Characteristic boundary conditions that are capable of handling
general fluid mixtures flow at all flow speeds are developed.
The formulation is based on fundamental thermodynamics theories
incorporated into an efficient preconditioning scheme in a
unified manner. Local one-dimensional inviscid (LODI) relations
compatible to the preconditioning system are proposed to obtain
information carried by incoming characteristic waves at
boundaries accurately. The approach has been validated against
a variety of sample problems at a broad range of fluid states
and flow speeds. Both acoustic waves and hydrodynamic flow
features can pass through the boundaries of computational
domain transparently without any unphysical reflection or
spurious distortion. The approach can be reliably applied to
fluid flows at extensive thermodynamic states and flow speeds
in numerical simulations. Moreover, the use of the boundary
condition shows to improve the computational efficiency.