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，我们提出了新的实验流量测量技术的应用，旨在详细调查的上层结构在高雷诺数湍流边界层（TBL）和管流的资金。使用德国航天中心自己的Shake-The-Box（STB）技术进行的三维时间分辨流量测量是基于拉格朗日粒子跟踪，其粒子密度迄今为止无与伦比，并在大小测量体积上以高空间分辨率提供速度和加速度场。测量体积中的高分辨率允许同时解析多尺度湍流中的宽范围尺度，特别是，它允许捕获扩展的超结构并研究它们与较小尺度的相互作用和对较小尺度的影响。单个测量点来自单个粒子的轨迹，保证了速度和加速度场的高精度。此外，德国航天中心开发的非线性数据同化方法FlowFit，将应用于测量体积中粒子轨迹位置处的任意分布的速度和加速度矢量，以便通过实施连续性和Navier动量方程来实现3D速度矢量和压力场的连续表示。在SPP 1881项目的第一阶段，STB测量技术已成功应用于高雷诺数下的大尺度湍流边界层实验，实验采用高频SB和脉冲LED照明。在慕尼黑的AWM中，在2.9 m长、80 cm宽和25 cm高的体积内同时跟踪了多达630，000个颗粒，该体积沿着湍流边界层流动，该湍流边界层流动经历从零到正压梯度的变化，随后发生流动分离。在本次活动中，上部结构的流速已达到21 m/s。在第二个项目阶段，应采用经过验证的STB方法，对科特布斯CoLaPipe的高雷诺数湍流管流中的上部结构进行研究。为了进一步研究上部结构影响下壁面附近的速度波动，将沿沿着几厘米长的壁面法向激光束进行时间分辨STB测量，激光束的长度约为1.5厘米。在湍流边界层和管流中，在~20 - 80 kHz下的10 x 3 mm²横截面。所获得的数据集在时间和空间分辨率以及空间范围方面都是独特的，并且在空间和时间范围方面超出了DNS的能力。

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.