Highly resolved spatio-temporal measurements of the near-wall turbulent pipe flow up to Re_tau = 45 000

Kurzfassung

Acombination of low and high repetition 2d2c PIV measurements at a pixel magnification exceeding the viscous scale were performed in the near-wall region (0 < y < 20mm) of the turbulent pipe flow of the CICLoPE Long Pipe facility to extend upon similar measurements performed in 2016. The time resolved imagery was processed with a multi-frame correlation scheme to achieve unprecedented velocimetry data with sub-viscous scale resolution. The acquired data base provides converged statistics of the velocity variances and at the same time yields corresponding spectral densities across a wide frequency range by combining data acquired at different sampling rates. Both the inner and outer streamwise turbulence peaks are captured with an underestimation at the highest shear Reynolds number of Re_tau = 44700 caused by spatial filtering. The inner turbulence peak height follows the trend of Reynolds number dependent growth predicted by DNS and previous hot wire measurements turbulent pipe flow but is lower than for flat plate boundary layer. Spectral densities in the near wall region were found to be essentially universal across the studied Reynolds number range. Further improvement is demonstrated by processing the images with a 2d Shake-the-Box (STB) Lagrangian particle tracking scheme