Analysis of noise reduction characteristics of the diffuser surface roughness on interferometric images

2018 ◽  
Author(s):  
Jiaying Zhang ◽  
Wang Hongjun ◽  
Zhu Xueliang ◽  
Liu Bingcai ◽  
Tian Ailing
Keyword(s):  
Surface Roughness ◽  
Noise Reduction ◽  
Reduction Characteristics

scholarly journals Analysis of the Noise Reduction Characteristics of a Diffuser with Fizeau Interferometry

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Hongjun Wang ◽  
Xueliang Zhu ◽  
Bingcai Liu ◽  
Ailing Tian
Keyword(s):  
Surface Roughness ◽  
Noise Reduction ◽  
Rotation Speed ◽  
Effective Range ◽  
Coherent Noise ◽  
Fringe Contrast ◽  
Effective Roughness ◽  
Reduction Characteristics ◽  
The Relationship ◽  
Interference Image

To solve the coherent noise problem of an interference image, the method of a rotating diffuser was adopted to change the coherence of a beam to reduce the noise of the interference system. The relationship between the speed of the diffuser and the signal-to-noise ratio (SNR) of the fringe contrast system was simulated to obtain the diffuser control parameters needed for the best interference fringe state. The fringe contrast of each image and the SNR of the system were analyzed. The results showed that the increased speed of the diffuser reduced the contrast of the interference image to a certain extent, but the increased speed also effectively improved the SNR and facilitated the subsequent interference image processing. Due to the coherent noise in the interferometric system, the method of the rotated diffuser reduced the coherence of the light beam to suppress the noise of the interference image. By analyzing the coherent noise reduction characteristics of the rotated diffuser with different surface roughnesses, the relationship between the surface roughness and the noise contrast for different rotation speeds was simulated, and the effective roughness range with the noise reduction effect was selected. A noise reduction system was built based on Fizeau interference, and the noise contrast of the interference image was collected and calculated. The effective range of σh/λ was 0.2–0.5 when the rotation speed was 10 r/s, while the effective range of σh/λ was 0.4–0.6 when the rotation speed was 100 r/s. The experimental results showed that the surface roughness and wavelength ratio σh/λ of the rotated diffuser increased when the noise contrast tended toward 1, but the effective range of the surface roughness decreased with the increase of the rotational speed of the diffuser.

On the reductions of aerofoil-turbulence interaction noise through multi-wavelength leading edge serrations

2020 ◽  
pp. 095441002096574
Author(s):  
S Narayanan ◽  
Sushil Kumar Singh
Keyword(s):  
Noise Reduction ◽  
Maximum Amplitude ◽  
Leading Edge ◽  
Emission Angle ◽  
Broadband Noise ◽  
Dual Wavelength ◽  
Flat Plates ◽  
Wide Range ◽  
Multi Wavelength ◽  
Reduction Characteristics

This paper provides an experimental study into the use of multi-wavelength sinusoidal leading edge ( LE) serrations for enhancing the aerofoil-broadband noise reductions. The noise reduction performances of multi-wavelength serration profiles introduced on a flat plate are compared against those generated by single-wavelength profiles when applied separately. The multi-wavelength leading edge serration is made in such a way that its maximum amplitude is kept same as that of each single-wavelength ones to be compared. The present study reveals that the dual-wavelength serrations provide higher noise reductions over a narrow band of frequencies as compared to single and triple wavelength ones. Further, it reveals that the noise reduction characteristics of dual-wavelength serrated airfoils are similar to the flat plates. It shows that the baseline plate generate higher noise radiations for all emission angles as compared to leading edge serrated plates, but the common feature among them is the downstream directivity. For the range of frequencies 0.9 to 5 kHz, the highest directivity is seen at an emission angle of 55° for the baseline, while it occurs at 75° for the serrated plates. The dual wavelength serrations generate lowest acoustic radiations as compared to single and triple ones for all the emission angles. Also, it is noticed that the radiation levels of the dual serrations decrease with increase in amplitude of the serration, which shows that the longer dual serrations generate lowest acoustic radiations. Thus, the present study illustrates that the dual wavelength leading edge serrations act as the best passively modified serration profiles for achieving the highest noise reductions over a wide range of frequencies as compared to single and triple wavelength ones.

401 Noise Reduction Characteristics of Noise Canceling in a Sound Field Environment

2014 ◽  
Vol 2014.63 (0) ◽  
pp. _401-1_-_401-2_
Author(s):  
Kazutaka ASAMOTO ◽  
Isao ITO ◽  
Takumi HATAOKA ◽  
Katumi MORIWAKI
Keyword(s):  
Noise Reduction ◽  
Sound Field ◽  
Field Environment ◽  
Reduction Characteristics ◽  
Noise Canceling
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