Numerical Simulation And Experiment Study Of The Noise Radiated By Two Circular Cylinders In Tandem Arrangements

The problem of aeroacoustic sound generated by flowing around bluff bodies is extensively occurring in a number of engineering applications, such as navigation industry, offshore platforms, wind engineering and so on. Vortex-shedding from body surface produces a fluctuating lift force which is normal to the flow direction, and can cause structural vibration and noise, even can cause structural damage. So, how to eliminate or reduce acoustic noise has become a serious problem when conducting an engineering or design. To solve it, many researchers have carried on plenty of relative work. In contrast to single circular cylinder, the phenomena of flowing around two circular cylinders in tandem arrangements is more complex and more common due to coupling action between two circular cylinders. Thus conducting researches on the aeroacoustic sound induced by flowing around two circular cylinders in tandem arrangements is of important academic and practical significance.The flow mechanism and radiated noise by a low-speed turbulent flow over two circular cylinders in tandem arrangements has been investigated computationally. After acquired the flow field data which is obtained by using Large Eddy Simulation, hybrid method that couples numerical flow computations with an implementation of the Ffowcs Williams-Hawkings equation is used to capture the flow induced noise. Hybrid method, which split the computational domain into a source region and a propagation region, can separate different length scales, and reduce computational demanding. In order to investigate the influence of circular cylinder diameter, different circular cylinder diameters (such as 5mm, 10mm, 20mm)are used for the two circular cylinders when L/D=2(where L is center distance between two circular cylinder, D is circular cylinder diameter) and incoming flow velocity is 20m/s. And to examine the influence of incoming flow velocity, different flow speeds (such as 10m/s, 20m/s, 50m/s) are employed for the two circular cylinders when L/D=2 and D=10mm. And different spacing ratios (such as L/D=1.5, L/D=2, L/D=3, L/D=5) are also used to investigate the influence of two circular cylinder configurations while the velocity of incoming flow is 20m/s and D=10mm.The results show that the vortex-shedding frequency will reduce and the sound pressure level (SPL) increase when enlarge the circular cylinder diameter. And both the vortex-shedding frequency and the sound pressure level will increase while raise the incoming flow velocity. Different spacing ratios have affected the vortices shedding at a certain extent, also affect the acoustic noise. There is the largest SPL near the critical spacing. And the direction of acoustic fields is obvious.The reduction of acoustic noise induced by flowing around two circular cylinders in tandem arrangements is also discussed in this article. The experiment is conducted in wind tunnel and the result is shown good agreement with numerical simulation.