How to get Pressure field from velocity field
Once I got a flow field which is divergence free, how can I calculate the coresponding pressure field then I can get the pressure drop.
Thx 
Re: How to get Pressure field from velocity field
Given a divergencefree flow field, the "pressure Poisson" equation can be used to calculate the pressure from the velocity.

Re: How to get Pressure field from velocity field
Could apply Bernoulli's Theorem whereby:
Cp = (P  Pref) / (rho.Vref^2 / 2) Cp = 1  q^2 / Vref^2 where Cp = Pressure Coefficient, P = Static Pressure at x, Pref = Reference Static Pressure, rho = density, Vref = Reference Velocity Magnitude, q = Velocity Magnitude at x 
Re: How to get Pressure field from velocity field
This implies you know Cp. It also applies to particular physics (check basic fluid dynamics books). The pressure Poisson equation suggested By Jonas is the answer. Apply the divergence operator to the NavierStokes equation and use "continuity" for incompressible flow to get the source term for the Poisson equation
adrin 
Re: How to get Pressure field from velocity field
Of course you are both right on the Poisson equation being the most general solution for an incompressible flow.
However, for an invisid flow Bernoulli's is valid without knowing Cp  rearranging the original formula to eliminate Cp  gives static pressure directly as: P = Pref + (rho / 2).(Vref^2  q^2) Given the original poster only specified they had a divergence free velocity field I presumed they may have obtained it from an inviscid methodology such as a panel method. 
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