Experimental Characterization of Inertial Range Statistics in Compressible Turbulence

Compressible turbulence has applications to astrophysical fluid dynamics, high-speed civil transport, and combustion. For compressible subsonic flows, large turbulent fluctuations can generate randomly distributed regions of local vigorous fluid compression.  Measurements are necessary to further develop physical models that quantify the influence of compressibility on turbulent flows. In our experiments, we fabricated nanoscale hot wire probes inspired by Vallikivi et al. (J. Microelectromech. Syst., 2014) using semiconductor manufacturing techniques, and measured turbulence in a specialized pressure vessel filled with sulfur hexafluoride gas. With the use of smaller than conventional hot-wire probes, we resolve inertial range statistics. The dense gas sulfur hexafluoride makes it possible to reach high Mach numbers due to its lower speed of sound compared to air, and high Reynolds numbers since we can lower its kinematic viscosity by an order of magnitude with pressure adjustments. We report measurements of turbulence statistics as well as power spectra for turbulent Mach numbers up to 0.3, and for Taylor microscale Reynolds numbers between 200 and 3700.