# Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil +
###### Abstract  
Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence-leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence-leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively. 1  
[PERSON]; [PERSON]; [PERSON] [PERSON] Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil. 1  
[PERSON]; [PERSON]; [PERSON] Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil. 10 March 2021  
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where \(\omega\) is the angular frequency, \(\Lambda_{uu}\) is the longitudinal integral length scale of the turbulence, \(\Gamma\) is the gamma function, \(Tu\) is the turbulence intensity, \(U\) is the velocity, \(R\) is the observer distance, \(S\) is the aerofoil span, \(d\) is the aerofoil thickness, and \(\hat{k}_{\mathrm{x}}^{2}\) is the normalised longitudinal wavenumber. From this expression, apart from the aerofoil geometry and physical configuration, the level of the interaction noise can be governed by the external factors in flow such as the longitudinal turbulence length scale and the turbulence intensity. Inspired by the ability of owl to hunt in acoustic stealth, there is now a great interest to reproduce the shape of owl's wings in aerofoil blades. First, primary feathers on the owls' wing (leading edge) are serrated. Second, the trailing edge feathers of the owl's wing are tattered. Third, the rest of the owls' wing are covered in velvety feathers. It is believed that the leading edge serrations are responsible for the reduction of the leading edge noise. When the leading edge of an aerofoil blade is serrated, it can affect the acoustical response with the incoming turbulent flow. Many studies have already been performed on the effect of leading edge serrations on broadband noise. In a joint experimental-numerical investigation by [PERSON] et al. [2] on the leading edge interaction noise of a NACA 65(12)-10 aerofoil, the wavy leading edge is found to achieve noise reduction between 3-4 dB. [PERSON] et al. [3] performed a fundamental study to assess the effects of a serrated leading edge on the interaction noise characteristics of a flat plate and an aerofoil. A nearly isotropic turbulence was produced using mesh grid positioned inside a nozzle. The authors demonstrate significant noise reduction between 5-8 dB in a flat plate configuration.