Try to understand the practice of under-relaxation
 

Dear all member,

Greetings guys, I've been reading "An Introduction to Computational Fluid Dynamics: The Finite Volume Method" to get some basic concept of how SIMPLE algorithm works.

I read about the section of under-relaxing the linked coefficients, velocity field from previous iteration. It also says *the under-relaxation is used from the start of the calculation*.

My questions are,
1. Is the under-relaxation applied at the 1st iteration (like applying to coefficient Ap)?
2. Is it necessary that the sum of pressure relaxation factor and velocity relaxation factor equals to 1?

Thanks,
Rick

1. Yes to my knowledge the under-relaxation is built into the algorithm (you are probably reading SIMPLE algorithm) and applied from the 1st iteration.
2. No it is not necessary to keep it as 1 (It is a good common practice). You can run the simulation even without the under-relaxation factors hoping to get a solution.

Thank you very much. I am going to try coding it.