Variation of density gradient statistics with Mach number in compressible turbulence

The study of compressible behaviors in turbulence is used in various areas such as astrophysical flows, detonations, and scramjet engine combustion. The interactions of the eddies generate large velocity, pressure, and temperature gradients, and ultimately density gradients in the flow. Simulations show that the variance of density fluctuations in compressible turbulence is proportional to the Mach number to the 4^th power. We explored density variations experimentally using a fan-generated jet in a pressurized vessel. The speed of sound in the vessel can be adjusted using different gases including sulfur-hexafluoride (SF₆) to increase the turbulent Mach number up to 0.15 while holding the Taylor-Reynolds number constant at values up to 1000. To measure density gradients, we used quantitative schlieren imaging with a high-speed camera. In addition to the visualization of the turbulence in our facility, we analyzed the data temporally to calculate density gradients statistics. We observed an increase in the density gradient variance with Mach number akin to simulated results.