An Inquiry Into the Aerodynamic and Aeromechanic Aspects of Next-Generation CO2-SO2 Power Turbines for Sustainable Applications: The Case of the Desolination Project

Abstract Over the past few years, the use of carbon dioxide and sulfur dioxide (CO2-SO2) mixtures as working fluids in transcritical and supercritical power cycles has gained significant interest, particularly for next-generation applications in small-scale plants. Operating with these mixtures can significantly reduce compression work while allowing for higher heat sink temperatures, thereby improving the overall cycle efficiency. In this context, the Desolination EU Horizon Project investigates the use of CO2-SO2 blends for power block in Concentrated Solar Power (CSP) plants. Investigating the turbine module aerodynamic and aeromechanical performance represents a key aspect to ensure optimal efficiency, and to verify the reliability of the power generation system in terms of mechanical integrity. Indeed, turbine blades characterized by small aspect ratio typically do not suffer from aeromechanical issues with conventional working fluids; however, the increased density of the CO2-SO2 mixture may present new challenges related to flow-structure interaction. This paper addresses these challenges through a numerical investigation of the Desolination power turbine, focusing on both aerodynamic and aeromechanical aspects. Steady and unsteady CFD analyses were performed by using the CFD TRAF code, an in-house solver developed at the University of Florence. From full-annulus multi-row unsteady simulation, the relevant forcing functions resulting from blade interactions were extracted via Discrete Fourier Transform (DFT). The aeromechanical analysis has also included the evaluation of the aerodynamic damping of all rotor rows using a nonlinear uncoupled approach. Forced response assessment, based on modal work computation, was finally performed to generate the frequency response curve of each blade row in both at resonance and out-of-resonance conditions.