The effect of torsion on primary and secondary laminar flow in a curved annular sector duct with a finite pitch has been studied. Six parameters have been identified as major variables describing the flow pattern. Results of this study indicate that torsion will significantly change the secondary flow behavior, vary the vortex pattern, and destroy the symmetry of the primary and secondary flows. For ducts with a centerline parallel to the normal direction, torsion will rotate the high axial velocity contours to one side and slightly change the axial velocity gradient near the solid wall. For the ducts with a centerline in a bi-normal direction, torsion may significantly increase the axial velocity gradient along the solid wall, considerably increasing the friction coefficients. The results also indicate that the torsion effect may be enhanced by increasing the curvature and axial pressure gradient. However, the torsion effect does not seem to be sensitive with changes to the sector angle and the radius ratio.
