Wake Transition in the Flow Around a Circular Cylinder With Dual Parallel Splitter Plates Attached
- Rui Wang (Shanghai Jiao Tong University) | Yan Bao (Shanghai Jiao Tong University) | Dai Zhou (Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration (CISSE)) | Zhaolong Han (Shanghai Jiao Tong University) | Huan Ping (Shanghai Jiao Tong University)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- Instability control, wakes
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- 21 since 2007
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This study numerically investigates the wake control of a circular cylinder by dual splitter plates symmetrically attached at the rear surface, parallel to the flow. The effect of these plates on the wake transition to three-dimensional structures was examined via a Floquet stability analysis. Simulations for attachment angles of 20 and 40 degrees with a constant splitter plate length were carried out with the Reynolds number in the range of 150 to 350. The results show that the splitter plates have a crucial effect on the onset of secondary instabilities. In comparison to an isolated cylinder, two new modes are found, which are referred to as mode A’ and mode B'. Mode A’ is similar to mode A, but with a quite long critical wavelength. Mode B’ shares the same spatiotemporal symmetries with mode B but has a distinct spatial structure. Furthermore, the ordering of occurrence of the unstable modes can be modified for different geometric configurations. The onset characteristics of the transition modes are analyzed and discussed in detail.
Cross-flow over cylindrical objects is one of the fundamental problems of fluid dynamics and also a common phenomenon in industrial applications, such as offshore structures, bridge piers and skyscrapers. However, the flow separation and alternating vortex shedding in the downstream wake could cause significant increases in the mean drag and lift fluctuations. This intense fluctuation may result in serious structural vibrations or damage. Therefore, the effective wake control of cylindrical structures is of fundamental and practical significance. Owing to its simple geometric configuration and easy implementation, the use of splitter plate as a passive control method has been extensively investigated both experimentally and numerically.
Early investigation on the wake control by a splitter plate is mainly by experiments. The pioneering work was conducted by Roshko (1954), and he revealed that the shear layer interaction behind a circular cylinder is inhibited by a splitter plate of length 5D attached to the rear of the cylinder with diameter D, which results in a substantial reduction in the mean drag coefficient. Later, Bearman (1965) showed that showed that’ the Strouhal number gradually increases with the growth of the plate length and hits the peak at a plate length between 1.25 and 1.5 base height, above which the Strouhal number gradually decreases. The wake flow behind the bluff body was classified into five regimes in terms of different wake behaviors. Gerrard (1966) confirmed that it is primarily the width of the gap rather than the position of the trailing edge of the plate that determines the spectacular discontinuity in the Strouhal number and base pressure observed by Roshko (1954). In order to demonstrate the effects of an attached splitter plates in the wake of a circular cylinder with diameter D, Apelt et al. (1973) performed a series of experiments at subcritical Reynolds numbers in the range 104 < Re < 5×104. It was observed that short splitter plates provided a fixed vortices formation point, leading to a reduction of the wake width with increasing plate length. For long splitter plates, the interaction between the separated shear layers is inhibited, resulting in an irregular downstream vortex sheet. Anderson & Szewczyk (1997) experimentally found that the presence of a splitter plate was capable of reducing the level of 3-dimensionality in the formation region by stabilizing the transverse ‘flapping’ of the shear layers.
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