courant number

rasool motamedi · May 19, 2013, 07:52

Hi
I am simulating a rotating blade and it is transient.
min mesh size is 5 micro meter
max mesh size is 20 micro meter
my blade rotate 600 rpm
inlet velocity is 13333 micro meter per secound
how can define below things:

1-min and max courant number
2-best time step

is max courant number=0.2 good?
and dt=0.00001 good?
thanks regards

ghorrocks · May 19, 2013, 08:24

Courant number is not relevant for CFX as it is an implicit solver. I do not recommend using it to set time step size. For most transient simulations in CFX the best way to control the time step size is using adaptive time steps, homing in on 3-5 coeff loops per iteration.

rasool motamedi · May 19, 2013, 08:37

hi
so Why in solver control when I active secound order backward I can define min and max courant number?

ghorrocks · May 19, 2013, 08:49

Just because an option is available does not mean it is a good idea to use it.

JuPa · May 19, 2013, 12:52

This is a good read:

http://www.flow3d.com/cfd-101/cfd-10...t-schemes.html

May 19, 2013, 07:52	courant number	#1
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	Hi I am simulating a rotating blade and it is transient. min mesh size is 5 micro meter max mesh size is 20 micro meter my blade rotate 600 rpm inlet velocity is 13333 micro meter per secound how can define below things: 1-min and max courant number 2-best time step is max courant number=0.2 good? and dt=0.00001 good? thanks regards

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May 19, 2013, 08:24		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Courant number is not relevant for CFX as it is an implicit solver. I do not recommend using it to set time step size. For most transient simulations in CFX the best way to control the time step size is using adaptive time steps, homing in on 3-5 coeff loops per iteration.

May 19, 2013, 08:37		#3
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	hi so Why in solver control when I active secound order backward I can define min and max courant number?

May 19, 2013, 08:49		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Just because an option is available does not mean it is a good idea to use it.

May 19, 2013, 12:52		#5
JuPa Senior Member Mr CFD Join Date: Jun 2012 Location: Britain Posts: 361 Rep Power: 15	This is a good read: http://www.flow3d.com/cfd-101/cfd-10...t-schemes.html