Transient growth and resolvent analyses are routinely used to assess non-asymptotic properties of fluid flows. In particular, resolvent analysis can be interpreted as a special case of viewing flow dynamics as an open system in which free-stream turbulence, surface roughness, and other irregularities provide sources of input forcing. We offer a comprehensive summary of the tools that can be employed to probe the dynamics of fluctuations around a laminar or turbulent base flow in the presence of such stochastic or deterministic input forcing and describe how input-output techniques enhance resolvent analysis. Specifically, physical insights that may remain hidden in the resolvent analysis are gained by detailed examination of input-output responses between spatially-localized body forces and selected linear combinations of state variables. This differentiating feature plays a key role in quantifying the importance of different mechanisms for bypass transition in wall-bounded shear flows and in explaining how turbulent jets generate noise. We highlight the utility of a stochastic framework, with white or colored inputs, in addressing a variety of open challenges including transition in complex fluids, flow control, and physics-aware data-driven turbulence modeling. Applications with time- or spatially-periodic base flows are discussed and future research directions are outlined.

中文翻译：

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从旁路过渡到流量控制和数据驱动的湍流建模：输入-输出观点

瞬态增长和溶剂分析通常用于评估流体流动的非渐近特性。特别是，解析度分析可以解释为将流动动力学视为开放系统的一种特殊情况，其中自由流湍流、表面粗糙度和其他不规则性提供输入强迫源。我们提供了可用于探测在存在此类随机或确定性输入强迫的情况下围绕层流或湍流基流波动动态的工具的全面总结，并描述了输入输出技术如何增强解析分析。具体来说，通过详细检查空间局部体力和选定的状态变量线性组合之间的输入-输出响应，可以获得可能隐藏在解析解分析中的物理见解。这种差异化特征在量化壁面剪切流中旁路过渡的不同机制的重要性以及解释湍流射流如何产生噪声方面起着关键作用。我们强调了具有白色或彩色输入的随机框架在解决各种开放挑战方面的效用，包括复杂流体的过渡、流动控制和物理感知数据驱动的湍流建模。讨论了具有时间或空间周期性基流的应用，并概述了未来的研究方向。解决各种开放挑战，包括复杂流体的过渡、流动控制和物理感知数据驱动的湍流建模。讨论了具有时间或空间周期性基流的应用，并概述了未来的研究方向。解决各种开放挑战，包括复杂流体的过渡、流动控制和物理感知数据驱动的湍流建模。讨论了具有时间或空间周期性基流的应用，并概述了未来的研究方向。