Flow field of a curved cylinder

Abstract

Flow field of a curved cylinder was experimentally investigated for Reynolds numbers of 20,000 and 50,000. Tests consisted of flow visualization in a wind tunnel and a water tunnel, wake total pressure surveys and hot wire anemometry. Surface flow topology suggested a nodal, saddle and mixed nodal-saddle types of attachment that depended on the azimuthal orientation of the cylinder. The nature of attachment also influenced the spanwise distributions of foci structures and their role in introducing three-dimensionality in the immediate wake. Flow visualization in the water tunnel revealed that the length of a vortex formation region also increased steadily with the azimuthal orientation. A symmetric shedding of vortices was observed with a saddle type of attachment. Wake mean velocity profiles showed that the velocity defect and therefore the drag of a curved cylinder was minimum for nodal, and maximum for saddle type of attachment. Nomenclature of the wake was compared with asymptotic profiles and equilibrium parameters. Approach to self preservation, similarity, and other features are discussed. Nomenclature b Half wake width D Cylinder diameter f Vortex shedding frequency U Mean axial velocity -Uo, edge velocity U^, free-stream velocity St Strouhal number fD/U Re Reynolds number UD/v RCC Right circular cylinder W Wake velocity defect (Wo, centerline defect) X,Y,Z Axial, transverse and spanwise coordinates 0 Momentum thickness (p Flow attachment angle i) Kinematic viscosity