We analyse the metrological aspect related to systems devoted to the simultaneous measurements of (one point) velocity and scalar concentration statistics. We consider systems based on the coupling of an anemometer (laser Doppler or hot wire) with a flame ionization detector. In particular, we focus on the estimate of the cross-correlation velocity-concentration. Key aspects in the reliability of such measurements are related to the identification of an optimal distance between the two probes, the time lag with which the velocity and concentration signals are acquired, and, eventually, the influence of seeding particles (when using a laser Doppler anemometer) on the concentration measurements. We investigate these aspects by performing wind-tunnel experiments on the scalar dispersion downwind a ground-level source in a turbulent boundary layer. This analysis allowed us to identify a time delay and a convenient distance between the signals provided by the anemometer and the concentration detector. Results also show that the seeding used for the laser Doppler anemometer measurements modifies the cut-off frequency in the concentration spectra and induces a slightly larger uncertainty on the statistics of scalar field. The results show the reliability of both systems in estimating (horizontal and vertical) turbulent mass fluxes.

中文翻译：

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风洞实验中湍流中速度和浓度的高频同时测量

我们分析了与致力于同时测量（一点）速度和标量浓度统计数据的系统相关的计量方面。我们考虑基于风速计（激光多普勒或热线）与火焰电离检测器耦合的系统。特别是，我们专注于互相关速度浓度的估计。此类测量可靠性的关键方面与确定两个探头之间的最佳距离、获取速度和浓度信号的时滞以及最终粒子的影响有关（当使用激光多普勒风速计）上的浓度测量。我们通过对湍流边界层中地面源下风向的标量色散进行风洞实验来研究这些方面。这种分析使我们能够确定风速计和浓度检测器提供的信号之间的时间延迟和方便的距离。结果还表明，用于激光多普勒风速计测量的播种修改了浓度谱中的截止频率，并导致标量场统计数据的不确定性稍大。结果表明两个系统在估计（水平和垂直）湍流质量通量方面的可靠性。结果还表明，用于激光多普勒风速计测量的播种修改了浓度谱中的截止频率，并导致标量场统计数据的不确定性稍大。结果显示了两个系统在估计（水平和垂直）湍流质量通量方面的可靠性。结果还表明，用于激光多普勒风速计测量的播种修改了浓度谱中的截止频率，并导致标量场统计数据的不确定性稍大。结果表明两个系统在估计（水平和垂直）湍流质量通量方面的可靠性。