Wake Manipulation Using Control Cylinders in a Tandem Arrangement
The drag reduction phenomenon of a circular cylinder is investigated, using an X-wire probe, by placing a smaller diameter control cylinder of either circular or square cross-sectional upstream of the main circular cylinder. The separation between the two
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Abstract The drag reduction phenomenon of a circular cylinder is investigated, using an X-wire probe, by placing a smaller diameter control cylinder of either circular or square cross-sectional upstream of the main circular cylinder. The separation between the two cylinders was chosen so as to minimise the overall drag of the main cylinder. Although both configurations resulted in drag reduction, the square control cylinder yielded a bigger reduction and had a greater impact on the mean velocity and turbulent velocity fluctuations in the wake. Both control cylinders led to a reduction in the wake half-width. Spectra in the near wake did not indicate any suppression in vortex shedding. Keywords Wake control
Cylinder wake Tandem
1 Introduction The drag of a circular cylinder and the vortex shedding phenomenon have been extensively investigated because of their importance in aerodynamic flows (Alam et al. 2011; Hu and Zhou 2008). Significant attention is now being focused on controlling the vortex shedding as well as reducing the drag by placing a control cylinder upstream of the main cylinder. The diameter of the control cylinder is generally smaller than that of the main cylinder. However, there have been few systematic investigations of the wake characteristics, such as mean velocity and turbulent velocity rms distributions, downstream of the main cylinder associated with the drag reduction phenomenon. The main aim of the present study is twofold—firstly to investigate the drag reduction phenomenon by placing a small S. Rajagopalan N. Lefeuvre R. A. Antonia L. Djenidi (&) School of Engineering, University of Newcastle, Newcastle, NSW 2308, Australia e-mail: [email protected]
Y. Zhou et al. (eds.), Fluid-Structure-Sound Interactions and Control, Lecture Notes in Mechanical Engineering, DOI: 10.1007/978-3-642-40371-2_23, Springer-Verlag Berlin Heidelberg 2014
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diameter control cylinder upstream of the main cylinder and secondly to compare mean velocity, rms velocity fluctuations, and Reynolds stresses corresponding to the minimum drag configuration at several downstream locations with those for a single cylinder. The influence of the geometry of the control cylinder—e.g., circular, square, triangular and channel cross sections—on the drag reduction, vortex shedding, and wake turbulence characteristics is another objective of the present study although only results for circular and square control cylinders are given here.
2 Experimental Conditions Measurements were made in a 2.2-m-long and 0.34 9 0.34 m test section of a low-speed wind tunnel at a Reynolds number ReD = 7,500 based on the main cylinder diameter D (ReD = U0 D/m where D = 11.1 mm and upstream velocity U0 = 10 m/s). A 3-mm-diameter (d) control cylinder and a 3-mm-diameter square cylinder were used independently in the investigations. The control cylinders were placed upstream of the main cylinder on the centre line, and the separation between the two cylinders was varied by using two micromet
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