Simultaneous temperature and velocity Lagrangian measurements in turbulent thermal convection
Simultaneous temperature and velocity Lagrangian measurements in turbulent thermal convection
复制标题
湍流热对流中的同步温度和速度拉格朗日测量
DOI：
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发表时间：
2015
影响因子：
3.7
通讯作者：
F. Chillà
中科院分区：
文献类型：
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作者：
O. Liot;F. Seychelles;Francesco Zonta;Sergio Chibbaro;Thibaut Coudarchet;Y. Gasteuil;J. Pinton;J. Salort;F. Chillà
我们报告联合拉格朗日速度和温度测量湍流热对流。使用中性浮力仪器粒子的改进版本（扩展自主性）进行测量（Shew等人，Rev. Sci.仪器：Vol.78，2007，065105），其由Gasteuil等人（Phys. Rev. Lett.，vol.99，2007，234302）在平行六面体Rayleigh-Bénard池中进行实验。温度信号从射频发射器获得。同时，我们确定一个粒子的位置和速度与一个摄像头，赠款拉格朗日热通量。由于本粒子的扩展自治性，我们获得了收敛良好的温度和速度统计，以及速度和热通量的伪欧拉映射。目前的实验结果也进行了比较，通过相应的运动的直接数值模拟和拉格朗日跟踪的无质量示踪剂所获得的结果。实验和数值计算结果的比较表明了我们的实验测量的准确性和可靠性，也指出了粒子的有限尺寸效应。最后，拉格朗日速度和温度频谱的分析显示和讨论。特别是，我们观察到，温度谱表现出异常的频率标度，可能代表无处不在的被动和主动标量行为的温度。
We report joint Lagrangian velocity and temperature measurements in turbulent thermal convection. Measurements are performed using an improved version (extended autonomy) of the neutrally buoyant instrumented particle (Shew et al., Rev. Sci. Instrum., vol. 78, 2007, 065105) that was used by Gasteuil et al. (Phys. Rev. Lett., vol. 99, 2007, 234302) to performed experiments in a parallelepipedic Rayleigh–Bénard cell. The temperature signal is obtained from a radiofrequency transmitter. Simultaneously, we determine a particle’s position and velocity with one camera, which grants access to the Lagrangian heat flux. Due to the extended autonomy of the present particle, we obtain well-converged temperature and velocity statistics, as well as pseudo-Eulerian maps of velocity and heat flux. Present experimental results have also been compared with the results obtained by a corresponding campaign of direct numerical simulations and Lagrangian tracking of massless tracers. The comparison between experimental and numerical results shows the accuracy and reliability of our experimental measurements and points also out the finite-size effects of the particle. Finally, the analysis of Lagrangian velocity and temperature frequency spectra is shown and discussed. In particular, we observe that temperature spectra exhibit an anomalous $f^{-2.5}$ frequency scaling, likely representing the ubiquitous passive and active scalar behaviour of temperature.