Trailing edge losses constitute a substantial portion of the overall losses in transonic and supersonic turbines. These losses are significantly affected by the so-called base pressure, the pressure downstream of the blade trailing edge. The importance of accurately predicting this quantity in the turbine design has driven numerous experimental investigations aimed at developing appropriate correlations, mostly valid for ideal gases. However, technological limitations have hindered similar analyses for organic fluids. Aiming to provide a foundational basis for addressing this issue, this paper presents the preliminary phase of a numerical investigation of the base pressure problem in supersonic non-ideal flows. The study utilizes the DNS code 3DNS, focusing on conditions representative of organic Rankine cycle applications, choosing the siloxane MM as the working fluid. This paper details the setup of the numerical investigation, including the definition of the numerical domain and working conditions. A preliminary RANS analysis is conducted to examine the effects of the Reynolds number on the generated flow field and to provide an initial solution for initializing the DNS simulations. Finally, the first results from DNS are reported, highlighting the main findings and outlining the next steps for this investigation.