Incorrect lift co-efficients with buoyantBoussinesqPimpleFoam


I have been trying to validate flow over a heated square cylinder using buoyantBoussinesqPimpleFoam. However, the lift coefficient is seen to be positive instead of negative values. Also, the wake is not captured properly. I am using OpenFOAM 5 as the newer versions consider Boussinesq approximation as an equation of state which am afraid is not a proper way.

Please see below the link to my case file and share your suggestions if you have had any similar experiences.


Thank you


OpenFOAM 28-12-20, 12:44 p.m. damu1414

Can you attach the paper you are trying to validate?
Divyesh Variya

29-12-20, 7:15 p.m. divyesh


Hi Divyesh,

Thanks for the response. Please see below the url for literature.

29-12-20, 10:09 p.m. damu1414


Can you cross-check values of velocity, viscosity & Temperature difference?
To use the Boussinesq approximation method, there is a constraint of Temperature difference. In your case, it is 31.5 Which is very large. It seems due to these reasons you are not getting the correct results.

Divyesh Variya

30-12-20, 10:35 a.m. divyesh

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Hi Divyesh, I calculated the parameters as follows. For a particular case, Gr=10^4 and Re=200(as per the literature previously attached), I assumed temperature diff=1. My square cylinder side is of 1 unit. beta=3.33e-03. Hence, V=0.36. nu=1.8e-03. All dimensions as per SI. I ran the case and attached is the Cl-time plot. The value is way too high. Please advise.
30-12-20, 1:07 p.m. damu1414

the case file has velocity value 1 m/s
Temperature difference is 31.5. I think you need to correct and run again.

31-12-20, 10:37 a.m. divyesh

Hi Divyesh,

This output belongs to the new case with parameters as mentioned in my previous comment. 

Gr=10^4, Re=200(as per the literature previously attached)

Temperature diff.(assumed)=1. Square cylinder side is of 1 unit. beta=3.33e-03. V=0.36. nu=1.8e-03. All dimensions as per SI

31-12-20, 11:09 a.m. damu1414

Looks like velocity-viscosity values are not working. Could you try some other combinations by changing temp. diff. or you could get more specific values if you dig some more literature. There are a couple of people who did the same simulations for validation. You could look at their papers.

31-12-20, 12:54 p.m. divyesh

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Hi Divyesh, I tried another case as suggested by you. For Gr=10e4 and Re=200 T(air)=300, T(hot)=301, g=9.81, nu=1.58e-05, beta=3.33e-03. I then calculated characteristic length=0.042 and velocity=0.075. Please see attached the cl-time plot.
31-12-20, 10:14 p.m. damu1414

The characteristic length will be the height of the cylinder and based on the above values grashoff number will give you a temperature difference.
I hope you are using the same domain inlet length. And calculating velocity based on that length with given Reynolds no.

01-01-21, 11:32 a.m. divyesh

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