On the instability of a flow in an axially rotating pipe(2nd reptrt, Characteristics of a spiral wave).

Abstract

An experimental study of the instability of a flow in an axially rotating pipe is performed by means of LDV and flow visualization technique. It is found that the velocity of the rotating pipe flow fluctuates like a sine wave at first, then its fluctuating pattern becomes somewhat sawtooth wave form as the spiral wave appears. At the downstream section, another fluctuating component appears in the velocity, which interferes with the first appeared component, then the fluctuation becomes the one which has broad band spectral components. There is a close analogy between this spectral evolution and that of a Taylor-Couette flow. Deformation of the velocity distribution is obtained from the velocity fluctuating pattern and its phase, and the structure of the spiral wave is considered. The strength and the azimuthal wavenumber and the angular velocity of the spiral wave obtained from the velocity data is confirmed by the flow visualization. Flow visualization also shows that the axial wavelength of the spiral wave becomes large with an increase of the swirl ratio, but its length changes with time at very high swirl ratio.