Analysis of the moist air transonic flow in the symmetric and asymmetric nozzle of the low expansion

Abstract

Condensation has a negative impact on turbomachinery efficiency in many energy processes. This paper compares the expansion of moist air in symmetric and asymmetric nozzles with a low expansion rate. The presented numerical study is supported by analytical and experimental research. The experimental tWesting was carried out using an in-house experimental test rig where two nozzles were examined for moist air with relative humidity of about 25%. The nozzles were tested for a supersonic outlet, as well as for the outlet condition with elevated pressure, which resulted in the occurrence of a normal shock in the test section. The asymmetric nozzle profile is congruent with the symmetric nozzle. However, the nozzle walls are shifted linearly in the flow direction. The Schlieren photography technique and static pressure measurements on the nozzle wall were used for qualitative identification of both condensation and shock waves. The presented numerical modelling was conducted using commercial computational fluid dynamics software extended with an in-house condensation model. The code was validated against in-house experiment as well as against the data available in the literature. The analysis of the flow in the considered two types of nozzles with a very low expansion rate revealed very interesting structures of pressure waves. The impact of the linear shift of the nozzle walls on the condensation process and the interaction of the condensation wave with aerodynamic oblique as well as normal shock waves were investigated.