Dynamics of inertial particles in a turbulent von Karman flow

TL;DR

This study investigates how neutrally buoyant particles of varying sizes behave in a turbulent von Karman flow, revealing size-dependent acceleration characteristics and differences from other turbulent flow types.

Contribution

It provides new insights into the size-dependent dynamics of inertial particles in VK flow, especially regarding acceleration autocorrelation and probability density functions.

Findings

Acceleration variance decreases with particle size as (D/eta)^-2/3

Acceleration autocorrelation time increases linearly with D/eta

Larger particles exhibit smaller wings in acceleration PDFs

Abstract

We study the dynamics of neutrally buoyant particles with diameters varying in the range [1, 45] in Kolmogorov scale units (eta) and Reynolds numbers based on Taylor scale between 580 and 1050. One component of the particles' velocity is measured using extended Laser Doppler Velocimetry at the center of a Von-Karman (VK) flow, acceleration is derived by differentiation. We find that although the particle acceleration variance decreases with increasing their diameter with scaling close to (D/eta)^-2/3, in agreement with previous observations, the characteristic time of acceleration autocorrelation increases much strongly than previously reported, and linearly with D/eta. A new analysis of the probability density functions of the acceleration shows smaller wings for larger particles; the flatness indeed decreases as also expected from the behavior of Eulerian pressure increments in the VK flow. We contrast our measurements with former observations in wind-tunnel turbulent flows and numerical simulations, and discuss if the observed differences arise from inherent properties of the VK flow.