Characterization of coupling between inertial particles and turbulent wakes from porous disk generators

Kristin N Travis,Laure Vignal,Raúl Bayoán Cal,Martín Obligado,Henda Djeridi,Sarah E Smith,Mickaël Bourgoin

doi:10.1017/jfm.2021.1095

Abstract

This study presents the findings of a wind tunnel experiment investigating the behaviour of micrometric inertial particles with Stokes numbers around unity in the turbulent wake of a stationary porous disk. Various concentrations $\varPhi _{v}\in ([6-19] \times 10^{-6})$ of poly-disperse water droplets (average diameter 40–50 $\mathrm {\mu }$ m) are compared with sub-inertial tracer particles. Hot-wire anemometry, phase Doppler interferometry and particle image velocimetry were implemented in the near- and far-wake regions to study the complex dynamics of such particles. Quadrant analysis is used to explore the shear effects of the particle wake interaction. Turbulence statistics and particle size distributions reveal distinct differences in the structure of the wake when inertial particles are present in the flow. Additionally, there are different structures in the near and far wake regions and structures change with particle volume fraction.

Highlights

Many flows of interest in the natural environment and engineering applications combine turbulent wakes and inertial particles
This study explores the effects of inertial particles in the wake behind a stationary porous disk in homogeneous isotropic turbulence (HIT)
This study aims to characterize the behaviour of inertial particles in the axisymmetric turbulent wake of a porous disk

Summary

Introduction

Many flows of interest in the natural environment and engineering applications combine turbulent wakes and inertial particles. Lignarolo et al (2016) presented an experimental analysis comparing the near wakes of a wind turbine model and porous disk. The wakes behind porous disks have been studied as analogues to more complicated wakes such as parachutes and rotating wind turbines in single-phase flow applications. Their results establish a good match between the turbine and the disk for velocity, pressure and enthalpy fields, but show differences in turbulence intensity and turbulent mixing. The value of Reλ is greater in the wake due to greater σu of the turbulent signal In both cases λ decreases with increasing Reλ as higher velocities are producing more turbulence. Particle diameters and velocities were measured for water flow- rates of 1.7 and 2.0 l min−1 at the free-stream tunnel speeds listed in table 2, leading to particle volume fraction varying in the range Φv ∈ ([6 − 19] × 10−6)

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Discussion

Conclusion