Experimental and numerical flow investigation of a centripetal supersonic turbine for organic rankine cycle applications

The flow inside a new centripetal supersonic turbine for Organic Rankine Cycle (ORC) applications is investigated. The prototype achieved an isentropic internal efficiency of 64 %. Objectives of this work are the localization and reduction of losses inside the turbine. For this reason a numerical flow simulation is validated with measurements of the prototype. It can be concluded that the model implemented in ANSYS CFX 13.0 reproduces the flow realistically because the deviations of several significant quantities are within the experimental uncertainty. The rotor blades are modified and the supersonic flow deflection is corrected to increase the efficiency. In the numerical simulation the efficiency increases by changing the pitch-to-chord ratio, the flare angle and the flow angle at the outlet of the nozzle blades. The improvements yield a subsequently measured isentropic internal efficiency of about 79 % for the second series of the turbine type.