Effect of a Turbulence Grid on the Compressible Flow of an Organic Vapor

Abstract The effect of a square-mesh wire grid on the compressible flow of an organic vapor was investigated, utilizing a closed-loop wind tunnel facility working with the fluid Novec 649 in the dilute gas regime. Due to its thermodynamic properties, this working fluid enabled hot-wire anemometry investigations while avoiding typical issues related to calibration and data reduction as usually observed in compressible flows. Due to the low speed of sound, the mean velocity level could be kept low, which was helpful regarding frequency resolution issues. The results of the experiments conducted under essentially incompressible flow conditions agreed well with the predictions of the turbulence theory, and a good level of isotropy was achieved downstream of the grid. With increasing flow Mach number, the anisotropy of the turbulence increased, and the isotropy was practically lost at flow Mach numbers in the range of the grid choking Mach number. The flow Mach number normalized by the grid choking Mach number was identified as a useful, primary variable for presenting the experimental data.