Flow characteristics around extremely low fineness-ratio circular cylinders

Unsteady large-scale wake structure behind levitated free-stream-aligned circular cylinder

“…This symmetry-broken flow was also observed in the ground-mounted Ahmed model wake (Grandemange et al 2013). The appearance of symmetry-broken modes of RSP and RSB modes in the wake of the free-stream-aligned circular cylinder is expected, but has not been discussed in the studies on the turbulent wake of the cylinder at L/D ≥ 0.3 (Prosser & Smith 2016;Nonomura et al 2018;Shinji et al 2020;Kuwata et al 2021;Yokota et al 2021). The relationship between the characteristic flow structures occurring in the wake and the aerodynamic forces acting on the cylinder has been well discussed in their studies.…”

“…This structure was also adopted in the previous studies (Yokota et al 2021(Yokota et al , 2022(Yokota et al , 2023Tashiro et al 2022). On the other hand, another configuration can be adopted when the fineness ratio is low (Kuwata et al 2021;Inomata et al 2023). The CCD line sensors capture the surface of the model illuminated by the LED light sources, and the images are used to detect the edges of the model and the black band painted on the model.…”

“…Studies on the free-stream-aligned circular cylinder have been conducted both numerically (Yang et al 2014(Yang et al , 2015Prosser & Smith 2016;Tian et al 2016Tian et al , 2017Gao et al 2018;Nidhan et al 2020) and experimentally (Higuchi et al 2006;Johansson & George 2006a,b;Higuchi, Sawada & Kato 2008;Bobinski, Goujon-Durand & Wesfreid 2014;Shinji et al 2020;Kuwata et al 2021;Yokota et al 2021;. The flow around the free-stream-aligned circular cylinder is classified into two main types based on the time-averaged velocity field.…”

“…The velocity measurement planes in these previous studies can be divided into two main categories. The first is the case where the measurement plane is set parallel to the free stream through the cylinder axis, which has been adopted by Higuchi et al (2008), Yokota et al (2021Yokota et al ( , 2022Yokota et al ( , 2023 and Kuwata et al (2021). This plane can capture fluctuations due to recirculating bubble pumping, but obviously not the azimuthal fluctuations in the position of the large-scale vortex structure.…”

“…Discussion between phenomena is provided mainly from the results of mode decomposition for the measured velocity data. Our group has discussed the phenomena in the wake by adapting two-dimensional two-component velocity field measurements in a plane parallel to the free stream and a pressure measurement system using wireless transmission to experiments with the MSBS (Nonomura et al 2018;Shinji et al 2020;Kuwata et al 2021;Yokota et al 2021). The present study is the first experience of measuring a two-dimensional three-component velocity field in an interference-free condition, and the results of the velocity field in a plane perpendicular to the free stream are considered to improve our understanding of the wake phenomena.…”