Experimental study on turbulent pipe flow

Abstract: Fully developed turbulent pipe ows have been studied experimentally for more than a century and for more than two decades by means of Direct Numerical Simulations, nonetheless there are still unresolved and of fundamental nature issues. Among those are the scaling of the mean velocity pro le or the question whether the near-wall peak in the variance pro le is Reynolds number invariant. In this thesis new experimental results on high Reynolds number turbulent pipe ows, obtained by means of hot-wire anemometry, are carefully document and results are presented, thereby extending the Reynolds number range of an available in-house experimental database (Sattarzadeh 2011). The main threads of this thesis are the spatial resolution eects and the Reynolds number scaling of wall-bounded ows and were investigated acquiring the measurements with probes of four dierent wire-lengths at dierent Reynolds numbers covering the friction Reynolds number range of 550 <R+< 2 500. The small viscous length-scales encountered required a high accuracy in the wall-position. Therefore, a vibration analysis of the probe exposed to the ow was performed on two dierent traversing systems and on several probeholder/ probe con gurations, proving that the vibrations of the probe can be large and should be taken into account when choosing the traverse system and probe-holder geometry. Results of the hot-wire velocity measurements showed that when accounting for spatial resolution eects, a clear Reynolds number eect on the statistical and spectral quantities can be observed. The peak of velocity variance, for instance, appeared to increase with the Reynolds number and the growth seems to be justi ed from the increase of the low frequency modes. This result together with the appearance of an outer peak located in the low frequency range at higher Reynolds numbers suggests that the increase of the peak of the velocity variance is due to the inuence that the large-scale motions have on the near-wall cycle of the velocity uctuations. As a side results of the velocity measurements, temperature, i.e. passive scalar, mean and variance pro le were obtained by means of cold-wire anemometry. Also here, clear spatial resolution eect on the temperature variance pro le could be documented.