Modal Analysis of a Laminar-Flow Airfoil under Buffet Conditions at Re = 500,000

Zauner, Markus; Sandham, Neil D.

doi:10.1007/s10494-019-00087-z

Cited by 26 publications

(30 citation statements)

References 52 publications

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“…Here, we continue our studies on laminar buffet (Zauner et al. 2019; Zauner & Sandham 2020 a , b ) focusing on Dassault aviation's supercritical laminar V2C profile which complements those on the OALT25 profile carried out by others (Dandois et al. 2018; Brion et al.…”

Section: Introductionsupporting

confidence: 59%

“…2009), which is a scalable compressible flow solver with multi-block and shock-capturing capabilities and has been used previously to study buffet (Zauner et al. 2019; Zauner & Sandham 2020 a , b ). SBLI solves for the compressible Navier–Stokes equations which govern the flow evolution in a dimensionless form (see Zauner & Sandham 2020 b , pp.…”

Section: Methodsmentioning

confidence: 99%

“…Laminar buffet at a lower Reynolds number () was examined for the V2C profile in our previous studies (Zauner et al. 2019; Zauner & Sandham 2020 a , b ). Unlike Dandois et al.…”

Section: Introductionmentioning

confidence: 99%

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Large-eddy simulations and modal reconstruction of laminar transonic buffet

2022

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Transonic buffet refers to the self-sustained periodic motion of shock waves observed in transonic flows over wings and can limit the flight envelope of aircraft. Based on the boundary layer characteristics at the shock foot, buffet has been classified as laminar or turbulent and the mechanisms underlying the two have been proposed to be different (Dandois et al., J. Fluid Mech., vol. 18, 2018, pp. 156–178). The effect of various flow parameters (freestream Mach and Reynolds numbers and sweep and incidence angles) on laminar transonic buffet on an infinite wing (Dassault Aviation's supercritical V2C aerofoil) is reported here by performing large-eddy simulations (LES) for a wide range of parameters. A spectral proper orthogonal decomposition identified the presence of a low-frequency mode associated with buffet and high-frequency wake modes related to vortex shedding. A flow reconstruction based only on the former shows periodic boundary-layer separation and reattachment accompanying shock wave motion. A modal reconstruction based only on the wake mode suggests that the separation bubble breathing phenomenon reported by Dandois et al. is due to this mode. Together, these results indicate that the physical mechanisms governing laminar and turbulent buffet are the same. Buffet was also simulated at zero incidence. Shock waves appear on both aerofoil surfaces and oscillate out of phase with each other indicating the occurrence of a Type I buffet (Giannelis et al., Aerosp. Sci. Technol., vol. 18, 2018, pp. 89–101) on a supercritical aerofoil. These results suggest that the mechanisms underlying different buffet types are the same.

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Section: Introductionsupporting

confidence: 59%

Section: Methodsmentioning

confidence: 99%

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Large-eddy simulations and modal reconstruction of laminar transonic buffet

2022

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“…Those transonic-flow stability results on a NACA0012 aerofoil demonstrated good agreement with earlier experimental data (McDevitt & Okuno 1985). More recently, the ideas were successfully applied in the analysis of other aerofoils (Sartor et al 2015;Zauner & Sandham 2020) and three-dimensional infinite (Crouch et al 2019;Paladini 2019;Paladini et al 2019;Plante et al 2021) and finite (Timme & Thormann 2016;Timme 2020) wings. In those infinite-wing shock-buffet studies, the authors predicted both the quasi-two-dimensional aerofoil mode and presented spatial spanwise-periodic modes in the framework of biglobal stability analysis.…”

