Journal of Fluids and Structures 81 (2018) 738–760 Contents lists available at ScienceDirect Journal of Fluids and Structures journal homepage: www.elsevier.com/locate/jfs Flow control around a circular cylinder with swinging thin plates Babak Bagherzadeh Chehreh, Khodayar Javadi * Flow Control Research Lab, Department of Aerospace Engineering, Sharif University of technology, Iran article info Article history: Received 10 November 2017 Received in revised form 25 May 2018 Accepted 12 June 2018 Keywords: Aerodynamic instability Pressure field fluctuation Circular cylinder Splitter plate Strouhal number abstract Flow around a 2D circular cylinder with attached swinging thin splitter plates is numer- ically investigated. The ratio of the plates’ length to the cylinder diameter is 1 ( L D = 1) where L is the Plates’ length and D is the cylinder diameter. The plates are attached at ±55 degrees (trigonometric angle) downstream and are forced to oscillate at different ratios of the natural vortex shedding frequencies with magnitudes of FR = 0.75, 1, 1.25, 1.5 and 2. The oscillation amplitude ‘‘α’’ as the other main variable ranges from 10 to 18 degrees. Two- dimensional simulations are carried out at the Reynolds number 100, and then extended to higher Reynolds number of 200. The results show that in certain configurations, an in-phase vortex-shedding pattern is dominant and the oscillatory nature of the lift force completely vanishes. Different flow patterns are observed and classified as well. The effects of the splitter plates’ oscillation on the lift and drag forces, flow patterns and vortex shedding frequencies are also discussed to develop a link between different flow patterns and the acting lift force on the cylinder. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction For decades, vortex dominated flows have been the subject of study for engineers and researchers interested in vortex shedding phenomenon. When a fluid flows over a non-streamlined body like a circular cylinder, two symmetrically placed attached eddies take form on the body. This condition becomes unstable if the flow is perturbed or the Reynolds number exceeds 47, then eddies will begin to shed from the body with a harmonic pattern. The development of instabilities results in an unsteady separation equivalent to an oscillating force on the body. If the Reynolds number is low enough (47–400), the laminar vortex shedding known as Karman vortex shedding occurs. These oscillatory vortices arise many challenges in engineering ranging from tall and off-shore structures to tube bundle heat exchangers. Hence, in order to prevent structural damage or maximizing system efficiency, it is mandatory to study and control the behavior of the flow in these situations (Anderson, 2010; Eckert, 2007). The majority of the past research papers on the flow passing bluff bodies were conducted using a two-dimensional circular cylinder. As noted by Roshko (1993) the circular cylinder is, by far, the ‘‘quintessential’’ bluff body. Experiments and researches done by Roshko (1954b), Miller and Williamson (1994); Williamson (1989, 1996); Williamson and Roshko (1990); Williamson and Govardhan (2004), Rockwell (1987) and Kovasznay (1949) underlie further investigations of bluff body wake and vortex shedding. Braza et al. (1986) numerically simulated the wake behind a circular cylinder at Reynolds numbers 100, 200, and 1000 and reported the flow data. In another Numerical research, Park et al. (1998) simulated vortex shedding of a two-dimensional * Corresponding author. E-mail address: kjavadi@sharif.edu (K. Javadi). https://doi.org/10.1016/j.jfluidstructs.2018.06.010 0889-9746/© 2018 Elsevier Ltd. All rights reserved.