Abstract
This paper presents the results of an experimental study into the effect of add-on type leading edge serrations on the aeroacoustic and aerodynamic performances of a symmetrical NACA0008 aerofoil. The aeroacoustic part of this paper studies the reduction of interaction broadband noise in the presence of elevated freestream turbulence by employing serrated leading edges. For non-dimensional frequencies f′ < 1, the resulting sound pressure level reduction (ΔSPL) was found to be a linear function of f′ and the ΔSPL depends only on the serration amplitude, serration wavelength and freestream velocity. Leading edge with a large serration amplitude was found to be very effective in the reduction of broadband noise where up to ΔSPL ≈ 8 dB is achievable. It is generally more beneficial to choose a leading edge with a smaller serration wavelength, although the most effective configuration actually combines the largest serration amplitude and the largest serration wavelength. Interestingly, for a curved-serration, the most optimised configuration (with small serration wavelength, large serration amplitude, small inclination angle and large curvature radius) was found to outperform its straight-serration counterpart by a further 5 dB reduction of broadband noise at the same frequency. Concerning the aerodynamic part of the study, to effectively suppress boundary layer stall without incurring severe drag penalties for low freestream turbulence intensity, the most effective leading edge serration should possess a large serration wavelength and small serration amplitude. Hence, the serration geometry that works very well for a low noise aerofoil is usually inferior in the aerodynamic performance, and vice versa. The best compromise for the serration geometry that can still harness good performances in both the aeroacoustic and aerodynamic should possess the largest serration amplitude and the largest serration wavelength. This paper demonstrates that, when optimised properly, the add-on type leading edge serration can be very effective in both the reduction of the interaction broadband noise, and the suppression of the boundary layer separation at high angle of attack.
Highlights
It has been shown that noise generated by many industrial operations produces considerable negative impact on the environment, which has become an increasingly sensitive topic
The first objective of this paper is to address whether an add-on serrated leading edge can produce a similar level of interaction broadband noise reduction typically achieved by those of the cut-in type
This paper presents experimental results of the effect of add-on type leading edge serrations on the aeroacoustic and aerodynamic performances of a symmetrical NACA0008 aerofoil
Summary
It has been shown that noise generated by many industrial operations produces considerable negative impact on the environment, which has become an increasingly sensitive topic. Chong / Journal of Sound and Vibration 425 (2018) 324e343 contributor to the noise pollution levels on a global scale As a result, it is receiving significant attention in terms of its impact on the communities surrounding the large airports. The ACARE Flightpath 2050 initiative aims to achieve a 65% reduction in commercial aviation noise emissions by 2050, relative to the level in the year 2000. The focus has shifted to the development of advanced and efficient aero-engines that produce smaller carbon footprints and noise radiation levels. Other aircraft noise sources (e.g. airframe noise, fan noise and combustion noise) become increasingly important
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