The validation of SU2 for modelling classical non-ideal compressible fluid dynamics will advance the research into efficient ORC turbomachinery design. This study determines the validity of the two-dimensional flow solver for predicting the isentropic expansion of Siloxane MM through a converging-diverging nozzle using compressible Euler equations, adiabatic flow, and the Peng-Robinson equation of state. Two flows with an inlet stagnation temperature of 525K were considered: an expansion from 18.4 bar to 2.1 bar, and an expansion from 11.1 bar to 1.3 bar.  Mach number along the centreline and static pressure along the nozzle surface were used as the direct system response quantities used in the analysis. Experimental data and uncertainty came from the ORCHID, model input uncertainty was quantified using stochastic collocation, and the numerical uncertainty was calculated using the Richardson extrapolation. The conclusions were based on a hybrid of the ASME V&V 20 and Real Space validation metrics, with a novel Engineering Response Quantity analysis based on determining the effects of system uncertainty on performance parameters. The studied SU2 model provide valid predictions for Mach number, and invalid predictions for static pressure. The largest error is in the kernel region, where E_Mach=0.111 and E_Pressure = 112 kPa. Mach number has a maximum simulation uncertainty of 2% at the transition to the reflex region. Pressure has a maximum uncertainty of 3% at the throat. In the context of turbomachinery the simulation uncertainties translate to +/-0.001 and +/-0.02 on a loss coefficient calculated across a theoretical normal shock, for Mach and pressure respectively. Considering +/-0.01 as significant for a loss coefficient the Mach uncertainty is negligible. Input uncertainty is the largest component of the pressure uncertainty, while experimental uncertainty is dominant for Mach. The input parameters which provide the highest contribution to the uncertainty are critical pressure and temperature. The developed infrastructure can be used for expanding the validation of SU2 to different flow cases.