Direct simulations of trailing-edge noise generation from two-dimensional airfoils at low Reynolds numbers

Ikeda, Tomoaki; Atobe, Takashi; Takagi, Shohei

doi:10.1016/j.jsv.2011.09.019

Cited by 41 publications

(21 citation statements)

References 37 publications

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“…They also succeeded in suppressing trailing-edge noise using a thin plate attached to the trailing edge of the model, and observed naturally growing T-S waves with broadband characteristics, showing the existence of a feedback loop between unstable T-S waves in the boundary layer and trailing-edge noise. These observations also exhibit good agreement with the analytical results of McAlpine et al The existence of a feedback loop is also supported by several numerical simulations, namely those of Desquesnes et al 14) and Ikeda et al, 15) both of whom further pursued the idea that the most amplified wave is responsible for causing tone generation.…”

Section: Introductionsupporting

confidence: 80%

Frequency Control of Unstable Disturbances in a Two-Dimensional Jet by Means of an Artificial Acoustic Loop

Takagi

Yamaya²,

Itoh

2014

Trans. Japan Soc. Aero. S Sci.

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The frequency of acoustic sound emanating from the trailing edge of a two-dimensional airfoil is known to exhibit a ladder-like variation, displaying discontinuous jumps between discretely identifiable states as the free stream velocity varies. In order to reveal the underlying causes for this behavior, a two-dimensional jet issuing into still air with no aerodynamic sound emission is used as a model platform to study this phenomenon, because prescribed aero-acoustic sound may be readily introduced into the flow at the jet exit. When unstable disturbances growing in the shear layer of the jet are excited by a loudspeaker, an acoustic feedback loop automatically selects one frequency from the unstable frequencies present in the shear layer, and the resulting ladder-like variations are found to be similar to those present in airfoil trailing-edge noise. In addition, the observed slope of each rung of the ladder in the selected frequency behavior, and the observed jump frequency between ladder steps, show good agreement with existing empirical models. It is also discovered that when the remainder of the distance between the speaker and jet divided by the wavelength of the selected acoustic sound is equivalent to one-half wavelength of the accepted sound, the selected frequency jumps to another state.

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Section: Introductionsupporting

confidence: 80%

Frequency Control of Unstable Disturbances in a Two-Dimensional Jet by Means of an Artificial Acoustic Loop

Takagi

Yamaya²,

Itoh

2014

Trans. Japan Soc. Aero. S Sci.

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“…By using Eq. (1), ∆f = 0.42 corresponds to U c 0.47U ∞ , which is a little higher than U c /U ∞ 0.4 reported in [14] and also usually given by a linear stability analysis, but still in a reasonable range; the phase velocity U c 0.5U ∞ was reported in the two-dimensional calculation of NACA0006 airfoil at Re = 20, 000 [17]. The present observation strongly suggests the formation of a feedback loop mechanism.…”

Section: Acoustic Feedback Loop In Three-dimensional Fieldsmentioning

confidence: 57%

“…The transition of vortex shedding patterns due to the onset of an AFL, is well related with the difference of hydrodynamic instability mechanisms between wake and boundary layer [17]. Fig.…”

Section: Time-averaged Aerodynamic Forcesmentioning

confidence: 66%

“…4. The onset of an AFL also lowers the shedding frequency due to the difference of instability mechanisms between the wake and the upper-side boundary layer [17]. In Fig.…”

Section: Unsteadiness Of Two-dimensional Flowmentioning

confidence: 91%

“…They were examined in three dimensions, but resulted in two-dimensional time-periodic states. Since an AFL can be explained with a two-dimensional mechanism [12,17], the two-dimensional unsteady phenomenon can be dominant unless a separated shear layer on suction side becomes sufficiently unstable. The other three airfoils of the NACA4x06 set, all reached self-sustaining, three-dimensional unsteady states at α = 8°.…”

Section: Time-averaged Aerodynamic Forcesmentioning

confidence: 99%

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Self-Noise Effects on Aerodynamics of Cambered Airfoils at Low Reynolds Number

Ikeda¹,

Atobe²,

Fujimoto³

et al. 2015

AIAA Journal

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Aerodynamics of cambered airfoils are investigated numerically, using NACA four-digit series of 6% thickness at low Reynolds number Re = 10, 000, and moderate Mach number M = 0.2, by focusing on the relation of aeroacoustic effects and hydrodynamic flow unsteadiness. Two-dimensional numerical simulations show that the onset of an acoustic feedback loop (AFL) leads to an abrupt increase in lift force. Associated with the feedback process, the evolution of two-dimensional vortices in the suction-side boundary layer shifts a separation bubble toward the leading edge, which causes a relatively steep pressure recovery near the trailing edge. Through a parametric study on airfoil shape, the aerodynamically favorable feature of aft camber is further enhanced with the presence of an AFL. In addition, the aft camber airfoil successfully forms a laminar separation bubble in three-dimensional calculations at the present Reynolds number, developing transitional behavior on the suction side, supposedly prompted by the airfoil tones. Although the boundary layer shows three-dimensional complexity, still the formation of an AFL is strongly suggested, via the comparison of spanwise correlations.

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Multi‐size‐mesh multi‐time‐step algorithm for noise computation on curvilinear meshes

Garrec¹,

Gloerfelt

Corre

2013

Numerical Methods in Fluids

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Direct simulations of trailing-edge noise generation from two-dimensional airfoils at low Reynolds numbers

Cited by 41 publications

References 37 publications

Frequency Control of Unstable Disturbances in a Two-Dimensional Jet by Means of an Artificial Acoustic Loop

Frequency Control of Unstable Disturbances in a Two-Dimensional Jet by Means of an Artificial Acoustic Loop

Self-Noise Effects on Aerodynamics of Cambered Airfoils at Low Reynolds Number

Multi‐size‐mesh multi‐time‐step algorithm for noise computation on curvilinear meshes

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