A characteristic wave analysis previously developed to specify boundary conditions for chemically reacting flows with realistic thermodynamic properties is derived with an alternative set of primitive variables. In a multicomponent reacting flow, it is sufficient to consider the time-integratio of all species' mass fractions, excluding one. This results in a primitive vaiables vector that contains one element less. The impact of this choice on the resulting characteristic equations and treatment of numerical boundary conditions are presented. The improved accuracy in the treatment of boundary conditions is assessed via three test problems including non-reacting and reacting situations. The method presented is found to provide accurate results as it allows acoustic waves, pressure waves and vortices to propagate through the domain without discernible reflection. Furthermore, the method eliminates the drift of the mean pressure that tends to occur over long integration times when the boundary is treated inaccurately.
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