CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Main CFD Forum (http://www.cfd-online.com/Forums/main/)
-   -   CFL number and time accuracy for LES (http://www.cfd-online.com/Forums/main/4947-cfl-number-time-accuracy-les.html)

Li Yang July 19, 2002 05:05

CFL number and time accuracy for LES
 
Dear all,

I am now doing LES using SIMPLE based solver. I use the Crank-Nicolson scheme in time and the central difference scheme in space. I would like to use the fully implicit scheme in time as well.

My questions are: (1) Which scheme would allow me to use a larger CFL number and how large a CFL number you normally used? (2) How do I know my solution is time accurate ?

Thank you very much in advance.

Li


baal July 28, 2002 02:47

Re: CFL number and time accuracy for LES
 
hello,i finished the code of les program with fortran,and i use implicit scheme,but when cfl is 1.22,the convergent rate is very small,could you help me?thanks

adarsh August 1, 2002 06:11

Re: CFL number and time accuracy for LES
 
for implicit schemes any CFL can lead you to convergence .Cfl nos up to 20 has been used.but the accuracy of solution goes down as CFL no. increases.For time accuracy u can also use jameson's method of false time stepping.

but if the samllest time scale of the flow as given by kolmogorov scales is less , the it becomes a restricting factor and convergence can be affected.

hope this helps Adarsh


All times are GMT -4. The time now is 16:04.