L. Danaila教授 (フランス、Rouen大学) による、流体力学に関する講演を開催しますので、博士前期学生、博士後期学生の皆様は奮ってご参加ください。

 

日時： 2017年4月14日（金）16：00－17：00
場所： 2号館　B棟1階　0212講義室                   

 

なお，本講演は博士前期･博士後期「特別演習」認定講義となりますので，出席の上，必要な条件を満たした場合は，以下の科目の認定要件に加算されます。

・材料・エネルギー特別演習１・２
・情報・社会特別演習１・２
・材料・エネルギー先進特別演習１・２
・情報・社会先進特別演習１・２

 

主催： 日本流体力学会中部支部
担当教員： 後藤俊幸教授

URL：http://comphys.web.nitech.ac.jp/

概要：Turbulent mixing is ubiquitous in both nature and industrial applications. Most of them involve different fluids, therefore with variable physical properties (density and/or viscosity). The focus here is on variable-viscosity flows and mixing in density-matched fluids. The issue is whether or not these flows may be self-similar, or self-preserving. The importance of the question stands on the predictability of these flows; self-similar dynamical systems are much easier tractable from an analytical viewpoint. Self-similarity analysis, as first introduced by Townsend, is applied to the relevant transport equations of the velocity field (mean momentum, one-point energy budget equation as well as scale-by-scale energy transport equations- the latter represent the transport of energy at each scale and each point of the flow). Extensions of these equations for the transport of the scalar field are discussed, with particular focus on their mathematical analogy. It is str  essed that neither local isotropy nor high Reynolds numbers are necessary conditions for the similarity to be valid. Scale-by-scale energy budget equations are developed for flows in which the viscosity varies as a result of heterogeneous mixture or temperature variations. Additional terms are highlighted, accounting for the viscosity gradients, or fluctuations. These terms are present at both small and large scales, thus rectifying the common belief that viscosity is a small-scale quantity. This will be illustrated with results obtained either experimentally (in a jet) or numerically (in a temporally evolving mixing layer). Scale-by-scale energy budget equations are written for anisotropic, decaying flows, evolving in a more viscous host fluid. It is further shown that the condition of self-preservation is not necessarily satisfied in variable-viscosity jets. As far as round jet is concerned, the jet momentum conservation, as well as the constancy of the Reynolds number alo  ng the axis of the jet, cannot be satisfied simultaneously. This points to the necessity of considering less stringent conditions (with respect to classical, single-fluid jets) when analytically tackling these flows and reinforces the idea that viscosity variations must be accounted for when modelling these flows.