Spheres and fibres in turbulent flows at various Reynolds numbers

Abstract

We perform fully coupled numerical simulations using immersed boundary methods of finite-size spheres and fibres suspended in a turbulent flow for a range of Taylor Reynolds numbers $12.8<Re_\lambda<442$ and solid mass fractions $0\leq M\leq1$. Both spheres and fibres reduce the turbulence intensity with respect to the single-phase flow at all Reynolds numbers, with fibres causing a more significant reduction than the spheres. The particles' effect on the anomalous dissipation tends to vanish as $Re \to \infty$. A scale-by-scale analysis shows that both particle shapes provide a "spectral shortcut" to the flow, but the shortcut extends further into the dissipative range in the case of fibres. Multifractal spectra of the near-particle dissipation show that spheres enhance dissipation in two-dimensional sheets, and fibres enhance the dissipation in structures with a dimension greater than one and less than two. In addition, we show that spheres suppress vortical flow structures, whereas fibres produce structures which completely overcome the turbulent vortex stretching behaviour in their vicinity.