Turbulence transport in a density stratified fluid generated by multiple scalars: mechanism of differential diffusion and quantitative evaluation

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03875
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 19010:Fluid engineering-related
• Research Institution: Kyoto University
• Principal Investigator: Okino Shinya 京都大学, 工学研究科, 講師 (30711808)
• Co-Investigator(Kenkyū-buntansha): 花崎 秀史 京都大学, 工学研究科, 教授 (60189579)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 熱塩成層流体 / 減衰乱流 / 高シュミット数 / 二重拡散対流 / 直接数値計算 / レーザー誘起蛍光法 / ソルトフィンガー / 乱流拡散係数

Outline of Final Research Achievements

Direct numerical simulations of decaying turbulence in thermohaline stratified fluids are performed to investigate how instabilities occurring at small scales affect the decay of turbulence. When either the temperature or salt stratification is unstable, potential energy is produced near the diffusive scale of temperature. When the salt stratification is unstable and the flow is subject to the fingering instability, the flow develops again after the initial perturbation decays, forming a vertically elongated density profile (salt fingers). On the other hand, when the temperature stratification is unstable and the flow is subject to the diffusive instability, the potential energy increases significantly in a short time. However, the buoyancy ratio dependence of the decay of the kinetic energy is not very significant, except in the case with strong instability.

Free Research Field

流体物理学

Academic Significance and Societal Importance of the Research Achievements

表層混合層を除く海洋は、温度と塩分によって形成される熱塩成層流体であり、そこでは、温度と塩分の分布による海水の密度差のために、千年スケールの長い時間をかけて地球を巡る流れ（熱塩循環）が駆動されている。熱塩循環は地球規模の極めて大きな熱量や炭素の輸送を担うため、地球温暖化などの気候変動とも密接に関わっており、その予測は重要である。本研究で得られた、熱塩成層流体中の乱流拡散に関する知見は、全球気候モデルの高精度化に寄与するものである。