it's about the algorithm for solving equations. The Navier Stockes and continuity equations are solved by iteration. The SIMPLE algorithm, for example, gives a first estimated value, which subsequently corrects it by a new, more precise value in order to satisfy the continuity.

To stabilize the calculation, we update the old variables by a certain rate like that:

Φ = Φold + α(Φnew − Φold)

If α = 1, Φ = Φnew : maximum renewal

If α = 0, Φ = Φold : no evolution of the solution

Leave by default and see if your calculation converges.

If it does not converge, it is advisable to gradually reduce this relaxation factor and observe the solutions. It works like a catalyst but be careful to the physical coherence of your results.

In fact, having a very low residue does not mean a physically consistent solution.

P.S: I can't see correctly your screenshot, it's a bad quality

Thank you very much for answer !

and about your 2nd question, i cant read