遭遇自由流湍流的风力机尾流中的耗散尺度
Dissipation scaling in wind turbine wakes exposed to free-stream turbulence
- Imperial College London（帝国理工学院）
- Nantes Université, École Centrale Nantes（南特大学，中央理工学院南特分校）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本实验探究风力机尾流在不同强度自由流湍流下的湍动能耗散尺度，发现低/中等强度湍流下叶尖区域耗散呈特定尺度规律，高强度湍流下大尺度间歇性被抑制。
AI中文摘要：
本研究通过实验探究了直径D=0.58m的风力机在遭遇多种不同类型的高雷诺数自由流湍流（FST）时，湍动能（TKE）耗散的特性。对于低强度和中等强度的FST，在外尾流区域会形成一个归一化耗散率C_ε升高的环形区域，该区域同时对应着小尺度（ℓ≤λ，λ为泰勒微尺度）和大尺度（ℓ≥D）下湍流间歇性增强的环带。在叶尖区域，C_ε遵循√Re_D/Re_λ的尺度规律，其中Re_D为全局雷诺数，Re_λ为基于泰勒微尺度λ的局地湍流雷诺数——该尺度表明耗散与能量级串惯性范围内的湍动能跨尺度通量处于非平衡状态。结合观测到的间歇性，这种非平衡状态可解释为：在低强度FST驱动下，持续的叶尖涡和叶尖剪切层动力学产生的大尺度间歇性事件（即低波数扰动或“冲击”）需要有限时间才能级串至耗散尺度，从而在跨尺度能量通量与耗散之间引入不平衡。相比之下，在尾流中心线处，C_ε沿流向距离近似保持恒定，这既可能反映经典的柯尔莫哥洛夫型平衡湍流，也可能反映非平衡湍流的平衡状态，此时间歇性仅局限于小尺度。在高强度FST下，大尺度间歇性被抑制，这与叶尖涡结构的侵蚀一致；对于此类案例，由于存在两条来源不同、强度相近的相邻湍流流束，无法用单一湍流雷诺数确定C_ε的可比尺度。
英文摘要：
The nature of the dissipation of turbulent kinetic energy (TKE) is investigated experimentally in the wake of a diameter $D=0.58$m wind turbine exposed to several ``flavours'' of high-Reynolds-number free-stream turbulence (FST). For low- and moderate-intensity FST, an annular region of elevated normalised dissipation, $C_{\varepsilon}$, develops in the outer wake, coinciding with a ring of enhanced turbulence intermittency at both small ($\ell \leq λ$) and large ($\ell \geq D$) scales, where $λ$ is the Taylor microscale. In the blade-tip region, $C_{\varepsilon}$ scales with $\sqrt{Re_D}/Re_λ$, where $Re_D$ is a global Reynolds number and $Re_λ$ a local turbulent Reynolds number based on $λ$-a scaling indicative of dissipation being out of equilibrium with the inter-scale flux of TKE in the inertial range of the energy cascade. This non-equilibrium regime is interpreted in light of the observed intermittency : large-scale intermittent events (i.e., low-wavenumber perturbations/``kicks''), driven by persistent tip-vortex and tip-shear-layer dynamics under low-intensity FST, require a finite time to cascade down to the dissipative scales, thereby introducing an imbalance between the inter-scale energy flux and dissipation. At the wake centreline, by contrast, $C_{\varepsilon}$ remains approximately constant with streamwise distance, reflecting either classical Kolmogorov-type equilibrium turbulence or balanced non-equilibrium turbulence, with intermittency confined to the small scales. Under high-intensity FST, large-scale intermittency is suppressed, consistent with the erosion of tip-vortex structures, and no comparable scaling for $C_{\varepsilon}$ could be identified using a single turbulent Reynolds number for these cases, where two similarly intense streams of turbulence, but of different origins, are adjacent to one another.
