Numerical Analysis of Aerodynamics and Performance of a Radial-Inflow Micro-ORC Turbine

Abstract

Organic Rankine Cycle (ORC) has proven to be an effective way to recover waste heat. The performance of ORC systems is profoundly affected by turbine selection, which is one of the most critical components. In this study, a numerical aerodynamic analysis of a micro-ORC turbine is carried out as an effort towards the formulation of a reduced order model (ROM) of the turbine for the dynamic simulation of the complete ORC system. The studied turbine is the radial-inflow turbine of the waste heat recovery micro-ORC test rig at the Laboratory of Fluid Dynamics, LUT University. The performance of the turbine, which features a highly supersonic flow at the stator outlet, is evaluated through steady-state CFD simulations of the complete turbine geometry using linear siloxane MDM (Octamethyltrisiloxane C8H24O2Si3) as working fluid. Results are discussed and compared with experimental data. Turbine efficiency is studied numerically at varying rotational speeds (25000-31000 rpm). A significant fluctuation in the flow angle at the stator is observed at low rotational speeds, while it decreases at higher speeds. At increasing rotational speed, the analysis shows a corresponding increase in the discharged flow rate, and the turbine efficiency up to 0.2061 kg/s and 79.3, respectively. Moreover, the flow features through the turbine nozzle ring and rotor blades are examined and discussed for selected operating conditions