Abstract
Time–frequency distributions of axial turbulence velocities of spiral pipe flow and typical turbulent flow have been clearly decomposed in a range from low frequency level (low wavenumber) to high frequency level (high wavenumber) by means of discrete wavelets transform and its auto-correlation. As a result, fluctuation levels of spiral flow are extremely low as compared with those of typical turbulent flow. Moreover, spiral flow has a time periodicity on wavelets Level 3 at a central point and on Levels 1 and 2 near wall of a pipeline. However, typical turbulent flow does not have the tendency. Spiral flow has an orderly radial velocity, which contributes to the lower fluctuation level and the time periodicity at the central point. The mean velocity of the air flow in the vertical pipe was 1.50 m/s, and Reynolds number was about 4200. The originality of this paper lies in applying discrete wavelets transform and its auto-correlation to analyzing the stable spiral flow motion in time–frequency dimension.
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