This article demonstrates various aspects of polytropic efficiency calculations method for performance simulation of gas turbines. A recursive algorithm for integrating the incremental classic definition can easily be derived in a manner that any equations of state v(p, T) can be used. The Constant Dissipation Rate Algorithm (CDRA) is recommended for all calculations of polytropic changes with elevated accuracy requirements but especially if high pressure or pronounced real gases are involved. All required formulas are indicated in the paper. There is also a simple test for the achievable convergence or accuracy included. The comparison of the CDRA with two conventional formulas indicates astonishing deviations even for dry air.
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Wettstein, H. E.: “Polytropic Change of State Calculations”, IMECE2014-36202
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