Flow topology and acoustic emissions of trailing edge serrations at incidence

León, Carlos Arce; Ragni, Daniele; Pröbsting, Stefan; Scarano, Fulvio; Madsen, Jesper

doi:10.1007/s00348-016-2181-1

Cited by 71 publications

(75 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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%

“…Simultaneously, they decrease the spanwise correlation of the flow structures near the tip in the upper part of the boundary layer. A first attempt to relate the mean flow features near the serration surface to the acoustic underperformance of the serration was presented by Arce León et al 11 They observed an inward deflection of the streamlines toward the tip of the serration and concluded that this distortion of the near-wall streamlines cannot be the only reason for the discrepancy between the predicted and measured noise reduction.…”

mentioning

confidence: 99%

See 1 more Smart Citation

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

2016

View full text Add to dashboard Cite

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.

show abstract

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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

2016

View full text Add to dashboard Cite

show abstract

“…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: 80%

“…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%

“…[7,10,21,22]) have shown that the flow past serrated airfoils is strongly three dimensional, with vortical structures developing along the edges of the serrations. Flow measurements [7,10,24] and computations [22,25] showed that, even at small angles of attack, the turbulent flow tends to seep into the empty space in between serrations. This flow distortion is found to reduce the effective angle seen by the turbulent flow convecting over the edge of the serrations thus reducing the effectiveness of the serrations in mitigating far-field noise [21].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Concave serrations on broadband trailing edge noise reduction

Ragni

Avallone

Velden

2017

23rd AIAA/CEAS Aeroacoustics Conference

Self Cite

View full text Add to dashboard Cite

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.

show abstract

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

Llorente

Ragni

2018

Wind Energy

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Flow topology and acoustic emissions of trailing edge serrations at incidence

Cited by 71 publications

References 25 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

Contact Info

Product

Resources

About

Flow topology and acoustic emissions of trailing edge serrations at incidence

Cited by 71 publications

References 25 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

Contact Info

Product

Resources

About

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