Design and analysis of an axial turbine for high-temperature organic Rankine cycle

Abstract

The organic Rankine cycle (ORC) system is of great importance to achieving the effective exploitation of waste energy. As the essential component of the ORC system, the expander is directly related to the performance and structure size of the ORC system, which deserves to be studied in detail. A single-stage axial turbine with a U-shaped volute is presented for the high-temperature ORC system in this paper. Based on preliminary design and modeling, the turbine aerodynamic performance under design and off-design conditions is investigated in numerical simulation. Results show that the turbine efficiency is 77% with a pressure ratio of 4.78 at the design point and the turbine efficiency can still be maintained above 70% as the pressure ratio reaches 6. It can be concluded that low Reynolds number flow and negative incidence angle are the main reasons for low turbine efficiency under the low pressure ratio, while the shock wave becomes the key factor influencing turbine efficiency under the high pressure ratio. In addition, blade profile optimization and shock wave management is the primary way to maintain high turbine efficiency under a high pressure ratio. Results indicate that the turbine proposed in this paper is proven suitable for high-temperature ORC systems and the relevant research has a certain guiding value for the efficient and compact single-stage axial turbine design.