SPANWISE COUPLING OF CELLULAR STRUCTURES IN 2-D AND TAPERED CIRCULAR CYLINDER WAKE UNDER ACOUSTIC EXCITATION

The wake behind a two-dimensional (2-D) and tapered circular cylinder was locally excited by acoustic waves to invesigate the spanwise coupling of cellular shedding vortices by means of hot-wire measurements. The experiments were conducted in a low-speed wind tunnel, with the operating Reynolds number based on the mean diameter fixed at 1·0×104. The cellular structure of the shedding vortices in the wake behind a 2-D circular cylinder can be enhanced and locked in to the artificial perturbations. Three lock-in regions with different ratios of the response frequency to the excitation frequency were identified. As for the wake behind the tapered cylinder, the cellular distribution of the natural shedding frequency was significantly restored when the acoustic waves were introduced at a reasonable level of excitation. In addition, the length of the spanwise lock-in region extending leftward and rightward from the exciting slot would reach a saturated value and the saturated lock-in remains almost the same for the three slot locations tested.