[Abhishek.iitb]

I am working on a 3D transient CFD model which deals with the Material flow of metals (Friction stir welding model). It is a coupled fluid flow(material) and heat transfer model using the SIMPLE algorithm to solve fluid flow.
I am facing some problems with the time step. In the Friction stir welding, the order of the Viscosity of metals remains high (~10^6 in SI unit), which makes the time step very small due to restrictions of 'dt' in SIMPLE. It reaches to the order of (dt<1e-12 sec) which makes it difficult for such a small time step. Increasing the time-step generates numerical stability errors. I have tried pressure under-relaxation in correction loop in SIMPLE but it has a certain limits to which we can increase the dt.
So is there any other alternative I can use to avoid such a small time step or to remove time dependence of correction loop?