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雷诺平均纳维-斯托克斯 (RANS) 方程

1895
  • Osborne Reynolds
19th-century laboratory with Reynolds-Averaged Navier-Stokes Equations for fluid mechanics analysis.

(图片仅供参考)

The Reynolds-Averaged Navier-Stokes (RANS) equations are time-averaged equations of motion for turbulent fluid flow. This approach, called Reynolds decomposition, separates flow variables into a mean and a fluctuating component. The averaging process introduces an additional term, the Reynolds 压力 tensor, which represents the effect of turbulence and must be modeled to achieve closure, making simulations computationally tractable.

The core idea behind RANS is Reynolds decomposition, where an instantaneous quantity is split into its time-averaged and fluctuating parts. For velocity, this is [latex]u_i(x,t) = \bar{u}_i(x) + u’_i(x,t)[/latex]. When this is substituted into the Navier-Stokes equations and the equations are time-averaged, the non-linear convective term generates a new term, [latex] -\rho \overline{u’_i u’_j} [/latex], known as the Reynolds stress tensor. This tensor represents the net transfer of momentum due to turbulent fluctuations.

The appearance of this unknown tensor leads to the ‘closure problem’ of turbulence: there are more unknowns than equations. To solve the system, the Reynolds stresses must be related to the mean flow quantities through a turbulence model. The most common approach is the Boussinesq hypothesis, which assumes the Reynolds stresses are proportional to the mean strain rate, introducing an ‘eddy viscosity’ or ‘turbulent viscosity’. This is analogous to how molecular 粘度 relates stress to strain rate in laminar flow. Turbulence models, such as the popular k-ε (k-epsilon) and k-ω (k-omega) models, are sets of additional transport equations used to compute this eddy viscosity throughout the flow field. For example, the k-ε model solves for the turbulent kinetic energy (k) and its rate of dissipation (ε). RANS provides a good balance of accuracy and computational cost for many engineering applications, as it avoids the prohibitive expense of resolving all turbulent eddies directly.

UNESCO Nomenclature: 2205
– Fluid Mechanics

类型

抽象系统

中断

Foundational

用法

广泛使用

前体

  • 纳维-斯托克斯方程
  • Osborne Reynolds’ experiments on flow transition from laminar to turbulent
  • 统计力学和时间平均概念
  • Joseph Boussinesq’s eddy viscosity hypothesis

应用程序

  • 商用飞机机翼和机身的设计
  • 喷气发动机和涡轮机等涡轮机械的分析
  • 船体流体动力学设计
  • 内燃机的流动建模
  • 土木工程应用,例如建筑物的风荷载
  • 用于分析运动员和装备的空气动力学的运动科学

专利:

NA

潜在创新理念

  • 机器学习增强型 RAS 模型,可从高保真 DNS 数据中学习
  • 基于 RAS 的飞机起落架降噪优化
  • real-time rans simulations for controlling wind farm turbine yaw angles
  • 使用基于 Rans 的湍流预测器对血液凝固和血栓形成进行建模
  • simulating atmospheric boundary layer interactions with urban heat islands
  • 优化工业反应器中的化学混合过程
  • 预测洪水期间河流系统的泥沙输送
  • 为办公空间开发个性化通风系统
Related to: rans, turbulence modeling, reynolds stress, closure problem, k-epsilon, k-omega, cfd, eddy viscosity.

历史背景

雷诺平均纳维-斯托克斯 (RANS) 方程

1889
1890
1890
1895
1895
1896
1900
1888
1889
1890
1890
1895
1895
1899
1900

(如果日期未知或不相关,例如“流体力学”,则提供其显著出现的近似估计)

第十年 周年纪念日

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