# Change density; reynolds number

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 April 4, 2012, 10:31 Change density; reynolds number #1 New Member   Thierry Chavagnan Join Date: Apr 2012 Posts: 6 Rep Power: 6 Hi everyone!!!! Im doing my dissertation on a modified Clark Y wing. I only just started usiing ANSYS and I would like to know how can I change the density of the air or reynolds number. I would like to simulate an aircraft flying at 5000m. Thank you for your consideration

 April 4, 2012, 17:55 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 CFX is a dimensional solver. This means you have to give it input values in a consistent set of units - usually SI, so metres, seconds, Kelvin, kg. You cannot give it inputs in non-dimensional numbers like Reynolds number. So you simply convert your Reynolds number to a set of dimensional values, that is a density, velocity and viscosity. If you are modelling a airfoil in air then use air properties and work out the velocity from there. Changing the density is trivial - have a look at the tutorials for how to set material properties.

 April 5, 2012, 04:39 #3 New Member   Thierry Chavagnan Join Date: Apr 2012 Posts: 6 Rep Power: 6 Thank you so much for replying. I managed to change the density but Im not sure whether to use ideal gas or real gas. I want to simulate the wing flying at an altitude of 3000m. I was thinking that if I use ideal gas, this might use less computingting power and less time. Will there any big difference in the results between using ideal or real gas??? I read that real gas should be use on for supersonic speed but my experiment is being done at low subsonic. What are your thought please??? Thank you

 April 5, 2012, 16:17 #4 New Member   Mohammed Join Date: Apr 2012 Posts: 2 Rep Power: 0 No point in treating it as a real gas.

 April 5, 2012, 17:04 #5 New Member   Thierry Chavagnan Join Date: Apr 2012 Posts: 6 Rep Power: 6 Cheers guys...!!! Thank you so much for your help. I have one last question, does anyone know how I can get lift & drag coefficient produced by my wing from the results obtained in CFX-post???? The only results that I have got were: velocity, pressure, eddy viscosity and some others.... Bearing in mind that my simulation was in 3D Thanks again guys, your help is much appreciated and your name is definitely going to be in my acknowledgement with your permission of course.

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