Flow deviation and critical choking in transonic turbine cascades operating with non-ideal compressible flows

Francesco Tosto, Andrea Giuffré, Piero Colonna, Matteo Pini*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

In this work we examine the flow deviation and its relationship to critical choking, i.e., choking of the meridional component of velocity, in transonic turbine cascades operating with non-ideal compressible flows. To this purpose, a generalized expression of the corrected flow per unit area as a function of both the thermodynamic state and the molecular complexity of the working fluid, the Mach number, and the amount of swirl is derived. The trends of the corrected flow with respect to these quantities are used to infer physical insights on the flow deviation and on the operability of transonic turbine cascades in off-design conditions. Moreover, reduced-order models for the estimation of the flow deviation and the preliminary assessment of the losses have been developed and validated against the results of CFD simulations performed on a representative transonic turbine stator. Results suggest that flows of dense organic vapors exhibit larger deviations than those pertaining to compounds made of simple molecules, e.g., air. Furthermore, transonic turbines expanding dense vapors reach critical choking conditions at lower Mach numbers than the ones operating with simple molecules, and are affected by larger dissipation due to viscous mixing.

Original languageEnglish
Pages (from-to)181-199
Number of pages19
JournalJournal of the Global Power and Propulsion Society
Volume6
DOIs
Publication statusPublished - 2022

Keywords

  • choking
  • flow deviation
  • loss breakdown
  • non-ideal compressible fluid dynamics
  • Organic Rankine cycle
  • turbine

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