非常に高いレイリー数で渦巻コンベクション
1Department of Physics, University of Oregon, Eugene 97403, USA.
Nature
|April 29, 2000
まとめ
渦巻コンベクション熱伝達は,予測されたRa ((1/2) のスケーリングに従わない. 新しい研究は,レイリー数値の広い範囲にわたって一貫したRa ((0.31)) のスケーリングを示し,既存の理論に挑戦しています.
科学分野:
- 流体力学 流体力学
- 熱力学は熱力学である.
- 熱移転による熱移転
背景:
- 乱流コンベクションは,高いレイリー数 (Ra) の熱グラデントによって引き起こされる.
- 熱伝導特性,特にヌッセルト数 (Nu) を理解することは極めて重要です.
- 理論的なモデルは,非常に高いRa.で,NuスケーリングがRa(1/2) となるアシンプトティックレジームを予測しています.
研究 の 目的:
- レイリー数値の拡張範囲における乱流コンベクションにおける熱輸送を調査する.
- Ra(1/2) のスケーリングを持つアシンプトティックレジームが存在するかどうかを判断する.
- 内部温度変動と速度統計を分析する.
主な方法:
- 低温ヘリウムガスを使って実施された実験.
- レイリー数 (10^6から10^7) の11桁の大きさで測定を行った.
- 熱伝送 (ヌッセルト数) と温度変動の分析.
主要な成果:
- データは一貫して単一の力法則に従っており,Nu は Ra ((β)) に比例する.
- 観測されたスケーリング指数は一貫してβ ≈ 0.31.31です.
- 理論的に予測されたRa ((1/2) 体制への移行の証拠は見つかりませんでした.
結論:
- この研究は,乱流コンベクションにおける予測されたRa ((1/2) アシンプトティックレジムの存在に異議を唱える.
- 約0.31の恒定スケーリング指数は,広大なRa範囲で熱伝送を制御します.
- 渦巻コンベクション熱伝達のモデルを精錬するためにさらなる研究が必要である.
関連する概念動画
Laminar and Turbulent Flow
9.7K
Fluid dynamics is the study of fluids in motion. Velocity vectors are often used to illustrate fluid motion in applications like meteorology. For example, wind—the fluid motion of air in the atmosphere—can be represented by vectors indicating the speed and direction of the wind at any given point on a map. Another method for representing fluid motion is a streamline. A streamline represents the path of a small volume of fluid as it flows. When the flow pattern changes with time, the...
9.7K
Poiseuille's Law and Reynolds Number
8.3K
Any fluid in a horizontal tube can flow due to pressure differences—fluid flows from high to low pressure. The flow rate (Q) is the ratio of pressure difference and resistance through a horizontal tube. The greater the pressure difference, the higher the flow rate. The flow resistance is expressed as:
8.3K
Irrotational Flow
1.3K
Irrotational flow is characterized by fluid motion where particles do not rotate around their axes, resulting in zero vorticity. For a flow to be irrotational, the curl of the velocity field must be zero. This imposes specific conditions on velocity gradients. For instance, to maintain zero rotation about the z-axis, the gradient condition:
1.3K
Steady, Laminar Flow Between Parallel Plates
1.1K
Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
1.1K
Dimensionless Groups in Fluid Mechanics
1.1K
Dimensionless groups in fluid mechanics provide simplified ratios that help analyze fluid behavior without relying on specific units. The Reynolds number (Re), which represents the ratio of inertial to viscous forces, distinguishes between laminar and turbulent flows, making it essential in the design of pipelines and aerodynamic surfaces. The Froude number (Fr), the ratio of inertial to gravitational forces, is particularly useful in predicting wave formation and hydraulic jumps in...
1.1K
Turbulent Flow
927
Turbulent flow is characterized by unpredictable fluctuations in velocity and pressure, which result in a chaotic fluid movement distinct from the orderly patterns of laminar flow. While laminar flow is governed by smooth, parallel layers with minimal mixing, turbulent flow exhibits highly irregular, three-dimensional patterns. This behavior arises due to instabilities in the fluid's velocity profile, and amplifies as the flow velocity increases. Minor disturbances, known as turbulent...
927


