In microflows where Reynolds number is much smaller than unity, screwing motion of spirals is an effective mechanism
of actuation as proven by microorganisms which propel themselves with the rotation of their helical tails. The main focus
of this study is to analyze the flow enabled by means of a rotating spiral inside a rectangular channel, and to identify
effects of parameters that control the flow, namely, the frequency and amplitude of rotations and the axial span between
the helical rounds, which is the wavelength. The time-dependent three-dimensional flow is modeled by Stokes equation
subject to continuity in a time-dependent deforming domain due to the rotation of the spiral. Parametric results are
compared with asymptotic results presented in literature to describe the flagellar motion of microorganisms.
Traveling plane-wave deformations on a solid thin film immersed in a fluid can create viscous propulsion in the direction
opposite to wave propagation. Here, we present modeling and analysis of a valveless dynamic micropump that
incorporates a traveling plane-wave actuator. Our numerical model incorporates direct coupling between solid deforming
boundaries and the fluid by means of a deforming mesh according to Arbitrary Lagrangian Eulerian implementation, and
2D unsteady Stokes equations to solve for the flow realized by the traveling-wave actuator in the channel. A commercial
finite-element package, COMSOL, is used for simulations. Analysis is carried out to identify the effects of operating
conditions such as wavelength, frequency and amplitude of the waves. For specified dimensions of the pump, maximum
time-averaged flow rate, exit pressure, rate-of-work done on the fluid and efficiency of the micropump are calculated for
different operating conditions.
Application of a low intensity axial magnetic field can promote significant convection during Bridgman growth of GeSi when resident thermoelectric currents at the growth interface are large due o difference of thermoelectric powers of the melt and of the crystal and the tangential temperature gradient at the interface. Thermoelectromagnetic convection (TEMC) in the GeSi melt is characterized by a meridional flow driven by the rotation of the fluid due to the azimuthal Lorentz force from currents in the radial direction, concentrated near the interface, and the axial magnetic field. A similar flow is caused by a rotating magnetic field (RMF). When the field is rotating sufficiently fast, a time-averaging azimuthal Lorentz force (almost uniform axially) causes a steady rotation of the melt, and an associated meridional convection (Ekman cells) near the interface. In this work, we developed a computational model to study convection of the GeSi melt in a microgravity environment in the presence of low intensity magnetic fields.