Why Do the Acoustics and the Dynamics of a Hypothetical Mean Flow Bear on the Issue of Sound Generation by Turbulence?

Sound Generation of a Turbine Stage Due to Non-uniform Mean Flow Temperatures

16th AIAA/CEAS Aeroacoustics Conference ◽

10.2514/6.2010-3977 ◽

2010 ◽

Author(s):

Zhongqiang Mu ◽

Ulf Michel ◽

Mathias Steger ◽

Graham Ashcroft ◽

Fritz Kennepohl ◽

...

Keyword(s):

Sound Generation ◽

Turbine Stage ◽

Mean Flow

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Computation of the bluff-body sound generation by a self-consistent mean flow formulation

Physics of Fluids ◽

10.1063/1.4997536 ◽

2018 ◽

Vol 30 (3) ◽

pp. 036102 ◽

Cited By ~ 9

Author(s):

A. Fani ◽

V. Citro ◽

F. Giannetti ◽

F. Auteri

Keyword(s):

Bluff Body ◽

Sound Generation ◽

Mean Flow ◽

Self Consistent

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On sound generation by the interaction between turbulence and a cascade of airfoils with non-uniform mean flow

Journal of Fluid Mechanics ◽

10.1017/s0022112002008698 ◽

2002 ◽

Vol 463 ◽

pp. 25-52 ◽

Cited By ~ 77

Author(s):

I. EVERS ◽

N. PEAKE

Keyword(s):

Flat Plate ◽

Steady Flow ◽

Power Level ◽

Angle Of Attack ◽

Leading Edge ◽

Sound Generation ◽

Mean Flow ◽

Noise Levels ◽

Flat Plates ◽

Blade Geometry

The sound generated by the interaction between a turbulent rotor wake and a stator is modelled by considering the gust response of a cascade of blades in non-uniform, subsonic mean flow. Previous work by Hanson & Horan (1998) that considers a cascade of flat plates at zero incidence is extended to take into account blade geometry and angle of attack. Our approach is based on the work of Peake & Kerschen (1997), who calculate the forward radiation due to the interaction between a single vortical gust and a cascade of flat plates at non-zero angle of attack. The extensions completed in this present paper are two-fold: first we include the effects of small but non-zero camber and thickness; and second we produce uniformly valid approximations which predict the upstream radiation near modal cut-off. The thin-airfoil singularity in the steady flow at each leading edge is crucial in our model of the sound generation. A new analytical expression for the coefficient of this singularity is derived via a sequence of conformal mappings, and it turns out that in our asymptotic limit this is the only quantity which needs to be calculated from the steady flow in order to predict time-averaged noise levels. Once the response to a single gust has been completed, we use Hanson & Horan (1998)'s approach to determine the response to an incident turbulent spectrum, and find that as well as the noise corresponding to the auto-correlation of the gust velocity component normal to the blade, there is also a contribution from the cross-correlation of the normal and tangential velocities. Predictions are made of the effects of blade geometry on the upstream acoustic power level. The blade geometry can have a very significant effect on the noise generated by interaction with a single gust, with changes of up to 10 dB from the flat-plate noise levels. However, once these gust results have been integrated over a full incident turbulence spectrum the effects of the geometry are rather smaller, although still potentially significant, leading to changes of up to about 2 dB from the flat-plate results. The implication of all this is that the blade geometry can have a significant effect on the tonal noise components generated by rotor–stator interaction (i.e. by single harmonic gusts), but that the broadband part of the noise spectrum is relatively unaffected.

