= Diameter of Circle, and as you mention its 2D so your depth=1, and Area means frontal area= reference Length*Depth
(whether have to use area of 2 or 4 circles ???) I am not sure about this as i am using only one cylinder,i think you should use 2 circles diameter as your length and same as frontal area as your depth equals 1.

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