Experiments on the stability of two types of spiral flow

Abstract

An experimental study has been carried out of spiral flows between concentric rotating cylinders when gap between them is small. The axis of the cylinders is vertical and a radial thermal gradient may be applied between the cylinders. The resulting convective flow is axial and has a cubic profile symmetric about the center of the gap. Another form of spiral flow results from the application of an axial pressure gradient. This flow has a parabolic profile. Each type of flow and combinations of the two are used to study the effect of the profile on the stability with respect to the transition to Taylor vortices. It is found that the position of the inflection point of the profile is very important in determining the stability curve. When the parabolic flow is large enough to displace the inflection point beyond the region of the gap, the stability curve is determined by the parabolic flow and is uneffected by the thermal gradient. This holds true even when the Rayleigh number becomes comparable to the Taylor number. Data is presented for the stability curve in the region of angular velocities −2 < Ω 2 Ω 1 < 0.92 in the range of thermal gradients −25°C/cm < δT < 25°C/cm and in the range of axial Reynolds numbers 0 ≦ R < 200. The wave form of the disturbance is also described.