Steven C. Hart

Flow-Induced Resuspension of Rigid-Link Fibers from Surfaces

ABSTRACT Flow-induced removal of curly fibers from surfaces is studied. A generic rigid-link fiber model consisting of a chain of five ellipsoids with different orientations is developed, and used to study fiber resuspension in laminar and turbulent flows. The contact surfaces of the fiber with the wall are modeled as spherical joints. The hydrodynamic forces and torques acting on the ellipsoidal segments as well as the adhesion forces of nodes in contact with the surface are evaluated. Various possible modes of fiber detachment from the surface are identified, and the state of limiting equilibrium are analyzed. The critical velocities for detaching fibers of various sizes, orientations, and filament thicknesses are evaluated and discussed.

Detachment of rigid-link fibers with linkage contact in a turbulent boundary layer flow

Fiber removal with linkage contact in a turbulent boundary layer flow is studied. A rigid-link fiber model which is composed of two ellipsoids and one cylindrical link is considered. It is assumed that the fiber is in contact with the wall by the cylindrical linkage and a spherical end joint. The onset of rolling and sliding detachments is analyzed to determine the condition for removal of fibers from the surface. The hydrodynamic forces and torques acting on the fiber attached to a wall, along with the adhesion forces of contact node and linkage, are used in the model development. For different adhesion models, the minimum critical shear velocities for removing fibers of different sizes, orientations, and thicknesses are evaluated and discussed.

Electrostatic effects on resuspension of rigid-link fibers in turbulent flows

Abstract Fiber resuspension from smooth surfaces in a turbulent boundary layer flow including electrostatic effects is studied. A rigid-link fiber model which is composed of five rigidly attached ellipsoids is considered. The fiber contacts with the wall are modeled as spherical end joints. For an average of the Boltzmann charge distribution, as well as the saturation condition, the Coulomb, the image, the dielectrophoretic, and the polarization forces acting on the fiber in the presence of an imposed electric field are evaluated. The cases that charges are concentrated on the tip spherical joints, and when they are uniformly distributed along the ellipsoidal links are analyzed. The interfacial forces at the spherical contact points are determined by the Johnson–Kendall–Roberts (JKR) adhesion model. The theories of rolling and sliding detachment are used to study the onset of removal of fibers from surfaces in an air flow field. The hydrodynamic forces and torques acting on the fiber attached to a wall, along with the adhesion forces of contact nodes, are used in the model development. The minimum shear velocities needed to detach fibers of different sizes, orientations, and thickness from plane surfaces in the presence of an applied electric field are evaluated and discussed. It is shown, for saturation charge condition, the electric field strength significantly affects the critical velocity for removal of fibers from surfaces.