Experiments on very large structures in fully developed turbulent pipe flow

本文研究了高雷诺数、低马赫数条件下的圆管湍流流动。近几年来，人们对大尺度湍流相干结构的观测和理解越来越感兴趣，这些结构通常被称为大尺度和超大尺度运动（LSM和VLSM）。然而，对其性质的确切定义和对其演变的生动理解仍然不完整。因此，本研究将致力于澄清LSM和VLSM的性质和起源，并以定量的方式描述和识别它们。为此，将进行实验和数值计算（与SPP内可能的合作伙伴一起），并尽可能匹配。在科特布斯大型管道试验设备上的试验（CoLa-管道），该管道已成功沿着第一阶段使用，将在体积雷诺数为6 × 10 E4 ≤ Re B ≤ 1 × 10 E6时进行（基于管道直径D和体积速度Ub）和马赫数Ma < 0.23，使用小型热线风速仪（HWA）测量湍流特性，高速粒子图像测速（PIV）和摇动盒子（STB）粒子跟踪技术（与DLR，A.这一建议旨在实现两个突出目标。这两个目标建立在我们的研究结果在本研究的第一阶段，他们将扩大我们的理解湍流结构使用的测量技术，提供更高的空间和时间分辨率。我们的第一个目标是澄清的不确定性缩放的结构湍流属性使用小型HWA和三维高分辨率剖面测量。第二个目标是量化大尺度相干结构的运动学和动力学。在本研究的第一阶段，在预乘能谱中已经确定了这种结构的长度尺度、能量含量和壁法线位置。在第二阶段，我们将提取低阶子空间的高维湍流，从2D和3D时间分辨测量的移动参考框架上应用特征DMD（与TU柏林，J. Sesterhenn合作）。具有长寿命的提取子空间的优化组合将形成降阶模型，其容纳已知负责形成谱峰的结构。在不存在小尺度结构的情况下，研究各组结构的寿命和时空演化。这将允许确定这些结构如何有助于湍流特性，如TKE预算，雷诺应力和粘性剪切应力。

The present work aims at investigation of turbulent pipe flow at high Reynolds numbers and low Mach numbers. During the recent years there has been an increasing interest in observation and understanding of large scale turbulent coherent structures, which are commonly known as Large and Very Large Scale Motions (LSM and VLSM). Nevertheless, a solid definition of their nature and vivid understanding of their evolution is still incomplete. Therefore, this study will focus on clarifying the nature and origin of LSM and VLSM as well as describing and identifying them in a quantitative manner. To this end, experiments and numerical computations (together with possible partners within the SPP) will be performed and matched as closely as possible. Experiments at Cottbus Large Pipe Test Facility (CoLa-Pipe), which was used successfully along the first phase, will be conducted at bulk Reynolds numbers of 6x10E4 ≤ Re b ≤ 1x10E6 (based on pipe diameter D and bulk velocity Ub) and Mach numbers Ma < 0.23, measuring turbulent flow properties using miniaturized Hot Wire Anemometry (HWA), high speed Particle Image Velocimetry (PIV) and Shake The Box (STB) particle tracking technique (in collaboration with DLR, A. Schröder).This proposal aims at two prominent objectives. Both objectives build on our findings in the first phase of this study and they will expand our understanding of turbulent structures using the measurement techniques which provide higher spatial and temporal resolutions. Our first goal is to clarify the uncertainties concerning scaling of structural turbulence properties using miniaturized HWA and 3D high resolution profile measurements. The second goal is to quantify the kinematics and dynamics of large-scale coherent structures. The length scales, energy contents and wall-normal locations of such structures have been already determined in pre-multiplied energy spectra during the first phase of this study. In the second phase, we will extract low order subspaces of highly dimensional turbulent flow, from 2D and 3D time-resolved measurements on a moving frame of reference by applying a Characteristic DMD (in collaboration with TU Berlin, J. Sesterhenn). Optimized combinations of extracted subspaces with long life times will form reduced order models, which accommodate structures that are known to be responsible for the formation of the spectral peaks. Life times and spatio-temporal evolutions of each group of structures will be studied in absence of small-scale structures. This will allow to determine how such structures contribute to turbulence properties such as TKE budgets, Reynolds stress and viscous shear stress.