Characteristics of near wake behind a circular cylinder with serrated fins (III): mechanism of velocity recovery

The characteristics of near wakes of circular cylinders with serrated fins are investigated experimentally using a hot-wire anemometer for various freesteam velocities. Near wake structures of the fin tubes are observed using a phase average technique. With increasing fin height and decreasing fin pitch, oscillation of steamwise velocity increases. While oscillation of lateral velocity decreases. The time averaged V-component velocity distribution of the finned tube is contrary to that of the circular cylinder due to the different strength of entrainment flow. This strength is affected by the distance of U/Uo=1.0 contour lines. U/Uo=1.0 contour line approaches to the wake center line when the fin density is increased. When the distance between U/Uo=1.0 contour lines comes close, the shear force should be increased and the flow toward the wake center line can be more strengthened because of the shear force. Factors related to the velocity recovery in the near wake of the finned tube are attributed to the turbulent intensity, the boundary layer thickness, the position and strength of entrainment process