Acoustic radiation from an airfoil in a turbulent stream

Noise due to turbulent flow past a trailing edge

A prediction method is developed for the self-generated noise of an airfoil blade encountering smooth flow. The prediction methods for the individual self-noise mechanisms are semiempirical and are based on previous theoretical studies and data obtained from tests of two- and three-dimensional airfoil blade sections. The self-noise mechanisms are due to specific boundary-layer phenomena, that is, the boundary-layer turbulence passing the trailing edge, separated-boundary-layer and stalled flow over an airfoil, vortex shedding due to laminar boundary layer instabilities, vortex shedding from blunt trailing edges, and the turbulent vortex flow existing near the tip of lifting blades. The predictions are compared successfully with published data from three self-noise studies of different airfoil shapes. An application of the prediction method is reported for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements. A computer code of the method is given.

/pdf/airfoil-self-noise-and-prediction-i86qw26cw9.pdf

Airfoil self-noise and prediction

https://ntrs.nasa.gov/api/citations/19780018938/downloads/19780018938.pdf

A review of the theory of trailing edge noise

https://www.cs.odu.edu/~mln/ltrs-pdfs/NASA-2003-pas-ksb.pdf

Modeling aerodynamically generated sound of helicopter rotors

A large parameter solution procedure of Schwartzschild and Landahl is adapted to the task of calculating closed-form approximate solutions for the pressure and lift of a flat-plate, infinite-span airfoil. Two general cases are treated: 1) the two-dimensional subsonic flow problem, in which the large parameter is the upwash frequency, and 2) the three-dimensional incompressible flow problem, in which the large parameter is the spanwise wavenumber of the upwash. For the first case, the four problems of a gust drifting with the freestream, a gust moving at other than the freestream velocity, a plunging motion, and a linear upwash are treated. For the second case, the two problems of a gust drifting with the freestream and a generalized gust moving at other than the freestream velocity are considered. Comparison of the solutions with available numerical results generally shows good agreement when the appropriate parameter is large. The solutions for the gust convecting with the freestream for both the two-dimensional compressible and the three-dimensional incompressible cases were derived previously by Adamczyk using the Wiener-Hopf technique.

High frequency thin-airfoil theory for subsonic flow

Effect of the incident surface pressure field on noise due to turbulent flow past a trailing edge

A theoretical and experimental investigation of the nosie and unsteady surface pressure characteristics of an isolated airfoil in a uniform mean velocity, homogeneous, nearly isotropic turbulence field was conducted. Experiments were performed with a 23-cm chord, two-dimensional, NACA 0012 airfoil in the UTRC Acoustic Research Tunnel over a Mach number range of 0.1 to 0.5. Far-field noise spectra and directivity as well as surface pressure spectra and cross-spectra were obtained. Incident turbulence statistics were documented. Theory applied to predict far-field noise and surface pressure characteristics from measured inflow turbulence statistics showed good agreement with measurement over the dominant frequency range for all Mach numbers investigated. The theoretical formulation represents a first-principles solution providing absolute level prediction without recourse to empirical or adjustable constants. It takes into account compressibility as well as source noncompactness effects. Correlation measurements demonstrated that all chordwise portions of the airfoil radiated directly to the far-field, but that the leading edge was the dominant noise producing region. b c c0 d / g kx,ky,kz

R. K. Amiet

Papers

Acoustic radiation from an airfoil in a turbulent stream

Noise due to turbulent flow past a trailing edge

High frequency thin-airfoil theory for subsonic flow

Effect of the incident surface pressure field on noise due to turbulent flow past a trailing edge

Noise and Surface Pressure Response of an Airfoil to Incident Turbulence