Large eddy simulation and FW-H acoustic analogy method are performed to investigate the effect of serrated leading edge on rod-airfoil interaction (RAI) noise. A NACA 0012 airfoil with straight and serrated leading edge at zero angle of attack is located one chord length behind a cylinder rod. The leading edge serrations are in the form of sinusoidal profiles .The free stream Mach number is 0.2 and the Reynolds number based on the rod diameter is 48,000. Firstly, the numerical results of straight leading edge airfoil are compared with experimental data, both the flow field predictions and the acoustic results are in good agreement with experiment. Secondly, the numerical results are compared between straight and serrated airfoils. The wake of the serrated airfoil is a little bit narrower and weaker and the leading edge serrations efficiently reduce the span-wise correlation coefficient. There is almost no noise reduction effect below the Karman vortex shedding frequency. The reduction of SPL at the Karman vortex shedding frequency is about 2.4 dB. A significant noise reduction is achieved by the serrations over a quite wide frequency range between 2 KHz and 6.5 KHz. It can be noted that the OASPL directivities at different azimuth angles all reduced 2-5.5 dB due to the serrations, which means than the leading serrations are an effective passive flow control method to reduce RAI noise. NomenclatureA = amplitude of the leading edge serration W = wavelength of the leading edge serration c = baseline airfoil chord lenght c(z) = serrated airfoil chord length c = serrated airfoil mean chord length d = cylinder rod diameter L span = span-wise length of the experiment L sim = span-wise length of the simulation R = radius of the observer points around the airfoil a 0 = free stream speed of sound 0  = free stream dendity U 0 = free stream velocity 2 u mean = stream-wise mean velocity RMS = root mean square rms u = root mean square of stream-wise velocity fluctuation rms p = root mean square of pressure fluctuation f 0 = Karman vortex shedding frequency St = Strouhal number C L = lift coefficient of the airfoil C D = drag coefficient of the airfoil C P = pressure coefficient SPL = sound pressure level PWL = sound power level PSD = power spectral density OASPL = overall sound pressure level FFT = fast Fourier transform

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An acoustic experiment is conducted to investigate the noise reduction potential of trailing edge(TE) serrations on SD2030 airfoils in a normal test bed with high interference noise source. The Reynolds number is 3.1×10 5 and the serration geometry λ/h is 0.8. Noise sources located at test region are recognized clearly by use of a microphone array. With the application of serrated TE, trailing edge noise can be reduced efficiently. An average noise reduction of 3.3 dB is obtained. Large-Eddy Simulation and Ffowcs Willams & Hawkings analogy have been used to study noise reduction mechanisms of serrated TE. Serrated TE decreases the airfoil aerodynamic performance significantly. Spiral flows from pressure side to suction side surface have been formed around serrations and the pre-mixing proess influences the boundary layer characteristics on airfoil suction side, such as separation vortices. When ignore the monopole source and quadrupole source terms, spectra of airfoil self-noise are dominated by tones which are strongly related to separation vortices' shedding process. By investigating pressure fluctuation distributions on airfoil surface, the most important noise source regions have been found. Serrated TE significantly decreases the pressure fluctuations correspond to peak frequencies in noise spectra. As a result, tones are reduced up to 16.3 dB. Although noise increases as mentioned by Gruber are found when f δ > 1.27, the overall noise reduction reaches 14 dB. Nomenclature λ = serration wavelength h = amplitude of the serrations L = characteristic length T 60 = reverberation time V = room volume r H = reverberation radius r' = propagation distance of reflect wave r = propagation distance of direct incident wave l = length U c = eddy convection velocity U = mean velocity p = static pressure p' = fluctuation of static pressue δ * = boundary layer displacement thickness θ * = boundary layer momentum thickness f = frequency c = chord of airfoil f δ = strouhal number,

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