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11:50
20 mins
3D FLUID DYNAMIC ANALYSIS OF A HIGH LOADED CENTRIFUGAL ROTOR FOR MINI ORC POWER SYSTEMS
Salvatore Vitale, Matteo Pini, Antonio Ghidoni, Piero Colonna
Session: Session 10: Turbine design II
Session starts: Tuesday 13 October, 10:30
Presentation starts: 11:50
Room: 1A Europe
Salvatore Vitale (Delft University of Technology)
Matteo Pini (Delft University of Technology)
Antonio Ghidoni (Universita' degli Studi di Brescia)
Piero Colonna (Delft University of Technology)
Abstract:
Organic Rankine Cycle (ORC) power systems are a well-established technology for the
conversion of thermal energy sources in the small-to-medium power range. In the last few
years, efforts have been devoted to the development of mini ORC (mORC) power systems (5-
30 kWe) for waste heat recovery from truck engines, or distributed conversion of
concentrated solar radiation. In these high-temperature applications the expander is arguably
the most critical component. Due to the high expansion ratio, turbo-expanders are typically
preferred.
Recently, a multi-stage radial-outflow turbine (ROT) configuration for ORC power systems
has been studied. However, even if the authors preliminarily demonstrated that ROT may
allow for compact and efficient expanders [1], some research questions are still open. Notably,
the key point is the fluid dynamic design of the first stages, which are subject to severe flow
conditions (very high flow deflection, low aspect ratio of the blades and with high tip
clearance losses).
This work thus proposes a novel design methodology for centrifugal cascades, specifically
targeted to the first rotor of the mORC centrifugal turbine described in Ref. [1].
Blades are initially designed using a novel in-house Turbomachinery Blade Modeler (BM),
then performance is verified by means of 3D CFD simulation on unstructured grids using the
solver SU2, recently extended also in-house to treat non ideal compressible fluid flows [2].
Results show that traditional blade design rules for axial cascades are not directly extendable
to centrifugal profiles and new design guidelines are needed. Moreover, the 3D performance
of the cascade has also been investigated by taking into account tip clearance and secondary
loss mechanisms. Finally, an accurate comparison with the mean-line code predictions is
provided.
As expected, the outcome of the study reveals moderate discrepancy between the CFD results
and the mean-line code. This suggests that in case of non-conventional machines a more tight
integration of design tools of increasing fidelity may be convenient.