define Reynolds number in CFX

Tommy Chen · August 14, 2016, 03:51

Hi I got a problem while using ANSYS CFX , the case I'm going to run is an aircraft cruising at 10 km high with mach=0.75. Usually when I was doing with the CFD code like SU2 or the inhouse code of our lab, I could easily set the reynolds number to be a certain value. Reynolds number is one of the three similarity parameters, with the other two as mach number and the scaled shape.

However, in CFX, is there a way for me to directly set the Reynolds number that could match the case ? If not, I guess I have to change the gas property to indirectly tune the Renolds number, then how could I do it ?

ghorrocks · August 14, 2016, 08:41

CFX is a primitive variables solver. So it solves in pressure, velocity, temperature.

If you want to specify something as a Reynolds number you are going to have to define the velocity, density, length scale and viscosity it involves directly. Then to change the Re you change the parameters to get the new Re. In your case as this is probably an aircraft flying faster and slower - then I would just change the velocity.

August 14, 2016, 03:51	define Reynolds number in CFX	#1
Tommy Chen Member Tommy Chen Join Date: Mar 2011 Location: University of Michigan Posts: 96 Rep Power: 15	Hi I got a problem while using ANSYS CFX , the case I'm going to run is an aircraft cruising at 10 km high with mach=0.75. Usually when I was doing with the CFD code like SU2 or the inhouse code of our lab, I could easily set the reynolds number to be a certain value. Reynolds number is one of the three similarity parameters, with the other two as mach number and the scaled shape. However, in CFX, is there a way for me to directly set the Reynolds number that could match the case ? If not, I guess I have to change the gas property to indirectly tune the Renolds number, then how could I do it ?

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August 14, 2016, 08:41		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	CFX is a primitive variables solver. So it solves in pressure, velocity, temperature. If you want to specify something as a Reynolds number you are going to have to define the velocity, density, length scale and viscosity it involves directly. Then to change the Re you change the parameters to get the new Re. In your case as this is probably an aircraft flying faster and slower - then I would just change the velocity.