Passive control on flow past a circular cylinder with bionic nylon wires

We investigated the control effectiveness and mechanism of the control of the circular cylinder flow field using bionic nylon wires inspired by bird feathers by wind tunnel tests. In this experiment, at a Reynolds number of 2.67 × 10⁴, the bionic nylon filament was arranged at the front station of the cylinder and the length ratio L/D between nylon wire length and cylinder diameter was used as the characteristic parameter. The surface pressure measurement system was used to obtain the pressure coefficients around the cylinder to analyze the aerodynamic forces acting on the cylinder. The two-dimensional flow field information of the cylinder was obtained by a high-speed Particle Image Velocimetry (PIV) measurement system, and the Proper Orthogonal Decomposition (POD) was used to obtain the instantaneous and time-averaged characteristics of the flow field. The results show that at L/D < 0.6, the control effectiveness of nylon wires is limited because the nylon-induced vortex structures cannot reach the wake field. At L/D > 1.0, the nylon wires can significantly reduce the turbulent kinetic energy and Reynolds stress of the cylindrical wake field and suppress the lift and drag coefficient distributions around the circular cylinder. And at high values, nylon wires can inhibit the interaction between shear layers and thus change the von Kármán vortex shedding pattern of the cylinder.