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Influence of incidence angle on sound generation by airfoils interacting with high-frequency gusts

Journal of Fluid Mechanics ◽

10.1017/s0022112095001522 ◽

1995 ◽

Vol 292 ◽

pp. 271-304 ◽

Cited By ~ 55

Author(s):

Matthew R. Myers ◽

E. J. Kerschen

Keyword(s):

High Frequency ◽

Incidence Angle ◽

Outer Region ◽

Sound Field ◽

Leading Edge ◽

Edge Region ◽

Sound Generation ◽

Mean Flow ◽

Flow Stagnation ◽

Trailing Edges

A theoretical model is developed for the sound generated when a convected vortical or entropic gust encounters an airfoil at non-zero angle of attack. The theory is based on a linearization of the Euler equations about the steady subsonic flow past the airfoil. High-frequency gusts, whose wavelengths are short compared to the airfoil chord, but long compared to the displacement of the mean-flow stagnation point from the leading edge, are considered. The analysis utilizes singular-perturbation techniques and involves four asymptotic regions. Local regions, which scale on the gust wavelength, are present at the airfoil leading and trailing edges. Behind the airfoil a ‘transition’ region, which is similar to the transition zone between illuminated and shadow zones in optical problems, is present. In the outer region, far away from the airfoil edges and wake, the solution has a geometric-acoustics form. The primary sound generation is found to be concentrated in the local leading-edge region. The trailing edge plays a secondary role as a scatterer of the sound generated in the leading-edge region. Parametric calculations are presented which illustrate that moderate levels of airfoil steady loading can significantly affect the sound field produced by airfoil–gust interactions.

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Mean Flow Effects on the Low-Wavenumber Pressure Spectrum on a Flexible Surface

Journal of Fluids Engineering ◽

10.1115/1.3242527 ◽

1986 ◽

Vol 108 (1) ◽

pp. 104-108 ◽

Cited By ~ 9

Author(s):

A. P. Dowling

Keyword(s):

Boundary Layer ◽

Coating Layer ◽

Flow Profile ◽

Sound Generation ◽

Rigid Surface ◽

Mean Flow ◽

Flow Noise ◽

Flexible Surface ◽

The Mean ◽

Flow Effects

The Lighthill theory is extended so that it may be used to determine the flow noise induced by a turbulent boundary layer over a plane homogeneous flexible surface. The influence of the surface properties and the mean flow on the sound generation is brought out explicitly through the use of a Green function. The form of the low-wavenumber wall-pressure spectrum on a rigid surface with an arbitrary mean flow profile is determined. The effect of a coating layer is investigated.

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SOUND GENERATION BY ONE-CELL AND TWO-CELL VORTICES IN A NONUNIFORM FLOW

Journal of Computational Acoustics ◽

10.1142/s0218396x06003074 ◽

2006 ◽

Vol 14 (03) ◽

pp. 321-337 ◽

Cited By ~ 1

Author(s):

TING-HUI ZHENG ◽

GEORGIOS H. VATISTAS ◽

ALEX POVITSKY

Keyword(s):

Mach Number ◽

Acoustic Wave ◽

Boundary Conditions ◽

Radial Velocity ◽

Acoustic Pressure ◽

Tangential Velocity ◽

Maximum Amplitude ◽

Vortical Flow ◽

Sound Generation ◽

Mean Flow

Sound generation by vortical disturbance in a subsonic flow around a cylinder is investigated, using different vortex formulations, by solving both linearized and nonlinear Euler equations numerically. Numerical errors associated with the finite-difference discretization and boundary conditions are kept small using the high-order-accurate spatial differentiation and time marching schemes along with accurate nonreflecting boundary conditions and the sponge layer. If the radial velocity in vortex is assumed equal to zero, the intensity and directivity of acoustic wave patterns appear to be quite similar for all vortex models. If the radial velocity is taken into consideration, for single-cell vortex, there is no noticeable change happening to the acoustic wave; for two-cell vortex, although the radial velocity is still much smaller than the tangential velocity, the former plays an important role in generation and propagation of nonsymmetrical sound waves. If only initial tangential velocity or only initial radial velocity of the two-cell vortical flow disturbance is considered, the generated sound level would increase with the Mach number of mean flow while the angular distribution of sound directivity remains the same. If the two-cell vortex with both velocity components is considered, the Mach number of the background flow would change not only the amplitude of the acoustic pressure but also the directivity of sound. As the Mach number increases, the maximum amplitude of acoustic pressure will be shifted to the upper half-plane.

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