Abstract
This paper concerns the application of a linear microphone array in the quantitative evaluation of blade trailing-edge (TE) noise reduction. The noise radiation from the blades with straight and serrated TEs is measured in an indoor open-jet wind tunnel. The array data are processed using the inverse method based on the Clean algorithm based on spatial source coherence (Clean-SC). In order to obtain correct application and achieve the best effect for the microphone array test, the computing software for array data reduction is firstly developed and assessed by Sarradj’s benchmark case. The assessment results show that the present array data processing method has a good accuracy with an error less than 0.5 dB in a wide frequency range. Then, a linear array with 32 microphones is designed to identify the noise source of a NACA65(12)-10 blade. The performance of the Clean-SC algorithm is compared with the Clean algorithm based on point spread functions (Clean-PSF) method for experimentally identifying the noise sources of the blade. The results show that there is about a 2 dB error when using the Clean-PSF algorithm due to the interference of different aerodynamic noise sources. Experimental studies are conducted to study the blade TE noise reduction using serrated TEs. The TE noise for the blade with and without sawtooth configurations is measured with the flow speeds from 20 m/s to 70 m/s, and the corresponding Reynolds numbers based on the chord are from 200,000 to 700,000. Parametric studies of the sawtooth amplitude and wavelength are conducted to understand the noise reduction law. It is observed that the TE noise reduction is sensitive to both the amplitude and wavelength. The flow speed also affects the noise reduction in the serrated TEs. To obtain the best noise suppression effect, the sawtooth configuration should be carefully designed according to the actual working conditions and airflow parameters.
Highlights
Turbulence broadband noise from the trailing-edge (TE) and leading-edge (LE) of an airfoil/blade is an important and challenging problem in aeroacoustics [1]
The results from other groups are shown in the figure, including Brandenburg University of Technology Cottbus (BTU), University of Adelaide (UniA), PSA3, and Delft University of Technology (TUD) [37]
It could be seen from the beamforming results that the main lobes of LE and TE noise all have some width in space
Summary
Turbulence broadband noise from the trailing-edge (TE) and leading-edge (LE) of an airfoil/blade is an important and challenging problem in aeroacoustics [1]. We use another noise reduction treatment named serrated TEs which have been initially modeled by Howe [26,27]. In order to explore the noise generation mechanism of LE and TE noise, and to assess the noise reduction effect of the noise control treatments, it is necessary to separate and quantify the airfoil LE and TE noise source This is because most of the aerodynamic and performance tests are carried out in the non-anechoic indoor test bed, and not all aeroacoustic tests can be done in a perfect anechoic chamber. This study concerns the quantitative evaluation of the blade TE noise reduction with serrated TEs based on the Clean-SC algorithm. The cross spectral matrix is computed using 1024 data points with a Hanning window and 50% overlap, resulting in a frequency resolution of 50 Hz
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