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Wind and Structures
  Volume 23, Number 2, August 2016, pages 109-125

Flow interference between two tripped cylinders
Md. Mahbub Alam, Sangil Kim and Dilip Kumar Maiti

    Flow interference is investigated between two tripped cylinders of identical diameter D at stagger angle = 0 ~ 180 and gap spacing ratio P* (= P/D) = 0.1 ~ 5, where a is the angle between the freestream velocity and the line connecting the cylinder centers, and P is the gap width between the cylinders. Two tripwires, each of diameter 0.1D, were attached on each cylinder at azimuthal angle b= +-30, respectively. Time-mean drag coefficient (CD) and fluctuating drag (CDf) and lift (CLf) coefficients on the two tripped cylinders were measured and compared with those on plain cylinders. We also conducted surface pressure measurements to assimilate the fluid dynamics around the cylinders. CD, CDf and CLf all for the plain cylinders are strong function of a and P* due to strong mutual interference between the cylinders, connected to six interactions (Alam and Meyer 2011), namely boundary layer and cylinder, shear-layer/wake and cylinder, shear layer and shear layer, vortex and cylinder, vortex and shear layer, and vortex and vortex interactions. CD, CDf and CLf are very large for vortex and cylinder, vortex and shear layer, and vortex and vortex interactions, i.e., the interactions where vortex is involved. On the other hand, the interference as well as the strong interactions involving vortices is suppressed for the tripped cylinders, resulting in insignificant variations in CD, CDf and CLf with a and P*. In most of the (a, P* ) region, the suppressions in CD, CDf and CLf are about 58%, 65% and 85%, respectively, with maximum suppressions 60%, 80% and 90%.
Key Words
    interactions; aerodynamics; two cylinders; tripped cylinders; trip wires; wake; forces; vortex; shear layer; staggered arrangement
Md. Mahbub Alam: Institute for Turbulence-Noise-Vibration Interaction and Control, Shenzhen Graduate School,
Harbin Institute of Technology, Shenzhen 518055, China;
Digital Engineering Laboratory of Offshore Equipment, Shenzhen, China
Sangil Kim : Department of Mechanical Engineering, Kangwon National University, 346 Jungang-ro, Samcheok 25913, Republic of Korea
Kumar Maiti: Department of Applied Mathematics with Oceanology and Computer Programming, Vidyasagar University, Midnapur WB, India

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