This review summarizes recent experimental studies of instabilities in free-surface flows driven by thermocapillarity. Two broad classes are considered, depending upon whether the imposed temperature gradient is perpendicular (Marangoniconvection instability) or parallel (thermocapillary-convection instability) to the free surface. Both steady and time-dependent instabilites are reviewed in experiments employing both large-and small-aspect-ratio geometries of various symmetries.

Combined thermocapillary–buoyancy convection in a thin rectangular geometry is investigated experimentally, with an emphasis on the generation of hydrothermal-wave instabilities. For sufficiently thin layers, pure hydrothermal waves are observed, and are found to be oblique as predicted by a previous linear-stability analysis (Smith & Davis 1983). For thicker layers, both a steady multicell state and an oscillatory state are found to exist, but the latter is not in the form of a pure hydrothermal wave.

A novel method is developed to simulate suspensions of deformable particles by coupling the lattice-Boltzmann method (LBM) for the fluid phase to a linear finiteelement analysis (FEA) describing particle deformation. The methodology addresses the need for an efficient method to simulate large numbers of three-dimensional and deformable particles at high volume fraction in order to capture suspension rheology, microstructure, and self-diffusion in a variety of applications. The robustness and accuracy of the LBM-FEA method is demonstrated by simulating an inflating thinwalled sphere, a deformable spherical capsule in shear flow, a settling sphere in a confined channel, two approaching spheres, spheres in shear flow, and red blood cell deformation in flow chambers. Additionally, simulations of suspensions of hundreds of biconcave red blood cells at 40 % volume fraction produce continuum-scale physics and accurately predict suspension viscosity and the shear-thinning behaviour of blood. Simulations of fluid-filled spherical capsules which have red-blood-cell membrane properties also display deformation-induced shear-thinning behaviour at 40 % volume fraction, although the suspension viscosity is significantly lower than blood.

Spinner-flask bioreactors have been used for the production of articular cartilage in vitro. The dynamic environment within bioreactors is known to significantly affect the growth and development of the tissue. The present research focuses on the experimental and numerical characterization of the flow field within a spinner flask operating under conditions used to produce cartilage. Laboratory experiments carried out in a scaled-up model bioreactor employ particle-image velocimetry (PIV) to determine velocity and shear-rate fields in the vicinity of the construct closest to the stir bar, in addition to turbulence properties. Numerical computations calculated using FLUENT, a commercial software package, simulate the flow field in the same model bioreactor under similar operating conditions. In the computations, scaffolds were modeled as both solid and porous media with different permeabilities and flow rates through various faces of the construct nearest the stir bar were examined.

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▪ Abstract  We examine situations in which two droplets of the same liquid may come into apparent contact without coalescing or in which a droplet that normally wets a surface may deform against it without actually wetting it. The focus of this review is on cases driven by hydrodynamic lubrication, the lubricant provided either by surface motion or by evaporation.

Linear-stability theory has been applied to a basic state of thermocapillary convection in a model half-zone to determine values of the Marangoni number above which instability is guaranteed. The basic state must be determined numerically since the half-zone is of finite, O(1) aspect ratio with two-dimensional flow and temperature fields. This, in turn, means that the governing equations for disturbance quantities are nonseparable partial differential equations. The disturbance equations are treated by a staggered-grid discretization scheme. Results are presented for a variety of parameters of interest in the problem, including both terrestrial and microgravity cases; they complement recent calculations of the corresponding energy-stability limits.

Energy stability theory is employed to determine lower bounds on onset times and global stability bounds for initially isothermal fluid layers subjected to impulsive changes in surface temperature. Various combinations of rigid and free boundary conditions and heating or cooling are considered.