Abstract The vibration of rods is of prime importance to estimate their wearing due to the frictions with grids’ elements. To predict this wearing, the pressure fluctuations exerted on the rods need to be identified and quantified. Pressure fluctuations are explored using an instrumented rod centred within a 5 × 5 rods bundle. The profiles of mean velocity and velocity fluctuations are explored around the instrumented rod using LDV. Two configurations of spacer-grids are used: with and without mixing vanes respectively noted WMV and NMV. The position of the measurement point is rotated over 360° and its distance from the grids is varied from 0.5Dh to 20Dh. The results are detailed for the Reynolds number 66000. The results show the non-homogeneity of the azimuthal distribution of the pressure fluctuations in the near wake of the spacer-grids for both configurations. The return to a homogeneous azimuthal distribution of the pressure fluctuations is faster without mixing vanes than with mixing vanes. The intensities of the pressure fluctuations are (in average) higher for WMV than for NMV by 13% and 136% at distances 0.5Dh and 20Dh from the grids respectively. The correlation functions and energy spectra highlight significant differences in the spatial and temporal structure of the pressure fluctuations for the configurations with and without mixing vanes. For both configurations, pressure fluctuations spectra reveal a frequency peak in the near wake of the grids. These peaks are around f D h / V flow ≈ 0.8 (69 Hz). Maxima are found at f ∗ = 0.78 (66.8 Hz) and f ∗ = 0.87 (74.6 Hz) respectively for WMV and NMV configurations. This frequency peaks persist farther from the grid for NMW than for WMV. The integral scale of pressure fluctuations highlight to different behaviour. The pressure integral length scale stays small compared to Dh (ranging from 0.13Dh to 0.2Dh) for the NMV configuration whilst it increases with the distance from the grid for the WMV case. This is coherent with the persistence of frequency peaks for the NMV configurations. The pressure integral length scale is found to be 2–9 times larger for WMV than for NMV with the increase of the distance from the grid between 0.5Dh and 20Dh. A significant anti-correlated domain appears for NMW and not for WMV. In addition, LDV results show oscillations of the velocity profiles and a damping with the distance from the grids. Between 2Dh and 15Dh, the dimensionless ratio of “pressure fluctuations to velocity fluctuations” 〈 P rms ' 〉 θ / 1 2 ρ 〈 v rms ' 2 〉 P s q is found to increase by about 70% and 100% respectively for the configurations NMV and WMV. This increase further reveals the complexity of the turbulent flow in the wake of spacer-grids.

中文翻译：

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使用带和不带混合叶片的网格在 5 × 5 棒束中测量非定常压力和速度

摘要 由于与网格元件的摩擦，杆的振动对于估计其磨损至关重要。为了预测这种磨损，需要识别和量化施加在杆上的压力波动。使用以 5 × 5 棒束为中心的仪表棒探索压力波动。使用 LDV 在仪器杆周围探索平均速度和速度波动的轮廓。使用了两种配置的间隔网格：带有和不带有混合叶片，分别标注为 WMV 和 NMV。测量点的位置旋转了 360°，它与网格的距离从 0.5Dh 到 20Dh 变化。雷诺数 66000 的详细结果。结果显示了两种配置的间隔网格附近尾迹中压力波动的方位角分布的非均匀性。没有混合叶片比使用混合叶片更快地恢复到压力波动的均匀方位角分布。在距网格 0.5Dh 和 20Dh 的距离处，WMV 的压力波动强度（平均）比 NMV 高 13% 和 136%。相关函数和能谱突出了带有和不带有混合叶片的配置的压力波动的空间和时间结构的显着差异。对于这两种配置，压力波动谱在网格的尾流附近显示频率峰值。这些峰值在 f D h / V flow ≈ 0.8 (69 Hz) 附近。最大值出现在 f ∗ = 0.78 (66. 8 Hz) 和 f ∗ = 0.87 (74.6 Hz) 分别用于 WMV 和 NMV 配置。与 WMV 相比，NMW 的此频率峰值离电网更远。压力波动的积分尺度突出显示不同的行为。与 NMV 配置的 Dh（范围从 0.13Dh 到 0.2Dh）相比，压力积分长度尺度保持较小，而对于 WMV 情况，它随着与网格的距离而增加。这与 NMV 配置的频率峰值的持续性是一致的。发现随着距网格的距离在 0.5Dh 和 20Dh 之间增加，WMV 的压力积分长度尺度比 NMV 大 2-9 倍。一个重要的反相关域出现在 NMW 而不是 WMV。此外，LDV 结果显示速度剖面的振荡和与网格距离的阻尼。在 2Dh 和 15Dh 之间，发现 NMV 配置的“压力波动与速度波动”的无量纲比 〈 P rms ' 〉 θ / 1 2 ρ 〈 v rms ' 2 〉 P sq 分别增加了约 70% 和 100%和 WMV。这种增加进一步揭示了间隔网格后湍流的复杂性。