Lattice–Boltzmann simulations for analysing the detachment of micron-sized spherical particles from surfaces with large-scale roughness structures (Open Access)--颗粒学报PARTICUOLOGY

Cui, Y., & Sommerfeld, M. (2022). Lattice–Boltzmann simulations for analysing the detachment of micron-sized spherical particles from surfaces with large-scale roughness structures. Particuology, 61, 47-59. https://doi.org/10.1016/j.partic.2021.05.004

Lattice–Boltzmann simulations for analysing the detachment of micron-sized spherical particles from surfaces with large-scale roughness structures (Open Access)

Yan Cui ^a, Martin Sommerfeld ^b *

a School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
b Multiphase Flow Systems, Institute of Process Engineering, Otto-von-Guericke-University Magdeburg, Hoher Weg 7b, D-06120 Halle (Saale), Germany

10.1016/j.partic.2021.05.004

Volume 61, February 2022, Pages 47-59

Received 4 February 2021, Revised 1 April 2021, Accepted 4 May 2021, Available online 28 May 2021, Version of Record 27 October 2021.

E-mail: martin.sommerfeld@ovgu.de

Highlights

• Fluid forces on spherical particles attached to a large-scale wall roughness structure.

• High-resolution Lattice–Boltzmann simulation with local grid refinement.

• Model roughness made of homogeneously distributed rows of semi-cylinders.

• Drag and lift strongly depends on the geometry of asperity structure.

• Estimation of detachment probability showed sliding is mostly occurring.

Abstract

Fully resolved numerical simulations of a micron-sized spherical particle residing on a surface with large-scale roughness are performed by using the Lattice–Boltzmann method. The aim is to investigate the influence of surface roughness on the detachment of fine drug particles from larger carrier particles for transporting fine drug particles in a DPI (dry powder inhaler). Often the carrier surface is modified by mechanical treatments for modifying the surface roughness in order to reduce the adhesion force of drug particles. Therefore, drug particle removal from the carrier surface is equivalent to the detachment of a sphere from a rough plane surface. Here a sphere with a diameter of 5 μm at a particle Reynolds number of 1.0, 3.5 and 10 are considered. The surface roughness is described as regularly spaced semi-cylindrical asperities (with the axes oriented normal to the flow direction) on a smooth surface. The influence of asperity distance and size ratio (i.e. the radius of the semi-cylinder to the particle radius, Rc/Rd) on particle adhesion and detachment are studied. The asperity distance is varied in the range 1.2 < L/R_d < 2 and the semi-cylinder radius between 0.5 < R_c/R_d < 0.75. The required particle resolution and domain size are appropriately selected based on numerical studies, and a parametric analysis is performed to investigate the relationship between the contact distance (i.e. half the distance between the particle contact points on two neighbouring semi-cylinders), the asperity distance, the size ratio, and the height of the particle centroid from the plane wall. The drag, lift and torque acting on the spherical particle are measured for different particle Reynolds numbers, asperity distances and sizes or diameters. The detachment of particles from rough surfaces can occur through lift-off, sliding and rolling, and the corresponding detachment models are constructed for the case of rough surfaces. These studies will be the basis for developing Lagrangian detachment models that eventually should allow the optimisation of dry powder inhaler performance through computational fluid dynamics.

Graphical abstract

Keywords

Lattice–Boltzmann method; Fully-resolved simulations; Particle detachment; Surface roughness; Semi-cylindrical asperities; Particle detachment model

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