Spheres and fibers in turbulent flows at various Reynolds numbers

Abstract

We perform fully coupled numerical simulations using immersed boundary methods of finite-size spheres and fibers suspended in a turbulent flow for a range of Taylor-Reynolds numbers <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mn>12.8</a:mn><a:mo>&lt;</a:mo><a:msub><a:mi>Re</a:mi><a:mi>λ</a:mi></a:msub><a:mo>&lt;</a:mo><a:mn>442</a:mn></a:mrow></a:math> and solid mass fractions <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mn>0</b:mn><b:mo>≤</b:mo><b:mi>M</b:mi><b:mo>≤</b:mo><b:mn>1</b:mn></b:mrow></b:math>. Both spheres and fibers reduce the turbulence intensity with respect to the single-phase flow at all Reynolds numbers, with fibers causing a more significant reduction than the spheres. The particles' effect on the anomalous dissipation tends to vanish as <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>Re</c:mi><c:mo>→</c:mo><c:mi>∞</c:mi></c:mrow></c:math>. 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 fibers. Multifractal spectra of the near-particle dissipation show that spheres enhance dissipation in two-dimensional sheets, and fibers 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 fibers produce structures which completely overcome the turbulent vortex stretching behavior in their vicinity. Published by the American Physical Society 2024

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