Proceedings of the ASME Turbo Expo 2014 GT2014 June 16-20, 2014, Dusseldorf, Germany GT2014-25475 A STUDY OF THE THREE-DIMENSIONAL UNSTEADY REAL-GAS FLOWS WITHIN A TRANSONIC ORC TURBINE Andrew P. S. Wheeler ∗ Faculty of Engineering and the Environment University of Southampton Southampton, UK Email: a.wheeler@soton.ac.uk Jonathan Ong GE Global Research Munich, Germany ABSTRACT In this paper we investigate the three-dimensional unsteady real-gas flows which occur within Organic Rankine Cycle (ORC) turbines. A radial-inflow turbine stage operating with supersonic vane exit flows (M ≈ 1.4) is simulated using a RANS solver which includes real-gas effects. Steady CFD simulations show that small changes in the inducer shape can have a significant ef- fect on turbine efficiency due to the development of supersonic flows in the rotor. Unsteady predictions show the same trends as the steady CFD, however a strong interaction between the vane trailing-edge shocks and rotor leading-edge leads to a significant drop in efficiency. NOMENCLATURE a acoustic speed C v specific heat at constant volume C p specific heat at constant pressure e internal energy h enthalpy k polytropic index l passage height M Mach number p pressure R radius s entropy T Temperature U blade tip speed V total velocity V r radial velocity V θ tangential velocity V x axial velocity ∗ Corresponding author. Greek letters α absolute flow angle β relative flow angle η isentropic efficiency Γ fundamental derivative Γ = 1 + ρ a  ∂ a ∂ρ  s ν jet speed ratio U /  2∆h o,s μ dynamic viscosity at stage inlet φ flow coefficient at rotor inlet V r /U ψ stage loading coefficient ∆h o /U 2 ρ density Subscripts abs absolute frame blade blade c critical point quantity exit stage exit in stage inlet m meridional o stagnation quantity rel relative frame s isentropic quantity tip at rotor leading-edge ts total-to-static tt total-to-total INTRODUCTION Organic Rankine Cycles (ORCs) are commonly used for heat recovery in power generation and industrial processes. ORCs are useful for generating power from low temperature heat sources. In order to increase the power density and therefore reduce costs, high pressure-ratio single-stage turbines operating with high molecular-weight working fluids are required. This 1 Copyright c  2014 by ASME