Aerodynamic Control of Low-Reynolds-Number Airfoil with Leading-Edge Protuberances

Zhang, M. M.; Wang, G. F.; Xu, Jiakuan

doi:10.2514/1.j052319

Cited by 116 publications

(64 citation statements)

References 43 publications

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“…Additionally, Guerreiro & Sousa (2012) reported that the performance of an undulated wing increased with its aspect ratio. On the other hand, in the cases with an infinite span, the results show that WLEs tend to result in an earlier stall than conventional SLEs (straight leading edges) although the stall process is less abrupt and the post-stall performance (lift-to-drag ratio) may be higher (Johari et al 2007;Miklosovic et al 2007;Hansen et al 2011;Zhang et al 2013;Favier et al 2012;Rostamzadeh et al 2014;Skillen et al 2015).…”

Section: Introductionmentioning

confidence: 84%

A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge

Pérez-Torró

Kim

2017

J. Fluid Mech.

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A numerical investigation on the stalled flow characteristics of a NACA0021 aerofoil with a sinusoidal wavy leading edge (WLE) at Re ∞ = 1.2×105 and α = 20• is presented in this paper. It is observed that laminar separation bubbles (LSBs) form at the trough areas of the WLE in a collocated fashion rather than uniformly/periodically distributed over the span. It is found that the distribution of LSBs and its influence on the aerodynamic forces is strongly dependent on the spanwise domain size of the simulation, i.e. the wavenumber of the WLE used. The creation of a pair of counter-rotating streamwise vortices from the WLE and their evolution as an interface/buffer between the LSBs and the adjacent fully separated shear layers are discussed in detail. The current simulation results confirm that an increased lift and a decreased drag are achieved by using the WLEs compared to the straight leading edge (SLE) case, as observed in previous experiments. Additionally, the WLE cases exhibit a significantly reduced level of unsteady fluctuations in aerodynamic forces at the frequency of periodic vortex shedding. The beneficial aerodynamic characteristics of the WLE cases are attributed to the following three major events observed in the current simulations: (1) the appearance of a large low-pressure zone near the leading edge created by the LSBs; (2) the reattachment of flow behind the LSBs resulting in a decreased volume of the rear wake; and, (3) the deterioration of von-Kármán (periodic) vortex shedding due to the breakdown of spanwise coherent structures.

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Section: Introductionmentioning

confidence: 84%

A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge

Pérez-Torró

Kim

2017

J. Fluid Mech.

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“…Undulated LEs (with tubercles, protuberance or waviness) inspired by the flippers of humpback whales (Fish & Battle 1995;Miklosovic et al 2004) have been studied in recent years with regard to their benefits in terms of improved aerodynamic/hydrodynamic performance, particularly at high angles of attack close to the stall (Johari et al 2007;Yoon et al 2011;Hansen et al 2011;Guerreiro & Sousa 2012;Zhang et al 2013;Skillen et al 2014). Most of this work demonstrates that these LE modifications significantly improve the post-stall characteristics whereas they may adversely affect the pre-stall performance.…”

Section: Introductionmentioning

confidence: 99%

On the reduction of aerofoil–turbulence interaction noise associated with wavy leading edges

2016

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An aerofoil leading-edge profile based on wavy (sinusoidal) protuberances/tubercles is investigated to understand the mechanisms by which they are able to reduce the noise produced through the interaction with turbulent mean flow. Numerical simulations are performed for non-lifting flat-plate aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) subjected to impinging turbulence that is synthetically generated in the upstream zone (freestream Mach number of 0.24). Full threedimensional Euler (inviscid) solutions are computed for this study thereby eliminating self-noise components. A high-order accurate finite-difference method and artefact-free boundary conditions are used in the current simulations. Various statistical analysis methods, including frequency spectra, are implemented to aid the understanding of the noise-reduction mechanisms. It is found with WLEs, unlike the SLE, that the surface pressure fluctuations along the leading edge exhibit a significant source cut-off effect due to geometric obliqueness which leads to reduced levels of radiated sound pressure. It is also found that there exists a phase interference effect particularly prevalent between the peak and the hill centre of the WLE geometry, which contributes to the noise reduction in the mid-to high-frequency range.

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“…It has long been established that introducing LE serrations on aerofoils can improve their aerodynamic performance at post-stall conditions (Skillen et al 2014;Zhang et al 2013;Hansen et al 2011;Yoon et al 2011;Johari et al 2007). Collins (1981) has observed that the presence of leading edge serrations on wings can improve the low-speed lift and stall performance of aircraft during take-off and landing.…”

Section: Introductionmentioning

confidence: 99%

“…The significance of these vortices in affecting aerodynamic behaviour was also observed by Stanway (2008) in PIV measurements of the flow in the vicinity of a serrated leading edge. A number of researchers (Fish & Lauder 2006;Fish et al 2011;Zhang et al 2013;Van Nierop et al 2008) have investigated the mechanism by which stall can be delayed by the introduction of serrations at the aerofoil leading edge. They observed that the LE serrations generate streamwise vortices, which were attributed to greatly enhanced momentum transfer.…”

Section: Introductionmentioning

confidence: 99%

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

et al. 2017

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This paper presents the results of a detailed experimental investigation into the effectiveness of sinusoidal leading edge serrations on aerofoils for the reduction of the noise generated by the interaction with turbulent flow. A detailed parametric study is performed to investigate the sensitivity of the noise reductions to the serration amplitude and wavelength. The study is primarily performed on flat plates in an idealized turbulent flow, which we demonstrate captures the same behaviour as when identical serrations are introduced onto 3D aerofoils. The influence on the noise reduction of the turbulence integral length-scale is also studied. An optimum serration wavelength is identified whereby maximum noise reductions are obtained, corresponding to when the transverse integral length-scale is roughly one-forth the serration wavelength. This paper proves that, at the optimum serration wavelength, adjacent valley sources are excited incoherently. One of the most important findings of this paper is that, at the optimum serration wavelength, the sound power radiation from the serrated aerofoil varies inversely proportional to the Strouhal number St h = f h U , where f , h and U are frequency, serration amplitude and flow speed, respectively. A simple model is proposed to explain this behaviour. Noise reductions are observed to generally increase with increasing frequency until the frequency at which aerofoil self-noise dominates the interaction noise. Leading edge serrations are also shown to reduce trailing edge self-noise. The mechanism for this phenomenon is explored through PIV measurements. Finally, the lift and drag of the serrated aerofoil are obtained through direct measurement and compared against the straight edge baseline aerofoil. It is shown that aerodynamic performance is not substantially degraded by the introduction of the leading edge serrations on the aerofoil.

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Aerodynamic Control of Low-Reynolds-Number Airfoil with Leading-Edge Protuberances

Cited by 116 publications

References 43 publications

A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge

A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge

On the reduction of aerofoil–turbulence interaction noise associated with wavy leading edges

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

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