Experimental characterization of organic vapor flows in asymmetric curved supersonic nozzles

An experimental campaign investigated the supersonic expansion of linear siloxane MM (hexamethyldisiloxane, C 6 H 18 OSi 2 ) in asymmetric curved planar nozzles. Two benchmark nozzle geometries were tested, both designed to discharge a parallel uniform flow of MM at Mach 1.6 under reservoir conditions characterized by a compressibility factor Z t = 0 . 40 . The nozzles feature gently-curved mean lines from inlet to outlet, discharging flow at geometric deviations of 6 ° and 17 ° from the horizontal. They differ in the shape of the channel near the minimum-area section (throat), with the first nozzle exhibiting upper and lower contours of opposite curvature, while the second nozzle has contours of concordant curvature. Shock-free expansions were observed under all tested conditions, ranging from highly nonideal ( Z t = 0 . 41 ) to ideal-like ( Z t = 0 . 95 ). Total pressure, temperature, static pressures from the inlet to the outlet, and schlieren images were recorded for each condition. A novel optical method, recently developed for asymmetric flows, enabled Mach number measurements without prior knowledge of the flow direction. The tested geometries mimic converging-diverging blade passages with a curved mean line. This study provides the first experimental validation of these asymmetric designs, previously introduced and verified only through CFD. The resulting dataset offers a valuable benchmark for validating numerical design and analysis tools in nonideal compressible flows, with direct relevance to the design of supersonic ORC turbine stages. • Nonideal flows in asymmetric curved planar nozzles are tested experimentally. • Supersonic expansions of MM are measured under various nonideal flow conditions. • Mach number and static-to-total pressure ratio trends reveal clear nonideal effects. • Experiments agree with simulations in Mach number and pressure ratio trends. • Blade-like nozzle shapes support turbomachinery design and validation.