Coherent organizational states in turbulent pipe flow at moderate Reynolds numbers

Turbulent pipe flow is still an essentially open area of research, boosted in the last two decades by considerable progress achieved both on experimental and numerical frontiers, mainly related to identification characterization coherent structures as basic building blocks turbulence. It has been a challenging task, however, detect visualize these states. We address, means stereoscopic particle image velocimetry, that issue with help large diameter (6 inches) loop, which allowed us probe for states at various moderate Reynolds numbers (5300 < Re 29000)). Although have observed regimes around laminar-turbulent transition (Re $\approx$ 2300) also high number 35000), their existence had not yet experiment. By conditionally averaging fields respect dominant azimuthal wavenumber streamwise velocity streaks, we able uncover ten well-defined patterns. turns out, remarkable phenomenon, occurrence probabilities total modes do change varied. Their are noted be reasonably well described Poisson distribution, suggests low-speed streaks created process circular geometry.