Designing structured surfaces that repel fluid-borne particles

Using computational modeling, we examine particle-laden flows along surfaces decorated with periodic arrays of tilted posts. We show that when high-aspect-ratio posts are tilted against the flow direction, cross-stream circulatory secondary flows emerge. These circulatory flows enhance the net lift force acting on finite-sized particles transported by fluid, thereby repelling the particles from the wall and preventing their deposition. This hydrodynamic effect can potentially be used for designing antifouling and self-cleaning surfaces.

Figure 1

Schematic of computational setup.

Figure 2

Particle trajectories for particles with different dimensionless external forces $W$ in posted microchannels and in a microchannel with smooth walls. Particle radius is $R=0.25L$ and it is initially located at $y=0.167L_y$ and $z=0$.

Figure 3

Period-averaged cross-stream velocity (a) in a microchannel with posts normal to the bottom wall, and (b) in a microchannel with posts tilted ${45}^{\circ }$ against the flow direction. The dotted lines show the contours of the surface posts. The arrows show the magnitude and direction of the averaged flow velocity. The colors (grayscale) indicate the magnitude of the dimensionless flow vorticity.

Figure 4

Equilibrium positions of particles with $R=0.25L$ and $W=8.37$ in a channel with posts tilted ${45}^{\circ }$ against the flow direction. The equilibrium positions are calculated by averaging particle trajectories over one structure period in the $x$ direction. The dotted lines show the location of surface posts.

Figure 5

Cross-stream trajectories of particles with different $W$. Particle radius is $R=0.25L$.

Figure 6

Dimensionless critical force $W_{cr}$ as a function of particle radius $R$ in channels with posted and smooth walls. The inset shows the ratio between critical forces in posted and smooth channels.

Figure 7

Equilibrium positions of particles with $R=0.25L$ and $z=0$ in channels with posts with different tilt angle $\alpha$.