Section: Introductionmentioning

confidence: 99%

Triglobal infinite-wing shock-buffet study

Timme

2021

J. Fluid Mech.

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This article uses triglobal stability analysis to address the question of shock-buffet unsteadiness, and associated modal dominance, on infinite wings at high Reynolds number, expanding upon recent biglobal work, aspiring to elucidate the flow phenomenon's origin and characteristics. Infinite wings are modelled by extruding an aerofoil to finite aspect ratios and imposing a periodic boundary condition without assumptions on spanwise homogeneity. Two distinct steady base flows, spanwise uniform and non-uniform, are analysed herein on straight and swept wings. Stability analysis of straight-wing uniform flow identifies both the oscillatory aerofoil mode, linked to the chordwise shock motion synchronised with a pulsation of its downstream shear layer, and several monotone (non-oscillatory), spatially periodic shock-distortion modes. Those monotone modes become outboard travelling on the swept wing with their respective frequencies and phase speeds correlated with the sweep angle. In the limiting case of very small wavenumbers approaching zero, the effect of sweep creates branches of outboard and inboard travelling modes. Overall, triglobal results for such quasi-three-dimensional base flows agree with previous biglobal studies. On the contrary, cellular patterns form in proper three-dimensional base flow on straight wings, and we present the first triglobal study of such an equilibrium solution to the governing equations. Spanwise-irregular modes are found to be sensitive to the chosen aspect ratio. Nonlinear time-marching simulations reveal the flow evolution and distinct events to confirm the insights gained through dominant modes from routine triglobal stability analysis.

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“…This airfoil geometry was the subject of experimental [31,32] as well as numerical studies [33][34][35][36] and is also considered for our investigations. It is likely that, over some parameter ranges and airfoil geometries, different types of buffet exist (or can even coexist) ( [16,30,37]) and it is still unclear how they relate to each other and to turbulent cases [38].…”

Section: Introductionmentioning

confidence: 99%

Wide domain simulations of flow over an unswept laminar wing section undergoing transonic buffet

Zauner

Sandham

2020

Phys. Rev. Fluids

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Transonic buffet is an unsteady flow phenomenon that limits the safe flight envelope of modern aircraft. Scale-resolving simulations with span-periodic boundary conditions can provide detailed insight into the flow physics associated with buffet and can help to calibrate simplified models that are needed, for example, to develop more efficient wings based on laminar-flow supercritical sections. However, such simulations are often feasible only for severely restricted spanwise domains. In the current contribution, we analyse an unswept laminar-flow wing section (of Dassault Aviation's V2C profile) at a moderate Reynolds number of Re = 500,000 and a Mach number of M = 0.7 with spanwise domains equal to 5% and 100% of the airfoil chord. An implicit large-eddy simulation methodology, using a spectral error estimator to control the action of a high-order filter, is first validated against direct numerical simulations and then used for the domain width study. Quantitative differences, due to domain size, include an increase in amplitude and regularity of the buffet oscillations in the wider domain. Nevertheless, space-time analysis shows that key physical phenomena such as upstream-propagating shock waves are properly represented in the narrow domain and there is limited sensitivity to domain size of the aerodynamic coefficients. Even in the very wide domain, which is an order of magnitude wider than the largest turbulent structures measured at the trailing edge, certain features remain two-dimensional, including the shock and expansion waves that interact with the boundary layer upstream of transition. The transition mechanism is found to have subtle variations during a typical buffet cycle, with Kelvin-Helmholtz structures prominent during low-lift phases and oblique modes developing behind shock/boundarylayer interactions during high-lift phases. The availability of the wide-domain data is used for further study of the buffet mechanism, considering phase-averaged data and instantaneous flow fields to show the global structure of the buffet oscillation.

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Modal Analysis of a Laminar-Flow Airfoil under Buffet Conditions at Re = 500,000

Cited by 26 publications

References 52 publications

Large-eddy simulations and modal reconstruction of laminar transonic buffet

Large-eddy simulations and modal reconstruction of laminar transonic buffet

Triglobal infinite-wing shock-buffet study

Wide domain simulations of flow over an unswept laminar wing section undergoing transonic buffet

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