  We present an explicit finite difference method to simulate the non-ideal
multi-phase fluid flow. The local density and the momentum transport are
modeled by the Navier-Stokes (N-S) equations and the pressure is computed by
the Van der Waals equation of the state (EOS). The static droplet and the
dynamics of liquid-vapor separation simulations are performed as validations of
this numerical scheme. In particular, to maintain the thermodynamic
consistency, we propose a general wetting energy boundary condition at the
contact line between fluids and the solid boundary. We conduct a series of
comparisons between the current boundary condition and the constant contact
angle boundary condition as well as the stress-balanced boundary condition.
This boundary condition alleviates the instability induced by the constant
contact angle boundary condition at $\theta \approx0 $ and $\theta \approx
\pi$. Using this boundary condition, the equilibrium contact angle is correctly
recovered and the contact line dynamics are consistent with the simulation by
applying a stress-balanced boundary condition. Nevertheless, unlike the
stress-balanced boundary condition for which we need to further introduce the
interface thickness parameter, the current boundary condition implicitly
incorporates the interface thickness information into the wetting energy.
