A study of velocity fields in the near wake of a wavy (varicose) cylinder by LDA

The near wake of a wavy cylinder has been experimentally investigated using a Laser Doppler Anemometer. The experiments were carried out in a low speed wind tunnel having a 0.6 × 0.6 m cross-section and a free-stream turbulence intensity less than 0.2%. The Reynolds numbers, based on the free-stream velocity and the nominal cylinder diameter, vary from about 3.0 × 10³ to 9.0 × 10³. The mean and fluctuating velocity components are presented in the streamwise, spanwise and transverse direction, respectively. The results indicated that the long vortex formation length of the wavy cylinder is the main reason of drag reduction and suppression of vibration. The results also show that the spanwise flow is from the saddle plane towards the nodal plane on both sides of the wavy cylinder. Furthermore, the cross-stream profiles of the mean streamwise velocity show the wake in the vortex formation region of the saddle plane is wider than that of the nodal plane. The velocity distributions also provide an important database for the validation of turbulence modeling and 3-D numerical simulations.