STABILITY OF THE FLOW IN A HELICAL TUBE

The flow in a helical tube of small curvature and its linear stability are theoretically investigated for a wide range of the torsion parame ter beta(0), which is defined as beta(0) = lambda/root 2 delta with th e dimensionless torsion lambda and curvature delta. It is shown that t he torsion has a destabilizing effect on the flow. The critical Dean n umber at the onset of unstable flow first decreases as beta(0) increas es, reaches a minimum at beta(0) approximate to 1.4, and then increase s again. The minimum Dean number is about 600. The stability character istics obtained are favorably compared with those in the previous expe riment by Yamamoto et al., Fluid Dyn. Res. 16, 1995. (C) 1998 The Japa n Society of Fluid Mechanics Incorporated and Elsevier Science B.V. Al l rights reserved.