Sir, thanks for answering my queries,
I did decompositions in many ways, I am refraining myself from using mesh adaptation, as I have to do parametric analysis of the geometry, getting good solution using default mesh is necessary. (This is my understanding of mesh adaptation not sure I am right or not, according to me it is generally used to improve the cells with some conditions for e.g. gradient of a field variable or volume change smoothening, but the problem is I have to do mesh adaptation every time for different parametric cases)
I am getting okayish kind of solution (Mass Imbalance is less than 1% of entire domain) using explicit method, but with implicit solver the residuals blows off.
Sir could you please look into this post, as here I have attached the various decompositions types, I have tried.