I have completed a analysis using air as a fluid. Now I want to do same analysis using nytrogen as a fluid. The only change is fluid, nothing else. Can I have some co-relation to predict the results, or I need to do the whole analysis again?

if you are using an incompresible fluid, you don't need to do de analysis again; the properties of the air and nytrogen are similar and you have the Reynolds number to compare both cases.

Hugo