Enhancement of thermal mixing under supercritical condition by increasing shear rate

•Direct Numerical Simulation for turbulent mixing layer at supercritical pressure.•Improvement of vortical structures by increasing shear rate.•Enhancement of thermal mixing due to the entrainment of vortical structures.•Energy spectra of velocity and temperature for mixing layer are concluded. The dynamical characteristics of the shear-driven mixing layer can be inhibited due to the variations in fluid density. In this work we expect to address this issue by increasing shear rate. Direct numerical simulations of mixing layer between two streams with different temperatures at supercritical pressure are conducted. We confirm that the turbulent characteristics of mixing layer are inhibited with increasing density ratio between the lower and upper streams, resulting in the destruction of large-scale vortex, especially at the high-density side. By increasing the velocity ratio between the two streams, however, the mixing performance is enhanced with regeneration of the hairpin vortex due to increase in mean shear. The enstrophy production thus increases due to enhancement of vortex stretching and the thermal mixing efficiency is enhanced due to the entrainment of vortical structures. Further, the streamwise spectra of the temperature fluctuations follow a slope of −3 in the viscous-diffusive range.