Lagrangian and Eulerian analysis of superstructures in wall-bounded turbulence based on large-scale, time-resolved and volumetric measurements using Shake-The-Box and FlowFit

在这个项目中，我们建议为新的实验流量测量技术的应用提供资金，旨在详细研究高雷诺数湍流边界层(TBL)和管流中的超结构。使用DLR自己的Shake-the-Box(STB)技术进行的三维时间分辨流动测量是基于迄今为止无与伦比的粒子密度的拉格朗日粒子跟踪，并在大小测量体积上提供高空间分辨率的速度场和加速场。测量体的高分辨率允许同时分辨多尺度湍流中的大范围尺度，特别是它允许捕捉扩展的超结构并研究它们与小尺度的相互作用和影响。单个测量点来自单个粒子的轨迹，保证了速度场和加速场的高精度。此外，DLR发展的非线性数据同化方法Flowfit将被应用于测量体积中粒子轨迹位置的任意分布的速度和加速度矢量，以便通过在整个测量体积内实施连续性和来自Navier-Stokes的动量方程来实现三维速度矢量和压力场的连续表示。在SPP 1881项目的第一阶段，STB测量技术已经成功地应用于高雷诺数下的大规模湍流边界层实验，使用HFSB和脉冲LED照明。在慕尼黑的AWM中，在一个长2.9米、宽80厘米、高25厘米的体积内同时跟踪了多达630,000个颗粒，该体积沿湍流边界层流动，经历了从零到正压梯度的变化，随后发生了流动分离。在这项运动中，上部结构的测量速度达到了21m/s。在第二个项目阶段，将使用经过验证的STB方法来研究Cottbus公司CoLaTube高雷诺数湍流管流中的上部结构。为了进一步研究超结构影响下壁面附近的速度波动，将沿着几厘米长的壁面正常激光束进行时间分辨STB测量。得到的数据集在时间和空间分辨率上都是唯一的，并且在空间和空间范围上都超出了数值模拟的时空范围。

In this project, we propose funding for the application of novel experimental flow measurement techniques aiming at the detailed investigation of superstructures in high Reynolds number turbulent boundary layers (TBL) and pipe flows. The three-dimensional time-resolved flow measurements with the DLR own Shake-The-Box (STB) technique are based on Lagrangian particle tracking at so far unrivaled particle densities and provide velocity and acceleration fields at a high spatial resolution over large and small measurement volumes. The high resolution in a measurement volume allows to simultaneously resolving a broad range of scales in the multi-scale turbulent flows, in particular, it allows capturing extended superstructures and studying their interaction with and influence on smaller scales. Single measurement points are derived from individual particle trajectories, guaranteeing a high accuracy of the velocity and acceleration fields. Furthermore, the non-linear data assimilation method FlowFit, as well developed at DLR, will be applied to the arbitrary distributed velocity and acceleration vectors at the particle track positions in the measurement volume in order to achieve a continuous representation of the 3D velocity vector and pressure fields by enforcing continuity and the momentum equation from Navier-Stokes in the whole measurement volume.In the first phase of the project within the SPP 1881 the STB measurement technique has been applied successfully to a large scale turbulent boundary layer experiment at high Reynolds numbers by using HFSB and pulsed LED illumination. In the AWM in Munich up to 630,000 particles have been tracked simultaneously within a 2.9 m long, 80 cm wide and 25 cm high volume which was placed along a turbulent boundary layer flow undergoing a change from zero to positive pressure gradients with subsequent flow separation. In this campaign superstructures have been measured up to flow velocities of 21 m/s.In the second project phase the well-proven STB method shall be applied for the investigation of superstructures in high Reynolds number turbulent pipe flows of the CoLaPipe in Cottbus. In order to additionally investigate the velocity fluctuations near the wall under the influence of superstructures time-resolved STB measurements will be undertaken along a several centimeter long wall-normal laser beam with approx. 10 x 3 mm² cross section at ~20 – 80 kHz in both turbulent boundary layer and pipe flows.The obtained data sets are unique in their temporal and spatial resolution, in their spatial extent, and go beyond the capabilities of DNS in their spatial and temporal extent.