Design methodology for supersonic radial vanes operating in non-ideal flow conditions

The stator vane of high-temperature Organic Rankine Cycle radial-inflow turbines operates under severe expansion ratios and the associated fluid-dynamic losses account for nearly two-third of the total losses generated inside the machine. The efficiency of the machine can strongly benefit from specialized high-fidelity design methods able to provide shapes attenuating shock wave formation. Shape optimization is certainly a viable option to deal with supersonic ORC stator design, but it is computationally expensive and often case specific. In this work, a robust method to approach the problem in a more systematic manner is documented. The methodology involves an optimization procedure encompassing the method of characteristics extended to non-ideal fluid flow for profiling the diverging part of the nozzle. The subsonic section and semi-bladed suction side are retrieved using a simple conformal geometrical transformation. The method is applied to the design a supersonic ORC stator working with Toluene vapors, for which two blade shapes were already available. The comparison of fluid-dynamic performance clearly indicates that the MoC-Based method is able to provide the best results with the lowest computational effort, and is suitable to be used to draw general design guidelines