Courant Number Limit in Open Channel flows

anuprdk · September 28, 2014, 12:51

Hi,

I am simulating an open channel flow with explicit conditions. It mentions in the menu (Models -> Multiphase) that CFL number is 0.25. I am running the simulation with a time step of 0.01 second and the running CFL number is in the range 4 to 5 with the convergence criterion being satisfied. I am wondering if I can increase the time step to 0.02 which means a double jump for the CFL number. Also what is the role of the Global Courant number of 0.25 in this context?

Attached herewith is the screenshot of the open channel menu where this CFL is mentioned. cfl.jpg

Thanks

Anup Radhakrishnan

virendra_p · September 29, 2014, 13:16

If you are getting cfl value around 4-5 means your limiting cfl is set to 2 in calculation activities settings....also for multiphase flows it is advised to use cfl of around 0.5....which means that a cell is emptied or filled by a fluid in atleast 2 time steps....thus preventing sudden accelerations of fluid flow and improving convergence, stability and accuracy....

September 28, 2014, 12:51	Courant Number Limit in Open Channel flows	#1
anuprdk New Member anup radhakrishnan Join Date: Jan 2014 Posts: 24 Rep Power: 12	Hi, I am simulating an open channel flow with explicit conditions. It mentions in the menu (Models -> Multiphase) that CFL number is 0.25. I am running the simulation with a time step of 0.01 second and the running CFL number is in the range 4 to 5 with the convergence criterion being satisfied. I am wondering if I can increase the time step to 0.02 which means a double jump for the CFL number. Also what is the role of the Global Courant number of 0.25 in this context? Attached herewith is the screenshot of the open channel menu where this CFL is mentioned. cfl.jpg Thanks Anup Radhakrishnan

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September 29, 2014, 13:16		#2
virendra_p Member Virendrasingh Pawar Join Date: Jun 2013 Posts: 47 Rep Power: 12	If you are getting cfl value around 4-5 means your limiting cfl is set to 2 in calculation activities settings....also for multiphase flows it is advised to use cfl of around 0.5....which means that a cell is emptied or filled by a fluid in atleast 2 time steps....thus preventing sudden accelerations of fluid flow and improving convergence, stability and accuracy....