TY - JOUR
T1 - Flow deviation and critical choking in transonic turbine cascades operating with non-ideal compressible flows
AU - Tosto, Francesco
AU - Giuffré, Andrea
AU - Colonna, Piero
AU - Pini, Matteo
PY - 2022
Y1 - 2022
N2 - 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.
AB - 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.
KW - choking
KW - flow deviation
KW - loss breakdown
KW - non-ideal compressible fluid dynamics
KW - Organic Rankine cycle
KW - turbine
UR - http://www.scopus.com/inward/record.url?scp=85136319283&partnerID=8YFLogxK
U2 - 10.33737/jgpps/151659
DO - 10.33737/jgpps/151659
M3 - Article
AN - SCOPUS:85136319283
SN - 2515-3080
VL - 6
SP - 181
EP - 199
JO - Journal of the Global Power and Propulsion Society
JF - Journal of the Global Power and Propulsion Society
ER -