I am a beginer to cfd and looking for information on methods used for gradient calculation in CFD. Please guide me on the topic.

Thanking You Apurva Shukla

Because diffusion and convection fluxes are inherently different phenomena, they are normally modelled totally differently in CFD.

Diffusion terms can be thought of as equal spreading of a flow property in all direction and is normally modelled with central diff. discretization scheme

However convection is depended mainly on flow direction, it is normally model with upwind, power law, 2nd order etc. discretization schemes

You say you are a beginner, therefore a good book to Start off with is " An introduction to computational fluid Dynamics

The Finite Volume Method" By HK Versteeg and W Malalasekera