[Aimen_Sattar]

Hi,

I am trying to model transient response of a porous model to a step reduction in the temperature of one of it's surfaces. I have set the physics model to 'Implicit Unsteady' and have noticed that where I used to input the constant temperature of the surface (in the steady model), there are a number of options including fields as functions of r, t, x,y,z etc.

I would greatly appreciate any help

Thanks

Aimen

[Jonny6001]

Since you have turned the unsteady model on, you now have the option of specifying transient boundary conditions.
If you want the temperature of a wall to change with time, you need to import a table in .csv format which has Time in the first column and Temperature in the second. Then tell Star that you want to use this imported table Table(Time) as the boundary definition for temperature field function.
You can specify more complex transient temperature profiles but if you want the entire boundary to be the same temperature use the simple option.

[abdul099]

When you just want to change the temperature once or with let say two or three steps, you might write a field function.

Simple example:
$Time<=10.0?500$Time<=20.0?300:200)
This field function changes the value from 500 to 300 after 10 seconds and to 200 after 20 seconds.

For more steps, you should use a table like Jonny mentioned before.