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Session: Parallel Session: Simulation and Design Tools
Session starts: Thursday 22 September, 11:10
Presentation starts: 11:50
Room: Auditorium

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David Pasquale (Università degli Studi di Brescia)
Antonio Ghidoni (Università degli Studi di Brescia)
Stefano Rebay (Università degli Studi di Brescia)

Abstract:
During the last decade, organic Rankine cycle (ORC) turbogenerators have become very attractive for the conversion of low-temperature heat sources in the small to medium power range. ORCs usually operate in thermodynamic regions characterized by high pressure ratios and strong real-gas effects in the flow expansion, therefore requiring a non-standard turbomachinery design. In this context, due the lack of experience, a promising approach for the design can be based on the intensive use of computational fluid dynamics (CFD) and optimization procedures to investigate a wide range of possible configurations. In this work an optimization strategy which aims to increase the performance of ORC turbines is presented. The capability of this strategy is demonstrated by analyzing an existing turbine, which is an impulse one-stage radial turbine where a strong shock appears in the stator channel due to the high expansion ratio. The goal of the optimization is to minimize the total pressure losses produced by the shock and to obtain a uniform anular flow at the stator discharge section, in terms of magnitude and direction of the flow velocity. To achieve this purpose, a global optimization method and a computational fluid dynamic solver are adopted. In particular, the optimization strategy is based on the coupling of a Genetic Algorithm with a surrogate-model (Kriging). The numerical solutions of the two-dimensional Euler equations are computed with the in-house built code zFlow [1]. The working fluid is toluene, whose thermodynamics properties are evaluated by an accurate equation of state, available in FluidProp [2]. The computational grids created during the optimization process have been generated through a fully automated 2D unstructured mesh algorithm based on the advancing-Delaunnay strategy [3].