Abstract
An overview is presented of the recent developments in the application of large eddy simulation (LES) for prediction and analysis of local entropy generation in turbulent reacting flows. A challenging issue in such LES is subgrid-scale (SGS) modeling of filtered entropy generation terms. An effective closure strategy, recently developed, is based on the filtered density function (FDF) methodology with inclusion of entropy variations. This methodology, titled entropy FDF (En-FDF), is the main focus of this article. The En-FDF has been introduced as the joint velocity-scalar-turbulent frequency-entropy FDF and the marginal scalar-entropy FDF. Both formulations contain the chemical reaction and its entropy generation effects in closed forms. The former constitutes the most comprehensive form of the En-FDF and provides closure for all of the unclosed terms in LES transport equations. The latter is the marginal En-FDF and accounts for entropy generation effects, as well as scalar-entropy statistics. The En-FDF methodologies are described, and some of their recent predictions of entropy statistics and entropy generation in turbulent shear flows are presented.
Highlights
Optimum use of energy is a major concern in designing modern energy conversion systems.According to the second law of thermodynamics, the energy efficiency in practice is always less than that expected theoretically, because of the irreversibilities in the system
In recent works [63,64], a methodology based on filtered density function (FDF), termed the entropy FDF (En-FDF), has been introduced, which allows large eddy simulation (LES) prediction of entropy transport and generation in turbulent reacting flows
The objective of this paper is to provide an overview of the state of progress in the application of En-FDF for LES prediction of entropy generation
Summary
Optimum use of energy is a major concern in designing modern energy conversion systems. In recent works [63,64], a methodology based on filtered density function (FDF), termed the entropy FDF (En-FDF), has been introduced, which allows LES prediction of entropy transport and generation in turbulent reacting flows. This methodology has been presented as two formulations: the comprehensive and the marginal. This methodology is computationally more affordable and, constitutes a more practical means of predicting entropy generation in complex turbulent reacting flows It requires closure for all of the second order SGS moments via the conventional (non-FDF) LES models.
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