Learning Forum

[Mia Wan]

Hi I'm currently learning Fluent for my cfd work and I with to simulate an oscillatory aerofoil with sinusoidal behaviours. Currently I wish to use a transient table to vary the boundary conditions to achieve this.

I'd like to ask if time can be defined in this way in transient table? I have tried the case with a time step size of 1s and it worked. But if I reduced the time step size in the transient table into 0.1s, the cfd result did not seem to match. 

Thank you 

[Federico Alzamora Previtali]

Hello, 

yes you can input a varying time step size in Fluent. Regarding your results, I would expect that a time step of 0.1s will capture some transient effects that may not be resolved in a 1s time step - depending on the period of the oscillation for example.

[Mia Wan]

Hi, 

Thank you for your reply! I'd also like to ask if I have a time step size of 0.02s for example, will it be better if I set the calculation time step size also as 0.02s, or a smaller time step size is better? 

[Federico Alzamora Previtali]

I am not sure I understand the difference between the time step you "have" and the time step you "set"? Can you clarify this?

As a general rule, a smaller time step will provide better temporal resolution and accuracy but at the cost of computational time. Hence, you need to balance your choice of time step between those 2 things.