Stabilization of vortex shedding in a three dimensional flow in a circular pipe.

In this paper, a general condition for regular vortex shedding in a 3-dimensional flow is proposed: local shedding frequency must remain constant along the span of the bluff body. The local shedding frequency is proportional to the ratio of the local velocity to the local width of bluff body, and the nondimensional coefficient is called the Strouhal number. This condition requires a constant ratio of local velocity to local width. A uniform velocity profile (2-dimensional flow) is a special case which meets the condition. Consequently, new vortex generators with 3-dimensional shape which satisfy the condition in pipe flow are obtained. As experimental results, new generators give stronger and more regular vortex shedding. This improvement confirms the condition to be right. Furthermore, it may be applied to shed regular vortices in arbitrary 3-dimensional flow. (from English abstract)