Some Further Aspects of Stable Boundary-Layer Simulation using the EnFlo Stratified-Flow Wind Tunnel

It is demonstrated that the vertical profile of gradient Richardson number, <em>Ri</em>, can be shaped by control of the working-section inlet temperature profile. In previous work in the same facility (Hancock and Hayden, Boundary-Layer Meteorol 168:20-57, 2018; 175:93-112, 2020; 180:5-26, 2021) the inlet temperature profile had been specified but without control of the profile of https://:0/ in the developed-flow region of the working section. In essence, control of <em>Ri</em> is via control of inlet temperature profile provided by the 15 inlet heaters (spread uniformly across the height of the working section), which broadly controls the <em>gradient</em> over the bulk of the boundary layer, and the profile overall <em>level</em> above that of the surface temperature, which controls the surface heat flux and the lower https://:0/1/3 of the boundary layer. In the upper https://:0/2/3 of the boundary layer, the Reynolds stresses are controlled by the <em>gradient</em> in mean temperature, while in the lower https://:0/1/3 they are controlled by the <em>level</em> above the surface temperature. In three examples, https://:0/ is roughly constant at 0.07, 0.10 and 0.13 across the bulk of the layer. The previous observation of (streamwise) horizontally homogenous behaviour in the temperature profiles in the top https://:0/2/3 of the boundary layer but not in the lower https://:0/1/3 is repeated here, except when, tentatively, <em>Ri</em> does not exceed 0.05 over the bulk of the boundary layer. The bulk Richardson number for the 11 cases covers the range 0.01 to 0.17 (there is no overlying inversion). Favourable validation comparisons are made against two sets of local scaling systems and field data over the full depth of the boundary layer, over the range 0.006 &lt; <em>Ri</em> &lt; 0.3, and 0.005 &lt; <em>z/L</em> &lt; 0.30

研究表明，梯度理查森数（gradient Richardson number，<em>Ri</em>）的垂直剖面可通过调控工作段入口温度剖面进行塑造。此前在同一实验装置中的相关研究（Hancock与Hayden，《Boundary-Layer Meteorol》168:20-57, 2018；175:93-112, 2020；180:5-26, 2021）中，虽已设定入口温度剖面，但未对工作段充分发展流区域内的https://:0/剖面进行调控。本质而言，对<em>Ri</em>的调控可通过15个沿工作段高度均匀分布的入口加热器所提供的入口温度剖面实现：该调控方式可大致控制边界层大部分区域的平均温度梯度，以及高于表面温度的剖面整体基准值；其中基准值可控制表面热通量与边界层下部的https://:0/1/3区域。在边界层上部的https://:0/2/3区域内，雷诺应力由平均温度梯度调控；而在下部的https://:0/1/3区域内，雷诺应力则由高于表面温度的基准值决定。在三个示例工况中，边界层大部分区域的https://:0/大致稳定在0.07、0.10与0.13。本次研究再次重现了此前的观测结果：边界层上部https://:0/2/3区域内的温度剖面呈现顺流方向水平均一性特征，而下部https://:0/1/3区域则无此特征；仅当边界层大部分区域的<em>Ri</em>未超过0.05时（该结论为初步推断），此规律例外。本次11个工况的整体理查森数（bulk Richardson number）覆盖0.01至0.17的范围（无上方逆温层）。针对0.006 < <em>Ri</em> < 0.3、0.005 < <em>z/L</em> < 0.30的参数范围，研究分别通过两套局地标度系统与全边界层深度的野外观测数据开展验证，对比结果良好。