An Investigation On Tonal Trailing Edge Noise Generation Mechanisms Of The Airfoil For Low To Moderate Reynolds Number

As the small wind turbine(SWT)gains its popularity,its noise issue has come into the public spotlight.Aerodynamic noise is the main acoustic source of the SWT and among them,tonal tailing edge noise is the most concerned.Understanding the generation mechanism is a crutial prerequisite for controlling the airfoil tonal trailing edge noise,therefore research into the airfoil tonal trailing edge noise generation is paramount to addressing the noise issue of SWT.Nowadays,related investigations abound in academic field and previous research all indicate that the tonal trailing edge noise generation is complex,with differing mechanisms under different Reynolds numbers or angles of attack.Despite this,current research all solely focuses on the mechanism of a certain flow condition,lacking a comprehensive and systematic investigation for a whole range of flow conditions.In view of this,this thesis devotes to investigating the tonal trailing edge noise comprehensively from low to moderate Reynolds numbers under different angles of attack and also clarifies some contradictory points in relevant open literatures.Main conclusions in this thesis are as follows:(1)In low Reynolds number conditions,linear instabilities(T-S waves)only exist on the suction side of the airfoil while flow on the pressure side remains rather stable.Tones in the sound spectra are only related to the T-S waves on the suction side.At this Reynolds number,feedback mechanism is not established between the T-S waves and acoustic waves,therefore only a single tone and its harmonices exist in the sound spectra.(2)In moderate Reynolds number conditions,T-S waves exist on both side of the airfoil.Two humps in the sound dpectra is associated with T-S waves on each side of the airfoil respectively.At this Reynolds number,a feedback mechanism is established between T-S waves and acoustic waves on both sides of the airfoil,therefore multiple tones exist in each hump in the sound spectra.(3)Compared with Reynolds number,angle of attack has a much less pronounced influence on the generation mechanism of the tonal trailing edge noise,which is typically manifested by the heightening of linear instabilities on suction side and weakening of linear instabilities on pressure side.