Analysis of unsteady flow around an axial circular cylinder of critical geometry using combined synchronous measurement in magnetic suspension and balance system

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

“…The result appears as lateral force fluctuations acting on the cylinder. Relatively large fluctuations around the fluctuation frequency of the large-scale vortex shedding were also observed in the PSD for L/D = 2.0, which was not mentioned by Yokota et al (2021). Note that the fluctuation level is smaller than in the case of L/D ≤ 1.5.…”

“…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.…”

“…Simultaneously, the pressure field at the base of the cylinder fluctuates, which appears as a drag force fluctuation acting on the cylinder. In contrast, the power spectral density (PSD) distribution shown by Yokota et al (2021) indicates that the amplitude of the fluctuation due to the recirculation bubble pumping is smaller for the reattaching flow at L/D ≥ 1.5 compared with the case of the non-reattaching flow. Moreover, Nonomura et al (2018) confirmed that the fluctuations in the low-frequency region around f = 1 Hz (St = 0.02) were smaller only for L/D = 2.0 from the PSD of the pressure fluctuations at the centre of the cylinder base for L/D = 0.75-2.0.…”

“…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.…”