Laminar flow instabilities of a grooved circular cylinder
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(2020) 42:580
TECHNICAL PAPER
Laminar flow instabilities of a grooved circular cylinder Javad Farrokhi Derakhshandeh1 · Nima Gharib1 Received: 23 April 2020 / Accepted: 1 October 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020
Abstract This paper represents a numerical study on the flow past a grooved circular cylinder with a diameter of D. The study aims to investigate the instabilities of the flow at laminar flow regimes when Reynolds number varies from 50 to 200. Three different geometrical grooves are examined, including square, triangular, and dimple. The grooves are located at 𝜃 = 0°, 30°, 45°, 60° and 90°, separately relative to the front stagnation point. The effects of the groove on the flow control and imposed forces on the cylinder are studied at different Re. It is found that the presence of the groove affects the dynamic behaviour of the streamwise vortices. This behaviour leads to alteration of the pressure coefficient and a significant increment in lift coefficient, in particular for the triangular grooved cylinder. At Re = 200, the results show that the magnitude of the lift coefficient of the triangular grooved cylinder with 𝜃 = 45° is 200% more than that of the square grooved cylinder. The results also reveal that the drag coefficient reduces up to 100% by employing a triangular groove shape at 𝜃 = 45°. These variation in lift and drag coefficients leads to maximising the aerodynamic efficiency factor (lift-to-drag ratio) of the triangular grooved cylinder up to 200%. Keywords Laminar flow · Grooved circular cylinder · Vortex shedding · Wake structure · Lift-to-drag ratio
1 Introduction This paper focuses on a 2D laminar flow over a grooved circular cylinder. Flow passing a circular cylinder has been extensively studied in the literature due to the importance of its application such as flow around towers, offshore structures, and heat exchangers. Flow past circular cylinders has received excellent attention in the literature in both laminar and turbulent flow regimes [4, 6, 24, 25, 30, 36, 38, 39, 44, 46, 48–50]. In a laminar viscous flow with relatively low Reynolds numbers, creeping and steady separated and periodic laminar wake flow regimes can occur [16, 17, 27, 41, 50]. Here, the Reynolds number is defined as Re = UD∕𝜗 , where U is the free stream velocity of the fluid, D stands for the hydraulic diameter of the cylinder, which is identical with the diameter of the cylinder, and 𝜗 represents the kinematic viscosity of
Technical Editor: Jader Barbosa. * Javad Farrokhi Derakhshandeh [email protected] 1
College of Engineering and Technology, American University of the Middle East, Kuwait, Kuwait
the fluid. Though the smooth circular cylinder is known as a most straightforward cross-section geometry [5, 18], the wake structure of the circular cylinder is affected by a few parameters such as Re, aspect ratio of the cylinder, blockage ratio, dimples, and surface roughness [7, 13, 25]. It was shown that the surface roughness also significantly affects th
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