Dynamics of finite-size spheroids in turbulent flow: the roles of flow structures and particle boundary layers

Abstract

We study the translational and rotational dynamics of neutrally buoyant finite-size spheroids in hydrodynamic turbulence by means of fully resolved numerical simulations. We examine axisymmetric shapes, from oblate to prolate, and the particle volume dependences. We show that the accelerations and rotations experienced by non-spherical inertial-scale particles result from volume filtered fluid forces and torques, similar to spherical particles. However, the particle orientations carry signatures of preferential alignments with the surrounding flow structures, which are reflected in distinct axial and lateral fluctuations for accelerations and rotation rates. The randomization of orientations does not occur even for particles with volume-equivalent diameter size in the inertial range, here up to $60$ dissipative units ( $\eta$ ) at Taylor-scale Reynolds number ${Re_{\lambda }=120}$ . Additionally, we demonstrate that the role of fluid boundary layers around the particles cannot be neglected in reaching a quantitative understanding of particle statistical dynamics, as they affect the intensities of the angular velocities and the relative importance of tumbling with respect to spinning rotations. This study brings to the fore the importance of inertial-scale flow structures in homogeneous and isotropic turbulence and their impacts on the transport of neutrally buoyant bodies with sizes in the inertial range.

Numerical study on turbulence modulation of finite-size particles in plane-Couette flow

“…In this subsection, we describe briefly the numerical schemes used to simulate the particle suspension. The turbulence is solved numerically using an open-source code with the lattice Boltzmann method, the ch4-project (Calzavarini 2019), which has been validated extensively in particle-laden turbulence both for point-like particles (Mathai et al 2016;Jiang et al 2021) and finite-size particles (Jiang et al 2020(Jiang et al , 2022. The code was validated by comparing the translational dynamics of spheres at Re λ = 32 with a previous reference study (Homann & Bec 2010).…”

“…The code was validated by comparing the translational dynamics of spheres at Re λ = 32 with a previous reference study (Homann & Bec 2010). The details and validations of the code can be found in our previous work (Jiang et al 2022).…”

“…For particles with higher volume fractions or non-negligible inertia, the interactions between particle and fluid can be modelled as two-way coupling using the point-particle method towards the motivation of investigating the particle dynamics and flow modulations (see the literature in the reviews Voth & Soldati 2017;Brandt & Coletti 2022). However, given its simplicity, the point-particle model could not account precisely for the feedback of particles on the surrounding flows in general situations, such as the particle boundary layer and the wake behind it (Jiang et al 2022). To this end, the finite-size particles, typically with diameters larger than the dissipation length scale η of the surrounding turbulent flows (Voth & Soldati 2017;Mathai et al 2020;Brandt & Coletti 2022), have been a vigorous field in recent years, in both experiments (Qureshi et al 2007(Qureshi et al , 2008Fiabane et al 2012;Will et al 2021;Will & Krug 2021a,b;Obligado & Bourgoin 2022) and numerical simulations (Calzavarini et al 2009;Picano, Breugem & Brandt 2015;Peng, Ayala & Wang 2020;Yousefi, Ardekani & Brandt 2020;Assen et al 2022;Demou et al 2022;Li, Xia & Wang 2022).…”

“…To this end, the finite-size particles, typically with diameters larger than the dissipation length scale η of the surrounding turbulent flows (Voth & Soldati 2017;Mathai et al 2020;Brandt & Coletti 2022), have been a vigorous field in recent years, in both experiments (Qureshi et al 2007(Qureshi et al , 2008Fiabane et al 2012;Will et al 2021;Will & Krug 2021a,b;Obligado & Bourgoin 2022) and numerical simulations (Calzavarini et al 2009;Picano, Breugem & Brandt 2015;Peng, Ayala & Wang 2020;Yousefi, Ardekani & Brandt 2020;Assen et al 2022;Demou et al 2022;Li, Xia & Wang 2022). In particular, by numerically implementing no-slip boundary conditions on their surface, the finite-size particles are capable of modelling the particle dynamics Jiang et al 2022) and the resulting turbulence modulation (Ardekani et al 2017;Wang, Sierakowski & Prosperetti 2017b;Ardekani & Brandt 2019).…”

“…One of the subjects of particle-laden turbulence in the non-dilute regime is the turbulence modulation caused by particles. Due to the no-slip boundary conditions at their surface, the finite-size particles could modulate the surrounding flow and the entire field, such as through shedding vortices in the wake region (Risso 2018;Mathai et al 2020) and enhancing the dissipation rate around them (Jiang et al 2022). For particle-laden turbulence with neutrally buoyant particles, the system can be characterized by four dimensionless numbers, namely, the flow Reynolds number Re, the size ratio of particle diameter to turbulence dissipation length scale d v /η, the aspect ratio of particles λ, and the volume fraction of particles φ.…”