Numerical study on secondary flow characteristics after dual stepped cylinder at low reynolds number

Abstract

A dual stepped cylinder consists of two small slender cylinders of the same diameter being co-axially connected by a large one. Flow travelling over the step surface can generate strong ‘end flow’, which goes and develops downstream, approaching the large cylinder. This ‘end flow’, defined as ‘downwash’, gives rise to the impact of three-dimensional vortex shedding in the wake area, which is numerically investigated in the present paper at the Reynolds number of 150 (Reynolds number is estimated based on the diameter of the large cylinder.). Apart from that, the vertical velocity in the wake goes downstream, at the same time transferring up and down periodically. This periodic vertical flow, together with the ‘end flow’, can be attributed to ‘secondary flow’. In the present paper, flow passing two stepped cylinders with diverse diameter ratios (D/d) are modelled numerically. Results about the corresponding vertical velocity and ‘end flow’ are comprehensively studied. The relationship between velocity field and vortex structures in the wake is also investigated in this present paper.