# Initial conditions in CFX 5.5

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 December 18, 2001, 03:22 Initial conditions in CFX 5.5 #1 Astrid Guest   Posts: n/a Hi All, I would like to study the mixing of a hot and a cold fluid. Initially there are two separate containers, one cold, one hot. At t=0 the get connected. See the figure below. ____ ____ | | | | | | | | | |___| | |hot ___ cold| | | | | | | | | |____| |____| My question is how to set the intial temperature distribution in CFX 5.5. Any suggestion? Thanx, Astrid

 December 18, 2001, 15:31 Re: Initial conditions in CFX 5.5 #2 Robin Steed Guest   Posts: n/a Hi Astrid, A step function will allow you to initialize your fluid temperature with a sharp boundary between hot and cold fluids. The syntax is pretty simple, just make sure the value within the step function is dimensionless. A step function evaluates to zero when the value is negative, one when the value is positive, and 1/2 when the value is zero. Here's an example: initial_T = 350 [K] - step((x - 2 [m])/1 [m])* 50 This would create a step change from 350 Kelvin down to 300 Kelvin, at x = 2 meters. The divide by 1 [m] makes the term within the step function dimensionless. Regards, Robin

 December 18, 2001, 17:37 Re: Initial conditions in CFX 5.5 #3 Astrid Guest   Posts: n/a Hi Robin, This was one of the routes I had in mind. I am still in a kind of 'CFX4-mind': giving different blocks a different initial temperature. I was trying to define two domains with two different temperatures but had no success. Can you confirm this a route to nowhere? Thanx, Astrid

 December 19, 2001, 00:24 Re: Initial conditions in CFX 5.5 #4 Robin Steed Guest   Posts: n/a Hi Astrid, If you only have one subdomain, there is also a function, subdomain, which has a value of 1 in a subdomain and zero elsewhere. Other than that, CEL will have to do. Robin

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