ABSTRACT
As discussed in previous chapters, entropy provides a valuable design tool for analyzing performance of fluid engineering systems and designing alternatives that improve energy efficiency. This book has been primarily focusing on local entropy tracking within individual components of a system, while other authors such as Rosen and Dincer (1999) have developed comprehensive methods of overall exergy analyses of a system. This chapter focuses on the role of entropy and the Second Law of Thermodynamics in numerical simulations, particularly involving error indicators for computational fluid dynamics (CFD). Entropy indicates the degree of molecular chaos or randomization, and this disorder can be interpreted in a physical sense (a traditional view), as well as a computational sense (a more recent view). The traditional view may be traced back to pioneering developments by the German mathematical physicist, Rudolf Clausius, in 1850, on the importance of entropy in steam engine performance. Computational modeling of entropy has arisen more recently with the advent of digital computers. It relates entropy and the Second Law with discretization errors (Naterer and Schneider, 1987), artificial dissipation (Hughes et al., 1986), and nonphysical numerical results (Majda and Osher, 1979). This chapter will focus on numerical errors, whereas the following chapter will describe the role of entropy and the Second Law in solution uniqueness and numerical stability of CFD simulations.
