Hi @Get_Barried and @smittag, relaxation factors are used when there are more outer iterations than 1, the PIMPLE algorithm, for example, can be set to iterate at each time step with many outer correctors much like the steady state solver SIMPLE, and the relaxation factors are used to gain stability when many iterations are required to get to a converged state. In contrast when there is only a single iteration from one-time step to another (like PISO) then relaxation is 1, and the solution must be found in that iteration, if you do not then the residuals start to raise and you may incur divergence. If you download a case you can see that the outer correctors are not specified, and therefore default to 1. If Courant number is low this shouldn’t bare any issues.
If you need more info however, you might be best reading up on the different algorithms and interDyMFoam which is used.
Hope this helps,
Darren