Decaying versus stationary turbulence in particle-laden isotropic turbulence: Turbulence modulation mechanism

Abstract

The objective of the current paper is to clarify the physical distinction between turbulence modulations by laden particles in decaying isotropic turbulence and stationary isotropic turbulence. Direct numerical simulations of stationary and decaying isotropic turbulence were carried out using 1283 grid points at a Taylor micro-scale Reynolds number of Rλ ∼ 70. The effect of O(106) solid particles with a different Stokes number (St) was implemented as a point-force approximation in the Navier-Stokes equation. Turbulent kinetic energy, acceleration, enstrophy, strain rate, and various spectra were examined to determine the distinctions. Turbulence modulation in decaying turbulence is qualitatively and quantitatively inconsistent compared to that in stationary turbulence, particularly when the particles have St ≤ 1, mainly due to the artificial forcing necessary for stationary status. For the particles with St > 1, however, decaying and stationary turbulence are qualitatively similar. A simple analysis confirms that stationary turbulence is not appropriate for the study of turbulence modulation by particles with St ≤ 1. Furthermore, the injection perturbation of particles has a significant effect on turbulence modulation in decaying turbulence. An investigation of the correlation between turbulence field zones and the two-way interaction energy was conducted to gain a better understanding of the modulation mechanism.