Behaviour of Energetic Coherent Structures in Turbulent Pipe Flow at High Reynolds Numbers (PDF)

In this thesis, coherent turbulent structures in turbulent pipe flow are investigated at relatively high Reynolds numbers and study their association in both total kinetic energy and Reynolds shear stress. Experimental investigations have been performed in Cottbus Large Pipe test facility (CoLaPipe) for pipe flow over a wide range of Reynolds number 8 x 104 ≤ ReD ≤ 1 x 106, located at the Aerodynamics and Fluid Mechanics Department, Brandenburg University of Technology Cottbus- Senftenberg (BTU). The first part of the thesis focuses on determining the contribution of the coherent structures using one-dimensional spectral analysis and assessing the structures behaviour in the outer region of pipe flow using high spatial resolution Hot-wire measurement up to 30kHz. The results of the power and pre-multiplied spectrum of stream-wise velocity indicate that the wavelength value of very large scale motions (VLSMs) acquires 19R at a maximum Reynolds number range ReD=1 x 106 (Reτ =19000). On the other hand, large-scale motions have a wavelength value of 3R over different Reynolds number range. Regarding the identified wavelength values, it is observed that contribution to energy for structures greater than 3R carries 55% of total kinetic energy. In addition, temporal-spatial resolution using the High-speed PIV measurements has been performed in CoLaPipe to estimate the contribution magnitude of stream-wise/wall-normal velocity fluctuations to total kinetic energy and Reynolds shear stress in the logarithmic and outer layer.