An experimental investigation of drag and noise reduction from a circular cylinder using longitudinal grooves

Aerodynamic and aeroacoustic characteristics of a cylinder with longitudinal grooves were studied in an anechoic wind tunnel, emphasizing on drag and noise attenuation. The parallel mounted load cells and a single microphone measured the aerodynamic resistance and noise of a circular cylinder with longitudinal grooves at Reynolds number ranging from 5.84 × 104 to 8.48 × 104, covering the flow regimes from the sub-critical to the post-critical states. The results show that longitudinal grooves can effectively trigger the boundary-layer transition started at a Reynolds number around 5.84 × 104, causing the so-called drag crisis. During the transition process, a drag reduction over 50% and a maximum noise attenuation over 15 dB can be achieved by longitudinal grooves. The variations of the drag and noise are linked to the near-field flow measurements using hot-wire in different regimes, enhancing our understanding of the problem.