How solver works?i.e. after solver starts how it calculates values of pressure and velocity?does it initially take all values zero?This is as i have observed when solver is running?

The initial values are set via the PIL variables FIINIT(PHI) where PHI is the dependent variable. The default values are 1.E-10. The solver can operate slabwise (at each iz slab in the z direction solve for each phi in turn) or whole-field (for each phi solve for aa values simultaneously over the whole field). Usually, the pressure-correction equation (continuity) and scalar variables are solved whole-field. A SIMPLE based algorithm is used, iei segregated solution of the pressure and velocities.