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Wind and Structures
  Volume 23, Number 2, August 2016, pages 127-142

The turbulent wake of a square prism with wavy faces
Y.F. Lin, H.L. Bai and Md. Mahbub Alam

    Aerodynamic effects, such as drag force and flow-induced vibration (FIV), on civil engineering structures can be minimized by optimally modifying the structure shape. This work investigates the turbulent wake of a square prism with its faces modified into a sinusoidal wave along the spanwise direction using three-dimensional large eddy simulation (LES) and particle image velocimetry (PIV) techniques at Reynolds number ReDm = 16,500 22,000, based on the nominal width (Dm) of the prism and free-stream velocity (U). Two arrangements are considered: (i) the top and bottom faces of the prism are shaped into the sinusoidal waves (termed as WSP-A), and (ii) the front and rear faces are modified into the sinusoidal waves (WSP-B). The sinusoidal waves have a wavelength of 6Dm and an amplitude of 0.15Dm. It has been found that the wavy faces lead to more three-dimensional free shear layers in the near wake than the flat faces (smooth square prism). As a result, the roll-up of shear layers is postponed. Furthermore, the near-wake vortical structures exhibit dominant periodic variations along the spanwise direction; the minimum (i.e., saddle) and maximum (i.e., node) cross-sections of the modified prisms have narrow and wide wakes, respectively. The wake recirculation bubble of the modified prism is wider and longer, compared with its smooth counterpart, thus resulting in a significant drag reduction and fluctuating lift suppression (up to 8.7% and 78.2%, respectively, for the case of WSP-A). Multiple dominant frequencies of vortex shedding, which are distinct from that of the smooth prism, are detected in the near wake of the wavy prisms. The present study may shed light on the understanding of the underlying physical mechanisms of FIV control, in terms of passive modification of the bluff-body shape.
Key Words
    square prism; sinusoidal wavy face; passive control
Y.F. Lin: Shenzhen Key Laboratory of Urban Planning and Decision Making, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China;
Parsons Brinckerhoff (Asia) Ltd., Hong Kong
H.L. Bai: Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
Md. Mahbub Alam: Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China


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