URANS in ANSYS CFX

brissyben · October 3, 2009, 07:08

Hi ,

I have completed some RANS simulations of a submarine model at a relativley high Re number. I am now trying to start a URANS simulation,

How do you go about starting an URANS simulation in ANSYS CFX? How does this vary from a transient run in ANSYS CFX or is URANS a transient run with RANS model applied?

I have tried to look in the ANSYS help document with out much luck, any help would be great,

Thanks,

Ben

ghorrocks · October 5, 2009, 19:48

URANS is, in its simplest form, simply using the RANS equations in a transient simulation. As the Reynolds averaged NS equations assume steady state you have to be careful that there is a separation between turbulent timescales and flow timescales and that you simulation is correctly resolving this timescale difference.

URANS is the simplest approach for unsteady turbulence simulations. If its underlying approach is not applicable then you need to move to more advanced techniques like DES, SAS or LES. Shedding of vorticies behind a bluff body is an example which is tricky with URANS and lends itself more to the DES/SAS/LES approaches.

brissyben · October 5, 2009, 20:45

Thanks for your help Glen,

Does ANSYS CFX have the ability to do DES or SAS simulations?

ghorrocks · October 6, 2009, 18:35

Yes, CFX can do DES, SAS and LES.

October 3, 2009, 07:08	URANS in ANSYS CFX	#1
brissyben New Member Ben Join Date: Jun 2009 Location: Tasmania Posts: 16 Rep Power: 17	Hi , I have completed some RANS simulations of a submarine model at a relativley high Re number. I am now trying to start a URANS simulation, How do you go about starting an URANS simulation in ANSYS CFX? How does this vary from a transient run in ANSYS CFX or is URANS a transient run with RANS model applied? I have tried to look in the ANSYS help document with out much luck, any help would be great, Thanks, Ben

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October 5, 2009, 19:48		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	URANS is, in its simplest form, simply using the RANS equations in a transient simulation. As the Reynolds averaged NS equations assume steady state you have to be careful that there is a separation between turbulent timescales and flow timescales and that you simulation is correctly resolving this timescale difference. URANS is the simplest approach for unsteady turbulence simulations. If its underlying approach is not applicable then you need to move to more advanced techniques like DES, SAS or LES. Shedding of vorticies behind a bluff body is an example which is tricky with URANS and lends itself more to the DES/SAS/LES approaches.

October 5, 2009, 20:45		#3
brissyben New Member Ben Join Date: Jun 2009 Location: Tasmania Posts: 16 Rep Power: 17	Thanks for your help Glen, Does ANSYS CFX have the ability to do DES or SAS simulations?

October 6, 2009, 18:35		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Yes, CFX can do DES, SAS and LES.