Particle removal from rough surfaces

Particle resuspension from surfaces in turbulent flow became in recent years the object of many theoretical and experimental studies. In general, available experimental data do not support the existing theoretical models.The main objective of the present work is to analyze the role of roughness in resuspension. We show that particle detachment from rough surfaces may be caused by the hydrodynamic moment determined by shear viscous sublayer with additional effects of turbulent structures. A particle in contact with one, two, or three surface asperities is considered. We show that a one-asperity contact is similar to the contact of a particle with a smooth surface, but the detaching moment is reduced both by the reduced adhesion force and by the reduced contact radius. For a particle in contact with two asperities there exist two main possibilities of detachment by rotation, namely, along the line connecting the contact points, and along the line normal to the first one. The analysis shows that the second possibility is preferable, except for the case where the asperities are very close to each other. Finally, we consider a particle in contact with three asperities and show that the motion in this case is a combination of the two possibilities listed above.The analysis of experimental data from the literature shows that values of the hydrodynamic moments are comparable to their possible surface counterparts, while the hydrodynamic lift force remains smaller than the adhesion force by several orders of magnitude. The experimental results can often be explained considering roughness for a variety of surfaces.