Drag reduction and optimization on a sphere with the effect of Lorentz force

• Published in: Ocean engineering 2023-07, Vol.280, p.114836, Article 114836
• Main Authors: Yao, Weiguang, Zhang, Hui, Jiang, Daiwen, Gui, Mingyue, Zhao, Zijie, Chen, Zhihua
• Format: Article
• Language: English
• Subjects: Drag reduction; Flow control; Lorentz force; Optimal location; Sphere
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2023.114836

The flow of a weakly conductive fluid (i.e. seawater) can be controlled by Lorentz force, which holds promising applications in drag reduction. In this paper, the drag reduction on a stationary sphere in the weakly conductive fluid with the Lorentz force on the sphere surface are numerically investigated at Re = 300. The relations among the vortex structures, the hydrodynamic forces, and the effects of drag reduction are discussed before and after the application of the Lorentz force. The results indicate that the fluid near the surface of the sphere is accelerated with the application of Lorentz force. Therefore, the flow separation on the rear surface of the sphere is suppressed, and the periodic shedding mode of hairpin vortices is replaced by the steady double-thread wake structure. Meanwhile, the increase of momentum near the sphere improves the capability to overcome the adverse pressure gradient. Therefore, the pressure on the leeward side of the sphere increases, and then the effect of drag reduction is achieved. Moreover, the effects of drag reduction are distinct with the different locations (θm) of the applied Lorentz force, which reaches the maximum drag reduction rate together with the maximum drag reduction efficiency for θm = 90°. •The relations are revealed among the characteristic structures, drag reduction, and the parameters of Lorentz force.•The increase of the pressure on the leeward side of the sphere by Lorentz force is the key of drag reduction.•The optimal location is found based on the control mechanism with the different locations of the applied Lorentz force.