by 神田研究室

東京工業大学 融合理工学系 神田研究室 から特別講演のお知らせです！

「乱流摩擦抵抗におけるスペクトルリンク」

by Dr. Pinaki Chakraborty (沖縄科学技術研究所)

日時：2017年10月20日（金） 17:00－

場所：東京工業大学 石川台4号館 地下一階 B04

※英語での講演です。

乱流スペクトルについての興味深いお話を聞くことができます。

興味のある方はぜひいらしてください。

Abstract:

Two aspects of turbulent flows have been the subject of extensive, but
separate, research efforts: the macroscopic properties and the turbulent
spectrum. The macroscopic properties include the frictional drag experienced
by a flow past a wall. The turbulent spectrum represents the statistics
of fluctuations in the flow. The link, if any, between the macroscopic
properties and the turbulent spectrum has remained missing. My talk concerns
this missing “spectral link.” First, I will outline a spectral theory of
the frictional drag that expresses the frictional drag as a functional
of the turbulent spectrum. For three-dimensional flows in smooth and rough
pipes, I will obtain an analytical version of the arch-famous Nikuradse’s
diagram that is in minute qualitative agreement with the distinctive features
in the diagram that have remained elusive to any theoretical elucidation.
I will show that the exponents of the empirical scalings in the diagram
are set by the attendant spectral exponent for “energy cascade” spectrum.
Thereafter, I will consider quasi-two-dimensional turbulent flows—the realm
of large-scale atmospheric and oceanic flows. I will describe unprecedented
experimental measurements of frictional drag in turbulent soap-film flows
over smooth walls, with two disparate types of turbulent spectra: the “enstrophy
cascade,” and the “inverse energy cascade.” I will show that the scaling
of the frictional drag is set by the spectral exponent as per the predictions
of the spectral theory of frictional drag. Last, I will describe preliminary
results from flows where the spectral exponent is non-uniform in the wall-normal
direction.

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