Statistics of density gradients in compressible turbulence using quantitative schlieren imaging

Direct numerical simulations show shock-like structures at turbulent Mach numbers as low as 0.1. Quantifying the conditions that generate these structures is key to understanding their role in natural and engineered settings. In a pressurized vessel, we adjust the speed of sound using different gases including SF₆ in order to increase the turbulent Mach number up to 0.15 while holding the Taylor-Reynolds number constant, up to 1000. In this way, we can distinguish between the role of the Reynolds number and Mach number in the development of extreme events. Schlieren imaging reveals density gradients in a turbulent jet, which we quantify by implementing a weak calibration lens. Analyzing the time-varying signals from single pixels of a high-speed camera, we compare the temporal energy spectra and distributions with simulation results from literature. We then present the first visualizations of the turbulent flow and statistics of the density gradient fluctuations at various Mach and Reynolds numbers.