On secondary tones arising in trailing-edge noise at moderate Reynolds numbers

Ricciardi, Túlio Rodarte; Arias-Ramírez, Walter; Wolf, William

doi:10.1016/j.euromechflu.2019.08.015

Cited by 26 publications

(42 citation statements)

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“…This frequency range corresponds to that where the most amplified modes from the linear The repeating patterns in the pressure signal show that the feedback mechanism has a period of t ≈ 2.0, related to the lower tone in the spectrum at St = 0.5. Destructive and constructive interference of vortical structures during the pairing process leads to an amplitude modulation of the signal (Desquesnes et al 2007;Pröbsting et al 2014;Ricciardi et al 2020). The modulation mechanism from the 2-D simulations performed in these references differs from the current 3-D case, where turbulent transition occurs.…”

Section: On Vortex Merging and Phase Interferencementioning

confidence: 83%

Transition, intermittency and phase interference effects in airfoil secondary tones and acoustic feedback loop

2022

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A large eddy simulation is performed to study secondary tones generated by a NACA0012 airfoil at angle of attack of $\alpha = 3^{\circ}$ with freestream Mach number of $M_{\infty} = 0.3$ and Reynolds number of $Re = 5 \times 10^4$ . Laminar separation bubbles are observed over the suction side and near the trailing edge, on the pressure side. Vortex shedding occurs aft of the suction side separation bubble, and vortex interaction results in merging or bursting such that coherent structures or turbulent packets are advected towards the trailing edge. This mechanism modulates the amplitude of the incident pressure signal, leading to different levels of noise emission. Despite the intermittent occurrence of laminar–turbulent transition, the noise spectrum depicts a main tone with multiple equidistant secondary tones. To understand the role of flow instabilities on the tones, the linearised Navier–Stokes equations are examined in their operator form through biglobal stability and resolvent analyses, and by time evolution of disturbances using a matrix-free method. These linear global analyses reveal amplification of disturbances over the suction side separation bubble. Spanwise-averaged pressure fluctuations elucidate aspects of the acoustic feedback loop mechanism in the nonlinear solutions. This feedback process is self-sustained by acoustic waves radiated from the trailing edge, which reach the most sensitive flow location near the leading edge, as identified by the resolvent analysis. Flow disturbances arising from secondary diffraction and phase interference among the most unstable frequencies computed in the eigenspectrum are shown to have an important role in the feedback loop.

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Section: On Vortex Merging and Phase Interferencementioning

confidence: 83%

Transition, intermittency and phase interference effects in airfoil secondary tones and acoustic feedback loop

2022

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“…Flow instabilities develop over the airfoil suction side at Re = 10 5 as discussed by Ricciardi et al [39]. These flow structures can be seen in Fig.…”

Section: B Reynolds Number 100000mentioning

confidence: 57%

“…In the former case, the noise spectrum is composed of a single tone at the vortex shedding frequency and its harmonics. For the latter case, a main tone is expected with additional secondary tones superposed on a broadband spectrum, as shown by [39].…”

Section: A Flow Simulationsmentioning

confidence: 93%

“…Different grid setups are used for the two Reynolds numbers analyzed as shown in Table 1 and they provide sufficient resolution for the present simulations according to [21,39]. This table also presents the non-dimensional time steps Δ𝑡 sim employed in each simulation, where the time scales are presented in nondimensional form with respect to 𝑈 ∞ and 𝐿.…”

Section: A Flow Simulationsmentioning

confidence: 99%

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Extremum Seeking Control Applied to Airfoil Trailing-Edge Noise Suppression

Déda

Wolf

2022

AIAA Journal

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Extremum seeking control (ESC) and its slope seeking generalization are applied in a highfidelity flow simulation framework for reduction of acoustic noise generated by a NACA0012 airfoil. Two Reynolds numbers are studied for which different noise generation mechanisms are excited. For a low Reynolds number flow, the scattering of vortex shedding at the airfoil trailing edge produces tonal noise while, for a moderate Reynolds number case, boundary layer instabilities scatter at the trailing edge leading to noise emission at multiple tones superimposed on a broadband hump. Different control setups are investigated and they are configured to either find an optimal steady actuator intensity or an optimal position for a blowing/suction device. Implementation details are discussed regarding the control modules and design of digital filters. Analyses of physical phenomena as well as of relevant behavior of the actuated * PhD candidate, Department of Energy.

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“…Other TE noise sources exist, such as the vortex shedding entailed by a blunted trailing edge (which also generates a strong tonal, dipolar acoustic emission), or the flow separation occurring in the early stage of stall (as opposed to the deep stall one, which rather results in noise radiating from the entire airfoil). Given its multiple components and complex physics, the airfoil trailing edge (TE) noise is still only partly understood [1][2][3], despite half a century of investigations using either experimental [1,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], theoretical [15][16][17][18][19], or computational [20][21][22][23][24][25] means.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of the Acoustic Installation Effects in Closed-Vein Wind Tunnels for the Experimental Characterization of Trailing Edge Noise

Redonnet

2021

Applied Sciences

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This study focuses on the acoustic installation effects that may occur during typical aeroacoustic experiments when the latter are conducted in a closed-vein wind tunnel. More precisely, in regard to the specific problem of airfoil trailing edge noise, an analytical model is derived, which allows predicting the wall-induced reverberation effects that such a noise shall be subjected to, when radiating within a closed-vein, hard-wall, wind tunnel. These effects are then assessed through a parametric investigation so as to characterize their impact on in situ acoustic measurements that would be performed using flush-mounted microphones located on the vein’s walls. From a phenomenological perspective, the study highlights how important the reverberation effects by the vein can be. In particular, results reveal how their impact on the noise measurements may greatly vary, depending on the trailing edge noise source location (i.e., the airfoil incidence) and, to a lesser extent, its frequency. The outcomes allow identifying these locations where the installation effects are least, i.e., where to better position a flush-mounted microphone, should in situ noise measurements be conducted. From a methodological viewpoint, the study showcases how the proposed formalism could constitute a simple albeit useful diagnosis tool for mitigating the experimental biases weighing on airfoil trailing edge noise tests to be conducted within closed-vein facilities, whether this would be done a priori by flush-mounting the microphone(s) where these biases are minimal or a posteriori by de-biasing the noise measurements accordingly.

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On secondary tones arising in trailing-edge noise at moderate Reynolds numbers

Cited by 26 publications

References 32 publications

Transition, intermittency and phase interference effects in airfoil secondary tones and acoustic feedback loop

Transition, intermittency and phase interference effects in airfoil secondary tones and acoustic feedback loop

Extremum Seeking Control Applied to Airfoil Trailing-Edge Noise Suppression

Theoretical Study of the Acoustic Installation Effects in Closed-Vein Wind Tunnels for the Experimental Characterization of Trailing Edge Noise

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