The analysis of coherent flow structures in turbulent boundary layers along flat plates with zero pressure gradient is intensely studied due to the vast scientific and technological interest for this type of canonical flow. Consensus exists that vortices are the building blocks of the coherent structures but the exact form or generation and subsequent dynamics of the vortices is still under debate. In the last decade, the observation of so called coherent superstructures has gained strong attention because they are almost ten times longer than the main spatial scales in the flow. It is assumed that these superstructures are of immense importance at high Reynolds numbers. However, quantitative measurements of these structures is difficult due to their large stream-wise spatial extent. Within this project, a turbulent boundary layer flow will be investigated at Re_theta up to 80000 to examine the characteristic features of the superstructures and their interaction with other known coherent structures such as low-speed streaks, for instance. Furthermore, it is the aim of the project to demonstrate the effect of this interaction on the production of turbulence and the dynamics of the wall shear stress and thus skin friction. The analysis will be performed in the 22 m long test section of the Atmospheric Windtunnel Munich (AWM) with sophisticated optical measurement techniques such as long-range microscopic PTV, multiplane stereo PIV, time resolved tomographic PIV / PIV. Due to the expected dimensions of the superstructures, measurement volumes of several meters in length are required. This is rather challenging, not only from the experimental point of view but, also from the evaluation, analysis and visualization perspective due to the large data sets generated from these types of measurements.
 
Cooperations: DLR Göttingen, University of Stuttgart, Princeton University
 
Person in charge: Dr. Matthew Bross
 
Funder: German Research Foundation (DFG) within the Priority Program 1881, Turbulent Superstructures
 
Publications:
  • Bross M, Kähler CJ (2017) Three Dimensional Near-Wall Events in an Adverse Pressure Gradient Boundary Layer. 10th International Symposium on Turbulence and Shear Flow Phenomena (TSFP10), Chicago, USA, July 6-9
  • Bross M, Kähler CJ (2016) Time-Resolved 3D-PTV Analysis of Near Wall Reverse Flow Events in APG Turbulent Boundary Layers. 18th International Symposium on the Applications of Laser and Imaging Techniques to Fluid Mechanics, Lisbon, Portugal, July 4-7