On Shedding Frequency and Aerodynamic Characteristics of a Rotating Wire-wrapped Cylinder 2020-01-0028
Numerical investigations of shedding frequency of rotating smooth and wire-wrapped cylinders, placed in steady flow have been performed. The freestream mean velocity was 10 m/sec. and the smooth cylinder diameter was 5 cm, which corresponds to an approximate Reynolds number based on cylinder’s diameter of 3.2x104. The wire wrapped cylinder had a wire diameter of 5 mm and the ratios of pitch spacing to the cylinder diameter, p/D, was 1.0. The cylinder length to diameter ratio was 20. The rotation rate (λ), the ratio of axial tangential mean velocity at the cylinder’s surface to the free stream mean velocity was 2.0. To obtain the shedding frequency, numerical probes were placed at 3D downstream, 0.5 D above the centerline, spaced at 0.5D along the spanwise direction for obtaining instantaneous axial velocity and shedding frequencies were obtained from spectra of the axial velocity.
Results indicate that the lift for the wire-wrapped cylinder is nearly 150% of that of the smooth cylinder, however, it has higher drag force. The lift to drag ratio for the smooth rotating cylinder is 3.89, while for the rotating wire-wrapped cylinder is 3.54. Details of the flow indicates wire-wrapping reduces coherency and increases phase angle of vortices, resulting in increased lift.
Experimental verifications of the numerical results were performed in an open circuit wind tunnel at the same freestream mean velocity. The cylinder dimeter was 2.54 cm and for the wire-wrapped cylinder, p/D and d/D were respectively 1.0 and 1.2. Experimental results indicate similar trend as the numerical results, with wire-wrapping reduces the shedding oblique angle and with rotation, reduced peak energy, breaking down the large eddies into smaller eddies of different frequencies.
Hamid R. Rahai
California State University-Long Beach