Evidence for instabilitywaves in the velocityfield of a fully developed turbulent channelflow
Abstract
The results from hot film measurements and quantitative visual investigations, performed in the turbulent flow of an oilchannel at a low Reynolds number (Re = 8000), are discussed. The main result of the hot film measurements is the power spectrum of the vcomponent of the fluctuating velocity. The power spectrum has regular maxima and minima. The frequencies corresponding to the maxima of the power spectrum are plotted as a function of the order n of the maxima. This graph demonstrates that the frequencies of the maxima are the harmonics of a fundamental frequency which are determined to be about 0.15 Hz. An estimation shows that the fundamental frequency is of the same order of magnitude as the roughly calculated unstable TollmienSchlichting frequencies of the mean turbulent velocity profile. This fundamental frequency is interpreted as the most excited frequency of TollmienSchlichtinglike instability waves. The harmonics are believed to be due to a nonlinear amplification of the primarily excited instability waves. The evidence of regular oscillations in the nearwall region of the fully developed turbulent flow from the visual studies is examined.
 Publication:

In AGARD Turbulent Boundary Layers 5 p (SEE N8027647 1834
 Pub Date:
 January 1980
 Bibcode:
 1980tbl..agarQ....H
 Keywords:

 Channel Flow;
 Flow Stability;
 Flow Velocity;
 Turbulent Flow;
 Frequency Stability;
 Harmonics;
 HotFilm Anemometers;
 Power Spectra;
 Velocity Distribution;
 Fluid Mechanics and Heat Transfer