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May 29, 2014, 08:27 
Inclusion of density while calculating power

#1 
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Hello,
I am having a little confusion right now. In the source codes of incompressible flow solvers of OpenFOAM I have seen that, pressure quantity is divided with density rho beforehand in order to get dynamic pressure. Now my question is that, as rho is already used to get dynamic pressure do I need to use density while calculating power coefficient of turbo machinaries? I mean by the definition of Cp = Power_Produced/ (0.5* projected area * density * velocity^3). Now do I need to add density in this calculation?
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May 29, 2014, 11:49 

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Chris Sideroff
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May 29, 2014, 11:56 

#3 
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Thanks for your reply.
But I think I have solved the problem. It is little bit puzzling. I would try to give a short explanation. cfd.jpg The attached is the force file from propeller tutorial. As you may see the rhoinfo has been kept 1. But if you give rhoinfo as 1000 or any other quantity the output would change. However the best practice is to keep rhoinfo 1. Thank you all.
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May 29, 2014, 12:57 

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June 9, 2014, 07:57 

#5 
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I am sorry to write again.
Assume I am calculating which needs density say power coefficeint. If the input of rhoinf is 1. Then the calculation would be simply like: Cp= Power produced/(0.5*Area*v^3). But if the rhoinf is 1.25, then the Cp would be like: Cp = Power produced/(0.5*1.25*Area*v^3). Same thing could go for pressure coefficient too. Are my assumptions correct?
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June 10, 2014, 16:18 

#6 
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Chris Sideroff
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Yes, that's correct


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