Preliminary design of an intermittent blowdown supersonic wind tunnel

The preliminary design for a mid-scale supersonic blowdown wind tunnel is presented in this study. The cross-sectional dimensions of the test section are determined to be 0.4 m by 0.4 m, and Mach 4 is the target maximum operational speed of the wind tunnel. The blowdown intermittent tunnel type was selected due to comparatively low built costs and its ability to operate at varying Reynolds numbers. First estimates are made in order to determine a run time of 60 seconds at Mach 4. The required inlet pressure to start the tunnel at Mach 4 is calculated to be roughly 15 bars, assuming that the output pressure is equal to atmospheric pressure at sea level. To enable a 60-second run time at Mach 4, a compressor with a maximum compression capacity of 40 bars feeding a series of tanks with total volumetric capacity of 40 𝑚^3 are chosen. The Method of Characteristics is implemented to develop the converging diverging nozzle geometry utilizing a code developed in MATLAB. Nozzle geometry is constructed by importing the contours' coordinates provided by the MoC approach into a computer-aided design program. Moreover, ANSYS Fluent 2023 R1 is used to confirm the nozzle geometry through both two-dimensional and three-dimensional CFD analyses. Meanwhile, mesh dependency study is performed to optimize the CFD analyses setup. The whole process is repeated for a different Mach number, Mach 2, to validate the methodology. The CFD study results indicate that there exists acceptable Mach number distribution uniformity at the exit border of the nozzles for both Mach 2 and Mach 4.