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Comparison of steady and unsteady rans CFD simulation of a supersonic ORC turbine
Benoit Obert, Paola Cinnella
Session: Session 3C: Turbomachinery (1)
Session starts: Wednesday 13 September, 16:30
Presentation starts: 17:10
Room: Building 27 - Lecture room 03

Benoit Obert (Enertime)
Paola Cinnella (Arts et M├ętiers ParisTech)

This article presents computational fluid dynamics (CFD) simulations of a supersonic flow inside an Organic Rankine Cycle turbine. The expander considered in this work is a single stage axial turbine using hexamethyldisiloxane (MM) as working fluid. The thermodynamic properties of the working fluid are modelled by a Helmoltz free energy based equation of state in both the design and simulation steps to accurately account for the non-ideal nature of the fluid under the considered conditions. The high expansion ratio of the turbine leads to a supersonic flow in the stator and rotor blade passages. The design of the stator and rotor blade shapes is carried out by means of the generalized method of characteristics. The CFD code used in this work is the commercial ANSYS CFX solver and the simulations are based on the two-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations supplemented by a k-omega turbulence model. Results provided by steady mixing plane simulations are compared to unsteady sliding mesh simulations to understand the implications of stator/rotor flow interaction on blade loading, torque, entropy generation and flow structure, at nominal and partial load.