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  • [ September 21, 2018]

    Flame Folding and Wrinkling Factor for 2D and 3D Hydrogen-Air Flames

    | An experimental study and theoretical analysis of laminar flame propagation in spherical 3D- and planar 2D-geometries for hydrogen-air mixtures was carried out in order to investigate an effect of flame instability, a flame structure and a mechanism of initial quasi-laminar flame acceleration prior turbulent flame acceleration and DDT. The theory of laminar flames and theoretical analysis based on solution of Sivashinsky-Michelson equation was performed to explain the experimental results. It was theoretically found, that the burning velocity increased by the factor of 1.2-1.6 due to the flame instability. This value was found to be exactly proportional to the flame area amplification and well confirmed by current experimental data in 2D- and 3D-geometries. Such a flame wrinkling leads to primary flame acceleration remaining the flame of laminar structure in general.?
  • [ September 20, 2018]

    Extrapolating turbulence to higher Reynolds numbers

    | In many practical applications, the Reynolds number Re is much greater than the largest Re that can be achieved in direct numerical simulations and wind-tunnel experiments. Hence, to apply the turbulence-related results obtained in a wind tunnels or with computers, extrapolation to higher Re is needed. For the part of the flow very close to the wall such extrapolation is usually based on the classical universality hypothesis that states that near the wall the turbulent flow parameters, expressed in so-called wall units, are independent of Re. However, in recent years it was established that the large-scale structures residing further away from the wall affect the near-wall turbulence. Since these structures, if expressed in wall units, are not Re-independent, the classical universality hypothesis is not correct. Moreover, recent data indicate that as Re increases the outer large-scale structures become stronger. An outline will be given of the new technique for extrapolating statistical characteristics of near-wall turbulence from medium to higher Re, based on the recently developed quasi-steady quasi-homogeneous (QSQH) theory. The QSQH theory is an alternative to the classical universality hypothesis. The QSQH theory provided relationships between many turbulence parameters previously thought to be unrelated, including for example those entering the well-known empirical formula for the modulation of near-wall turbulence by outer structures, and threw a new light on the Re-dependence of the logarithmic law constants. An overview of the theory will be followed by an explanation of the extrapolation method and examples of its application. The lecture will be concluded by a description of a sensor probe designed for applying the extrapolating technique in experiments.
  • [ July 07, 2018]

    Nanofluidics: A New Arena for Materials Science

    | A significant growth of research in nanofluidics is achieved over the past decade, but the field is still facing considerable challenges toward the transition from the current physics-centered stage to the next application-oriented stage. To conquer these challenges, we established a technology called “nano-in-nano integration”, which allows the integration of a variety of functional (eg., fluidic, electrical, optical, thermal, magnetic, chemical and biological) components in tiny nanofluidic channels. The nano-in-nano integration technology opens up a new arena to exploit chemistry, biology, and materials science at femtoliter, attoliter, single-nanoparticle, and single-molecule scales through nanofluidics, as demonstrated by us in our recent works which will be presented in this talk.
  • [ July 03, 2018]

    Mechano-adaptable Materials for Flexible and Conformal Electronics

    | Smart wearable sensors not only enrich daily lives by providing enhanced smart functions, but also provide health information by monitoring body conditions. For example, patchable sensors have the potential to better interface with human skin, thus improving the sensitivity of detection of health indicators. However, the crucial aspects toward the advancement of such sensors include the development of novel mechanically durable materials, flexible and stretchable substrates, deformable electrodes and circuits, bio-stable and bio-compatible, and so on. In this talk, I will present our latest progress fabricating conformal sensors based on the rational design of structural materials, individual devices development, and integration.
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