Turbulence characteristics along the path of a heavy particle

Abstract

The turbulence along the path of a particle in an isotropic turbulent flow is investigated using direct numerical simulation. The turbulence is simulated using a collocation spectral method on an equi-spaced three-dimensional grid of 128 3 points with a Taylor micro-scale Reynolds number of 65. The particulate phase is treated as a simple system where the flow is not affected by the presence of the particles. A total of 8192 particles are tracked through the flow using a Lagrangian advancement scheme with Stokes drag as the only force applied to the particles. The implementation of the forcing method used to maintain a constant level of kinetic energy within the flow is studied. The total fluid turbulence kinetic energy was found to be a function of particle Stokes number with smaller particles (St<1) seeing slightly higher average velocity fluctuations than a Lagrangian average of the turbulence and intermediate particles (1<St<10) seeing slightly lower average fluctuations. Likewise, the turbulence integral time scales of the fluid along the path of a particle appear slightly larger than both the Eulerian and Lagrangian integral time scales for these intermediate particles. All preferentially concentrated particles (0.1<St<10) saw a lower average vorticity and higher deformation of the fluid than a volume average of the turbulence. The preferential concentration of the particles peaked at a Stokes number of 1 with particles being on average 20% closer to the nearest neighboring particle than in a randomly distributed case. These data suggest that it is the vorticity measured along the path of a particle which is the dominant factor for variations of statistical properties in the particle Lagrangian reference frame.