Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

Yasir Al-Okbi,Oksana Stalnov,Tze Pei Chong

doi:10.3390/app11062593

Yasir Al-Okbi, Oksana Stalnov + Show 1 more

Open Access

https://doi.org/10.3390/app11062593

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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.

Highlights

Today the aviation industry is facing major challenges with respect to the noise pollution
If we focus on the aerodynamic performances, Fish and Battle [7] show that the humpback whale benefits from tubercles along the leading edge of its flippers, which would resemble remarkably well with the serrated leading edge of owls
By examining the Sound Pressure Level SPL as a function of non-dimensional frequency f ‘ (=fC/U, where C is the aerofoil chord length) generated by the baseline aerofoil in Figure 7a, the mostly broadband nature of the spectrum at the low to medium frequency is related to the turbulence–leading edge interaction noise

Summary

Introduction

Today the aviation industry is facing major challenges with respect to the noise pollution. Narayanan 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. The brief literature review above concerns exclusively the aerofoil with serrated leading edge acting as a simple and effective passive control device for the reduction of interaction broadband noise and mitigation of the boundary layer separation. Leading edge blowing is an attractive method to achieve this objective because the injection of mass flow from the leading edge against the turbulent inflow could potentially decrease the turbulence intensity, the level of interaction noise radiation Another hypothesis is that the interaction between the leading edge jet and the freestream inflow can create a Kelvin–Helmholtz type of shear mechanism to generate vortical structures propagating in the downstream direction along the aerofoil surface.

Aerodynamic Forces

Acoustic Results

Aerodynamic Results