Tomographic-PIV investigation of the flow over serrated trailing-edges

Avallone, Francesco; León, Carlos Arce; Pröbsting, Stefan; Lynch, Kyle P.; Ragni, Daniele

doi:10.2514/6.2016-1012

Cited by 17 publications

(28 citation statements)

References 26 publications

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“…Figures 10 and 11 show the spatial distributions of Φ v v and Φ w w over four separate narrow frequency bands corresponding to Strouhal numbers St = f δ 95 /U ∞ equal to 0.5, 1, 2, and 3. Frequency spectra are left to the interested reader in Avallone et al 9 Over the span, the maximum intensity of both Φ v v ( Figure 10) and Φ w w (Figure 11) was measured in the wake in between the serration teeth. The intensity increases along the downstream direction.…”

Section: Spectral and Spatial Distribution Of Turbulent Fluctuationsmentioning

confidence: 99%

“…For the aforementioned applications, the most relevant mechanisms are related to the interaction of the turbulent boundary layer with the airfoil trailing edge, especially at low Mach numbers. 3 In the past, several passive noise-mitigation solutions have been proposed with the goal to alleviate this contribution, e.g., trailing-edge brushes, 4 sinusoidal and sawtooth serrations, [5][6][7][8][9][10][11][12] slits, 13,14 and randomly shaped trailing edges. 15 In the past decade, many analytical, [16][17][18][19] experimental, 5,9,11,20 and numerical studies 1,[21][22][23] have appointed sawtooth serrations as one of the most promising solutions.…”

Section: Introductionmentioning

confidence: 99%

“…The length of the serration was chosen to be approximately equal to two times the length of the boundary layer thickness based on 95% of the free-stream velocity (δ 95 , based on XFOIL 37 computations) for the tested Reynolds number. Avallone et al 9 reported noise measurements and demonstrated that the serrations under investigation reduce noise for chord-based Reynolds numbers Re c > 480 000.…”

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confidence: 99%

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Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

2016

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The three-dimensional flow field over the suction side of a NACA 0018 airfoil with trailing-edge serrations was studied by means of time-resolved tomographic particle image velocimetry. Mean flow results show that the boundary layer thickness decreases along the streamwise direction with a corresponding reduction of the size of the turbulent structures developing over the suction side of the serrations. At a positive angle of attack, streamwise-oriented and counter-rotating vortices aligned with the edge of the serrations are found to be the main features of the mean flow field. Their formation is attributed to the pressure imbalance between the two sides of the airfoil and the mixing layer at the edge. They locally modify the effective angle seen by the turbulent flow approaching the serrated edge. This effect may contribute to the serration underperformance in terms of noise reduction reported in literature. The spatial distribution of the spectra of the source term of the Poisson equation, which relates the velocity field to pressure fluctuations, suggests that the contribution of the serrations to far-field broadband noise is a function of the streamwise location. This observation is congruent with the spectra of the wall-normal and spanwise velocity fluctuations, which typically show low intensity close to the tips of the individual serrations. It follows that analytical models must take into account the local contribution to the far-field noise induced by the streamwise variation of the hydrodynamic pressure on the serration surface.

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Section: Spectral and Spatial Distribution Of Turbulent Fluctuationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

2016

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“…When compared to experimental results (e.g. [4,7,10,11]), the current triangular designs are not able to match the predicted noise reduction intensity. Recently, Lyu et al [14,17] developed a new semi-analytical model applying Amiet's trailing-edge noise theory [20] to sawtooth trailing edges.…”

Section: Introductionmentioning

confidence: 99%

“…Many passive mitigation strategies have been proposed to reduce this source of noise. Acoustic measurements, carried out both in wind tunnels and in-field, reported that sawtooth trailing-edge serrations offer the most effective noise reduction per simplicity of design [4][5][6][7][8][9][10][11]. Many analytical approaches have been proposed [13][14][15][16][17] to predict trailing-edge noise in presence of sawtooth trailing-edge serrations.…”

Section: Introductionmentioning

confidence: 99%

Concave serrations on broadband trailing edge noise reduction

Ragni

Avallone

Velden

2017

23rd AIAA/CEAS Aeroacoustics Conference

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The far-field noise and flow field of a novel curved trailing-edge serration (i.e. iron-shaped) are investigated. Spectra of the far-field broadband noise, directivity plots and the flow-field over the iron-shaped serration are obtained from numerical computations performed using a compressible Lattice-Boltzmann solver. The new design is compared to a conventional trailing-edge serration with a triangular geometry retrofitted to a NACA 0018 airfoil at zero degree angle of attack. The iron-shaped geometry is found to reduce far-field broadband noise of approximately 2 dB more than the conventional sawtooth serration for chord-based Strouhal numbers St c < 15. It is found that the larger noise reduction achieved by the iron-shaped trailing-edge serration is due to the mitigation of the scattered noise at the root, effect obtained by mitigating the interaction between the two sides of the serration, by delaying toward the tip both the outward and the downward flow motions present at the root.

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Trailing edge serrations effects on the aerodynamic performance of a NACA 64₃418

Llorente

Ragni

2018

Wind Energy

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A study of the aerodynamic performance of a NACA 643418 airfoil with trailing edge serrations is presented. For the prediction of the changes in lift due to the serration installation, an empirical law is derived that can be extended to typical cambered airfoils for wind turbine applications. The law is deduced from 2D and 3D Reynolds‐averaged Navier–Stokes simulations (RANS) of the flow over the airfoil. Lift and drag together with the changes in the wake flow due to the presence of the serrated edges are investigated. An additional study of the sensitivity of the results at Rec = 3·106 with respect to the turbulence modeling is carried out by using three different RANS models: Spalart–Allmaras, k‐omega SST, and Transition SST. Results show that the changes in lift due to trailing‐edge extensions are approximated by the effect of a split plate with reduced length.

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Tomographic-PIV investigation of the flow over serrated trailing-edges

Cited by 17 publications

References 26 publications

Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

Concave serrations on broadband trailing edge noise reduction

Trailing edge serrations effects on the aerodynamic performance of a NACA 64₃418

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Tomographic-PIV investigation of the flow over serrated trailing-edges

Cited by 17 publications

References 26 publications

Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

Concave serrations on broadband trailing edge noise reduction

Trailing edge serrations effects on the aerodynamic performance of a NACA 643418

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Product

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Trailing edge serrations effects on the aerodynamic performance of a NACA 64₃418