Trailing edge flows and aerodynamic sound

This paper discusses the theory of the generation of sound by turbulent flow over a trailing-edge flap of an airfoil or guidevane. A narrow slot separates the flap from the airfoil, and the configuration is modelled analytically by a semi-infinite rigid plate that contains a slot at an arbitrary, finite distance from the edge. The aerodynamic sound problem is formulated in terms of a singular integral equation which can be solved in closed form when the width of the slot is small compared with both the acoustic wavelength and the chord of the flap. The theory is applied to examine (i) the influence of the slot on the noise generated as a result of boundary-layer separation close to the trailing edge of the flap, and (ii) the generation of sound by boundary-layer turbulence in the immediate vicinity of the slot. At low, subsonic mean flow Mach numbers the presence of the slot is shown to reduce the level of the radiated noise in case (i) provided that kd < 10, where k is the characteristic acoustic wavenumber and is the chord of the flap. Boundary-layer noise is predicted to be significantly enhanced by the slot in the range 0.1 < kd 10.

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Prediction of Broadband Noise from Symmetric and Cambered Airfoils

INCAS BULLETIN ◽

10.13111/2066-8201.2019.11.1.3 ◽

2019 ◽

Vol 11 (1) ◽

pp. 39-51 ◽

Cited By ~ 2

Author(s):

Vasishta BHARGAVA

Keyword(s):

Mach Number ◽

Sound Pressure ◽

Power Level ◽

Broadband Noise ◽

Chord Length ◽

Trailing Edge ◽

Aerodynamic Sound ◽

Displacement Thickness ◽

Sound Pressure Levels ◽

Naca 0012

Aerodynamic sound generation and self-noise mechanisms from lifting surfaces such as airfoil involve the fields of classical acoustics and fluid mechanics. In this paper, trailing edge noise production is evaluated using empirical model for NACA 0012 and NACA 6320 airfoils. The sound pressure levels from trailing edge surface are calculated for different flow configurations. The growth of boundary layer thickness and displacement thickness, for different chord lengths and Mach numbers with varying angles of attack, is illustrated for NACA 0012. The sound pressure levels were computed numerically between 00 to 60 angles of attack and at constant chord length of 1.2m using Brookes Pope Marcolini method. The results showed a change of ~2-5dB in peak amplitude for mid frequencies region of spectrum. The effects of varying chord length and Mach number on sound pressure levels are illustrated for both airfoils. The relative velocity field for airfoils was computed using the boundary element method. The combined effect of thickness and camber on sound power level is demonstrated at a 40 angle of attack and for a Mach number of 0.191. Validation of sound pressure levels is done based on the results obtained for NACA0012 for similar flow conditions.

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Experimental Investigation of Flow Field Around An Asymmetric Beveled Trailing Edge and Aerodynamic Sound

23rd AIAA/CEAS Aeroacoustics Conference ◽

10.2514/6.2017-3501 ◽

2017 ◽

Author(s):

Yaoyi Guan ◽

Scott C. Morris

Keyword(s):

Experimental Investigation ◽

Flow Field ◽

Trailing Edge ◽

Aerodynamic Sound ◽

Beveled Trailing Edge

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On the added mass of a perforated shell, with application to the generation of aerodynamic sound by a perforated trailing edge

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1979.0014 ◽

1979 ◽

Vol 365 (1721) ◽

pp. 209-233 ◽

Cited By ~ 30

Keyword(s):

Oscillatory Flow ◽

Added Mass ◽

Radius Of Curvature ◽

Trailing Edge ◽

Trailing Edge Noise ◽

Aerodynamic Sound ◽

Solvable In Closed Form ◽

Flow Through ◽

Rigid Shell ◽

Perforated Shell

This paper examines the theory of oscillatory flow through the perforated surface of a rigid shell. The Reynolds number based on the diameter of a typical perforation is sufficiently large that the flow may be assumed to be irrotational. The case in which the surface apertures are small on a scale of the local radius of curvature of the shell is discussed in detail, and a pair of integral equations is derived whose solutions determine the principal properties of the flow, and in particular the fluctuating inertial drag experienced by the shell. These equations are solvable in closed form only for relatively simple shell geometries. Application of the theory is made to the case of a spherical shell, and to the problem of sound generation by turbulence swept past the trailing edge of a perforated aerofoil. Numerical results are presented which support the view that significant reductions in the level of trailing edge noise are possible, and illustrate the dependence of the attenuation on the distribution of perforations.

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