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

点击翻译按钮获取中文摘要

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.