Experiments on large-scale structures in fully developed turbulent pipe flow

The experimental results reported in present paper represent contributions from the Cottbus large pipe facility to DFG-priority program SPP 1881: Turbulent Superstructures. Fundamental questions regarding turbulence statistics and structures in fully developed turbulent pipe flow were addressed, utilizing thermal and optical measuring techniques integrated into the pipe facility. The facility enables unique in-situ calibration for the hot-wire probe and it has full optical access that allows performing Particle Image Velocimetry and 3D Lagrangian Particle Tracking measurements, resulting in consistent and accurate pipe flow data. A streamwise-spanwise field of view up to ≈ 20×2 pipe radii has been set for both optical techniques with 4–8 high resolution cameras for a friction Reynolds number range of 8⋅102≤R+≤18⋅103. The setup enabled field of measurements with an unprecedented dynamic range in turbulent pipe flow at high Reynolds numbers with spatial resolution better than 1 vector/mm. Proper Orthogonal Decomposition and Shake-The-Box algorithm were used, highlighting energy contents of the large-scale motions in fully developed turbulent pipe flow regime.