ENTROPY PRODUCTION IN NONSTEADY GENERAL COORDINATES

The second law of thermodynamics is generally not utilized in CFD algorithms, since the law is not essential for obtaining a flowfield solution. However, there are circumstances where the relevance of the second law should not be overlooked. These occur in flows where the entropy production by natural (i. e. , irreversible) processes is large, e. g. , a chemically reacting boundary layer. There are a variety of sources for numerically produced entropy, including artificial viscosity or damping terms, round-off and truncation errors, and numerical instabilities. This article addresses the subject of establishing the entropy production of the natural processes. The determination, however, is not a straightforward task, in part, because the second law is usually formulated as an inequality. This difficulty is avoided by focusing on the rate of entropy production. In the first part of the analysis, the thermodynamic equations are formulated in an invariant form. In the final section, an equation is obtained in a nonsteady general coordinate system for the rate of entropy production. This equation is the authors' principle result.