Rennes University, France
Title: Marangoni flows, effect of surfactants.
Surface tension gradients induce flows, known as Marangoni flows. They play an enhanced role in systems with a large amount of free interfaces, such as foams, emulsions and thin liquid films. In such systems, the interfaces are deformable, making the
numerical or analytical computations of flows difficult. The presence of surfactants, responsible for the Marangoni stress, still increases the complexity of the problem, which involves interface/bulk exchange and surfactant diffusion both in the bulk and at the interface.
We will present few examples of Marangoni flows, with both an experimental and a scaling law approach.
Polish Academy of Sciences, Poland
Title: Droplet Microfluidics
Droplet microfluidics offers a broad portfolio of techniques for generation and handling of micro-droplets. These allow to rationally design not only simple emulsions but also complex multiple droplets and droplet 'crystals'. Droplets ranging in volume from pico- to micro-liters can also be used in a diverse range of applications in chemistry, biochemistry and microbiology as isolated reactors. The applications of these techniques range from screening of large libraries of droplets containing individually encapsulated molecules or cells, through automated systems for long term parallel screening of reaction and incubation conditions, to passive systems offering execution of complex liquid handling protocols with minimum external control of the process. The talk will review the techniques and potential applications in research and diagnostics.
Universidad Politécnica de Madrid, Spain
Title: Physics and numerical simulations of electrosprays
Electric stresses acting on the surface of a liquid with finite electrical conductivity that is immersed in an electric field may overcome surface tension stresses and break the liquid into electrically charged droplets. The phenomenon finds application in electrosprays, which have the ability to generate nearly monodisperse droplets of controllable size in the micrometer and nanometer ranges. The spray generation process and the dynamics of the spray of charged droplets will be discussed.
La Sapienza University, Italy
Title: Wall bounded compressible turbulence
Turbulence in high-speed boundary layers is a subject of utmost importance in
aerospace applications, bearing consequence on the aerodynamic and thermal design
of aircraft. Similarities and differences between low-speed and high-speed wall
turbulence were highlighted in a number of early studies, with the main conclusion
that genuine compressibility effects (i.e. associated with finite dilatation) are
generally weak, whereas the main role is played by mean density and viscosity
variations. This hypothesis led to the celebrated van Driest transformation, which is
known to work well for adiabatic boundary layers. However, experimental studies of high-speed boundary layers are hampered by considerable technical difficulties, and
in fact the scatter is very large even for basic statistical properties. On the other
hand, direct numerical simulations have not reached yet the level of maturity as their
It is the main purpose of this presentation to present the current status of
knowledge of the subject with the help of recent DNS data for canonical flows,
including boundary layers, channel and pipe flow, at friction Reynolds number up to
Reτ=4000, for the case of adiabatic and cool walls. Fundamentals of accurate and
efficient numerical discretization will be briefly outlined. From a physical standpoint,
the DNS data will be exploited to help answer some fundamental, as yet unsorted
questions : I) does flow compressibility play a genuine role in the boundary layer
dynamics?; II) is there a way to map compressible boundary layer statistics to
incompressible ones?; III) related to the previous item, how to account for
compressiblity and heat transfer effects on the wall friction?; IV) what is the effect of
flow compressibility on the size of the eddies of wall turbulence?; V) what is the
typical wall pressure signature of high-speed boundary layers? Concluding remarks will be given with suggestions for potential avenues of future research.
Imperial College, UK
Title: Gradient-based fluid dynamics: from simulation to control and design
With increasing complexity and scale of numerical simulations of fluid flows, the problems we pursue and questions we ask become commensurably complicated. In the past, numerical simulations have been used to produce high-fidelity output to user-specified input. More recently, the inverse problem is being tackled: given a user-specified objective, we desire control strategies, design modifications or other manipulative measures to achieve this goal with a minimum amount of effort. Questions of this type require gradient or sensitivity information about the flow, which can be gained by formulating adjoint algorithms, equations or variables. We will introduce a general gradient-based framework for the analysis of compressible and incompressible fluid systems based on chained sparse matrix products (and their adjoints) and demonstrate the potential of this approach on two applications: (i) the analysis and control of tonal noise around an airfoil and (ii) the optimization of mixing by a blowing-and-suction strategy. Various extensions of this framework to related application areas will also be discussed.
Aix Marseille University, France
Title: Disgregation of Liquids
Capillarity is the familiar manifestation of the cohesion of Liquids. Since Laplace (1805), we know that intense attractive forces between the molecules bridge the small with the large since they shape liquid/vapor interfaces (meniscii, capillary rise, drops etc…) at macroscopic scales through the concept of surface tension. We will be concerned with situations where liquids `disgregate’, following the neologism of R. Clausius (1862), meaning that they fragment by the action of deformations whose intensity competes with that of cohesion forces. Various examples including explosions, blow-ups, hard and soft impacts, and stretchings applied to liquid jets, sheets and drops will be reviewed. In spite of their diversity, they share a common phenomenology suggesting that the fragments (the final stable droplets) size distribution can be, in general, interpreted from elementary principles.
Z Jane Wang
Cornell University, USA
Title: Insect Flight: From Flight Dynamics to motor Neurons
Why do animals move the way they do? Bacteria, insects, birds, and fish share with us the necessity to move so as to live. While each organism follows its own evolutionary course, it also obeys a set of common laws. At the very least, the movement of animals, like that of planets, is governed by Newton’s law: all things fall. On earth, most things fall in air or water, and their motions are thus subject to the laws of hydrodynamics. Through trial and error, animals have found ways to interact with fluid so they can float, drift, swim, sail, glide, soar, and fly. This elementary struggle to escape the fate of falling shapes the development of motors, sensors, and mind. Perhaps we can deduce parts of their neural computations by understanding what animals must do so as not to fall.
I will discuss our recent work along this line of inquiry in the case of insect flight. Asking how often a fly must sense its orientation in order to balance in air has shed new light on the role of motor neurons and steering muscles responsible for flight stability.