Fluid flow in a helical pipe

Without simplifying the N-S equations of Germano's([5]), we study the flow in a helical circular pipe employing perturbation method. A third perturbat ion solution is fully presented. The first- second- and third-order effects of curvature kappa and torsion tau on the secondary flow and axial velocit y are discussed in detail. The first-order effect of curvature is to form t wo counter-rotating cells of the secondary flow and to push the maximum axi al velocity to the outer bend. The two cells are pushed to the outer bend b y the pure second-order effect of curvature. The combined higher-order (sec ond-, third-) effects of curvature and torsion, are found to be an enlargem ent of the lower vortex of the secondary flow at expense of the upper one a nd a clockwise shift of the centers of the secondary vortices and the locat ion of maximum axial velocity. When the axial pressure gradient is small en ough or the torsion is sufficiently larger than the curvature, the location of the maximal axial velocity is near the inner bend. The equation of the volume flux is obtained from integrating the perturbati on solutions of axial velocity. From the equation the validity range of the perturbation solutions in this paper can be obtained and the conclusion th at the three terms of torsion have no effect on the volume flux can easily be drawn. When the axial pressure gradient is less than 22.67, the volume f lux in a helical pipe is larger than that in a straight pipe.