An increase in drag was observed at Mach 0.6 which was attributed to the commencement of vortex shedding. At Mach 0.4, the flow of Novec™ 649 was in the shock-less regime and exhibited a pronounced dependency on the Reynolds number. The variation of drag coefficient over the Mach number range was comparable with literature data for ideal-gas compressible flow, including shock-less and intermittent shock wave, and permanent shock wave flows regimes. It was found that non-ideal gas effects did not strongly affect the overall drag. Changes in surface pressure distribution at higher subsonic velocities were identified and discussed. The new experimental data were compared with available literature results. This enabled in combination with the results for air an assessment of the impact of non-ideal gas dynamics on the form drag of a cylinder in the considered highly subsonic flow regime. Due to the charging of the wind tunnel, different values of the compressibility factor (0.876 < Z < 0.999) could be achieved for the organic vapor flow. Time-averaged pressure measurements gave information on surface pressure distributions, and the corresponding drag and base pressure drag coefficients were obtained. A circular cylinder was tested in the cross-flow of an organic vapor (Novec™ 649) and of air over the subsonic ( M < 0.4) and high subsonic (0.4 < M < 0.8) speed range in a continuously running pressurized closed-loop wind tunnel test facility.
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