Comparing the wake behind circular and elliptical cylinders in a uniform current
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Comparing the wake behind circular and elliptical cylinders in a uniform current Mohammad Javad Ezadi Yazdi1 · Abdulamir Bak Khoshnevis2 Received: 17 July 2019 / Accepted: 4 April 2020 / Published online: 30 April 2020 © Springer Nature Switzerland AG 2020
Abstract In this study, an experimental investigation has been conducted on the characteristics of the wake behind the elliptical cylinder with the axis ratio of AR = 2 . In order to provide a comparison, the same experimental investigation has also been conducted for a circular cylinder with the vertical height equal to the height of the elliptical cylinder. For studying the wake behind these two cylinders, hot-wire anemometry measurement has been performed. All of the tests are carried out in Reynolds number of 3.0 × 104 (which is defined according to the mean velocity of air and the cylinder diameter). Results are presented in terms of time-averaged velocity, standard deviation, higher-order central moments of the hotwire signals (skewness and kurtosis factors), Strouhal number and drag coefficient. For the regions near the wake, the velocity deficit of the elliptical cylinder is greater compared to the circular cylinder; however, this is completely reversed in the regions far from the wake. As the axis ratio of the cylinder decreases, the dimensionless standard deviation becomes higher, and it’s maximum value is located at an earlier stream-wise location. In addition, it is observed that by increasing the axis ratio of the cylinder, drag coefficient decreases, while the Strouhal number is increasing. Keywords Wind tunnel · Hot-wire anemometry · Circular and elliptical cylinders · Drag coefficient · Standard deviation
1 Introduction The cross flow through the cylinders have extensive applications in engineering filed such as cooling towers, heat exchangers, chimney stacks, nuclear reactors, and offshore structures. Consequently, a large number of researches have been conducted on this kind of flow, mainly through circular cylinders. Here, we mention some of them, in which the experimental and numerical methods are applied. This geometrical configuration was firstly investigated experimentally by famous physicists like Strouhal, Von Kármán and Prandtl in late nineteenth and early twentieth century (Refer to Williamson [1] and its references). The transition between laminar and turbulent flow occurs in special flow conditions and geometries, in
other words, it occurs mainly according to the interactions between unstable regions of flow and not due to the geometry of body itself. As can be seen in Fig. 1, the passing flow through cylinders is very complicated. The area around the cylinder can be divided into three main regions, including boundary layer region of the cylinder, the region comprising two shear layers on the top and bottom of the cylinder and finally, the region representing the wake. Several studies such as Bloor [2], Gerrard [3] and Roshko [4, 5] have been conducted for investigating the different regimes the corresponding phenomena in these
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