An experimental and numerical study of bluff body

Abstract

An experimental and numerical investigation was performed in order to firstly establish the aerodynamics and aeroacoustics of a landing gear torque link configuration, and secondly to assess the effectiveness of both passive and active flow control as noise attenuation methods. Experimental and numerical data showed that afixing a torque link on to a half cylinder strut resulted in the suppression of vortex shedding in between the torque arms. This resulted in a narrower wake with reduced drag. PIV wake profiles showed the suppression of shedding to result in reduced velocity fluctuations, as shown by reductions in shear and normal Reynolds stresses. Simulation showed attaching the torque link to the strut to result in a reduction of farfield noise levels by up to 7.5 dB. Altering the torque link angle ttheta was shown to affect the aerodynamic field, with a decrease in drag and wake strength, as shown by a reduction in mean and fluctuating velocities. However, altering the torque link angle was shown to have little affect on near field acoustics. Altering the yaw angle φ from φ = 0º to 180º was shown to affect periodic vortex shedding from the strut, with shedding occurring at lower frequencies for φ = 90º and 135º. Phased microphone array data showed interaction between the strut's wake and the downstream torque link to be the major source of noise for yaw angles with the torque link almost or entirely aligned with the strut. This interaction noise decreased when the torque link was out of alignment with the strut. The major source of noise for these yaw angles became edge noise due to the torque link extending into the freestream. Both experimental and numerical acoustics showed φ = 0º and 180º to exhibit the loudest OASPL. A conformal fairing applied over the torque link 'gap region' was found to be effective in attenuating interaction noise. The most effective application of the fairing was found for the standard yaw angle of φ = 0º, with noise reductions of up to 4.5 dB. Active flow control applied in the form of blowing from the landing gear strut was also found to be effective at reducing interaction noise when applied from blowing angles of 30º and 90º. Blowing was found to reduce the strength of the wake and to deflect the wake away from the downstream torque link, resulting in a decrease in tonal noise by up to 10.3 dB and a reduction in broadband noise of up to 6 dB over 0.01 ≤ St ≤ 1.

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