Noise Control by a Rotating Rod in a Rod-Airfoil Configuration

In the present paper, a rotating cylinder is investigated as a noise reduction technique in the rod-airfoil canonical benchmark. Noise prediction is realized by a 2D hybrid computational aeroacoustics approach. Rotation is introduced to the cylinder at rotational frequencies ranging from 1/32 to 2 times the shedding frequency of the nonrotating case. Evaluation of all test cases proves that notable noise reduction may be achieved by a cylinder rotating at frequencies greater than the shedding frequency of the nonrotating case. Introduction of rod rotation leads to the generation of positive lift on the rod, which is increased significantly with increasing rotational frequencies. Additional study of the flow field leads to interconnection of noise reduction with the suppression of vortex shedding at high rotational frequencies. The cases that show reduced noise emissions also present gradual suppression of the vortex shedding, which is the main contributor to noise generation. It is also shown that high cylinder rotational frequencies lead to significant increase of the vortex shedding frequency of the rotating cylinder, whereas the shift of the vortex shedding frequency additionally leads to a shift of the dominant tones of the acoustic spectra. The present investigation proves the potential of a rotating cylinder as a noise control mechanism capable of achieving noise reduction in airframe configurations, while additionally enhancing lift generation.