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

• Published in: Experiments in fluids 2021, Vol.62 (1), Article 15
• Main Authors: Yokota, Sho, Ochiai, Taku, Ozawa, Yuta, Nonomura, Taku, Asai, Keisuke
• Format: Article
• Language: English
• Subjects: Aerodynamic characteristics; Aerodynamic forces; Aerodynamics; Base pressure; Circular cylinders; Computational fluid dynamics; Diameters; Drag; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Fineness; Fluid flow; Fluid- and Aerodynamics; Heat and Mass Transfer; Magnetic levitation; Research Article; Reynolds number; Support interference; Unsteady flow; Velocity distribution; Vortex shedding; Wind tunnel testing; Wind tunnels
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-020-03101-7

The wake structure of a freestream-aligned circular cylinder and its aerodynamic characteristics were investigated using a magnetic suspension and balance system (MSBS), which can levitate a model to eliminate support interference. The objectives of the present study were to investigate the flow field around a freestream-aligned circular cylinder and to clarify its effect on the aerodynamic force and base pressure. Experiments were conducted using a 0.3-m MSBS for support-free wind tunnel tests. Six models with fineness ratios (length to diameter, L / D ) of 1.0, 1.25, 1.5, 1.75, 2.0, and 2.25 were used. The freestream velocity was set to 10 and 20 m/s, which correspond to Reynolds numbers based on model diameters of 3.3 × 10 4 and 6.7 × 10 4 , respectively. The velocity field, aerodynamic force, and base pressure were measured for each freestream-aligned circular cylinder. Two characteristic fluctuations with frequencies of St < 0.05 and St ≈ 0.13 were observed in a nonreattaching flow field. A low-frequency axisymmetric fluctuation related to the drag force and base pressure was observed in the axial direction. A high-frequency antisymmetric fluctuation related to the lift force was observed in the radial direction. These features are in good agreement with those of both recirculation-bubble pumping and vortex shedding observed in the wake of a disk reported in previous studies (Berger et al., J Fluids Struct 4(3):231–257, 1990; Yang et al., Phys Fluids 27(6):064101, 2015). Graphic abstract