The computation of the entropy generation rate for turbomachinery design applications: some theoretical remarks and practical examples

Abstract

The calculation of the entropy generation rate dS/dt in turbomachinery passages is a relatively easy task, once the velocity and temperature fields are known in detail. The global entropy generation rate is directly related to the cascade efficiency, but its functional dependence on the local characteristics of the flowfield is not immediately detectable. On the contrary, knowledge of the local entropy generation rate at each point in a channel provides immediate useful insight into the relative importance of the different sources of irreversibility in the process. This paper presents a rational derivation of the relationships between the local and global entropy generation and the local features of the flow, and illustrates them by means of some examples derived from applications developed in the last decade by the Turbomachinery Group of the University of Roma 1. The merits and limits of the use of such a 'local' the development of an inverse design approach is proposed.