Flow regimes in buoyancy-driven homogeneous variable-density turbulence

Abstract

In this chapter, we discuss density-ratio effects on the life cycle of buoyancy-driven homogeneous variable-density turbulence (HVDT) by using high-resolution (20483) Direct Numerical Simulations (DNS). Two density ratios 1.105 : 1 and 7 : 1 are considered for analysis. In HVDT, the acceleration field is applied to a triply periodic domain in which an initially heterogeneous mixture of two miscible, incompressible fluids with different densities are resting. The fluids start to move in opposite direction due to the differential buoyancy forces which generates turbulence. Meanwhile, the fluids molecularly mix which reduces the density difference, leading to weakening of the buoyancy forces. Turbulence dissipation overcomes turbulence production and VDT starts to decay. The life cycle of HVDT is divided into four different regimes based on turbulent kinetic energy evolution. Variations in the density ratio are found to significantly change the local evolution of the flow which is discussed using three-dimensional contours and the probability density functions of the vertical velocity.