Convergence in transient simulation
 

Hello,

I am modelling transient natural convection in FLUENT.
The geometry is 2D axis
I activated the gravity

The time step is 0.1s, the max iteration/time step is 100. I decreased the time step to 0.001s but I got the same results.
The residuals are not converged between two time step so this makes the final resultat( e.g the temperature) wrong. I have attached a picture showing the residuals obtained.

Can you please help me to solve this problem?

The text user interface clearly states that your "solution is converged", which means that the residuals are lower than the limits you set. What exactly is the problem?

Actually my tutor told me that when we model a transient case, the residual should converge between each time step as shown in the picture attached. In my case, it doesn't converge between each time step

That is a different kind of convergence ;)
To have the residuals level out within each time step switch off convergence criteria in the monitors section. Then each time step will be calculated with the 100 iterations you entered.