Scale-resolving simulations and data-driven modal analysis of turbulent transonic buffet cells on infinite swept wings
Pith reviewed 2026-05-16 13:50 UTC · model grok-4.3
The pith
Transonic buffet on swept wings arises from coexisting 2D shock oscillations and 3D separation instabilities.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Transonic buffet on infinite wings arises from the superposition of distinct but coexisting 2D shock motion and separation-driven 3D instabilities, with mean flow separation at the shock identified as a necessary condition for dominant 3D buffet dynamics to emerge. In the minimally separated case the shock motion remains spanwise uniform with only weak intermittent cells near the trailing edge. When mean separation increases, pronounced three-dimensional cells appear with a spanwise wavelength of one to 1.5 chord lengths; the quasi-stationary low-frequency separation mode identified on unswept wings becomes a traveling wave whose frequency shifts upward with sweep.
What carries the argument
Implicit large-eddy simulations combined with spectral proper orthogonal decomposition on span-periodic domains up to aspect ratio three.
If this is right
- The frequency and structure of the two-dimensional shock mode remain essentially unchanged when sweep is added.
- The three-dimensional separation mode increases in both frequency and energy content with sweep while its spanwise wavelength stays constant.
- Dominant three-dimensional buffet cells emerge only after the mean flow reaches significant separation at the shock foot.
- The low-frequency separation mode that is quasi-stationary on unswept wings becomes a spanwise-traveling wave once sweep is present.
Where Pith is reading between the lines
- Control strategies aimed at transonic buffet could target reduction of shock-foot separation rather than direct suppression of shock motion.
- The same modal picture applied to finite-span wings would show how the infinite-wing cells couple to tip vortices and root effects.
- Reduced-order models used for aircraft load prediction must retain both the two-dimensional and three-dimensional mechanisms rather than treating buffet as a purely two-dimensional phenomenon.
Load-bearing premise
Periodic simulations on domains of aspect ratio three or less are assumed to let three-dimensional buffet cells develop freely without artificial spanwise confinement.
What would settle it
If three-dimensional buffet cells of the reported wavelength and strength fail to appear in simulations with much larger aspect ratios or in experiments on swept wings with artificially suppressed mean separation at the shock, the necessity of that separation would be refuted.
Figures
read the original abstract
Transonic buffet is a class of shock-wave/boundary-layer interaction known to exhibit self-sustained two-dimensional (2D) chordwise shock wave oscillations (Strouhal number St=0.05-0.1), and three-dimensional (3D) spanwise-modulated flow separation/reattachment (St=0.2-0.4). Due to computational cost, scale-resolving simulations of span-periodic configurations to date have been limited to narrow airfoils, insufficient to accommodate the 3D buffet cell instability reported in low-fidelity simulations and experiments. In this work, implicit large-eddy simulations (ILES) and modal analysis are performed on infinite swept wings up to AR=3. The sensitivity of the 2D and 3D modes to crossflow is detailed. Two flow conditions are examined, corresponding to minimally and largely separated mean flow at the shock location. For the minimally separated case, the shock dynamics remain essentially spanwise-uniform (quasi-2D), with only weak and intermittent separation cells confined to the trailing-edge region and exhibiting negligible interaction with the shock. In contrast, increased mean separation leads to the emergence of pronounced 3D buffet cells with a characteristic spanwise wavelength: 1-1.5c. SPOD reveals that a quasi-stationary low-frequency 3D separation mode previously identified on unswept wings (St=0.02) becomes a spanwise travelling mode as sweep is imposed, shifting monotonically to intermediate frequencies (St=0.06-0.35). The 2D shock mode is largely insensitive to sweep, whereas the frequency and energy content of the 3D mode increase with sweep while its wavelength remains unchanged. The results demonstrate that transonic buffet on infinite wings arises from the superposition of distinct but coexisting 2D shock motion and separation-driven 3D instabilities, with mean flow separation at the shock identified as a necessary condition for dominant 3D buffet dynamics to emerge.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper performs implicit large-eddy simulations (ILES) and spectral proper orthogonal decomposition (SPOD) modal analysis on spanwise-periodic infinite swept wings up to aspect ratio AR=3 to study transonic buffet. It contrasts two regimes: minimally separated mean flow at the shock, where shock motion remains quasi-2D with only weak trailing-edge 3D cells, versus largely separated flow, where pronounced 3D buffet cells of spanwise wavelength 1-1.5c emerge. The analysis shows the 2D shock mode is largely insensitive to sweep while the 3D separation mode shifts from quasi-stationary to traveling with increasing frequency and energy content; the central claim is that buffet arises from superposition of distinct 2D shock and 3D separation instabilities, with mean separation at the shock a necessary condition for dominant 3D dynamics.
Significance. If the results hold, the work advances understanding of 3D transonic buffet mechanisms on swept wings by demonstrating the coexistence of 2D shock oscillation and separation-driven 3D instabilities via scale-resolving simulations on domains larger than prior narrow-airfoil studies, together with data-driven modal analysis that tracks sweep-induced changes in mode frequency and wavelength. The identification of mean-flow separation as a necessary condition for 3D cell dominance provides a concrete criterion that could inform reduced-order modeling and control strategies.
major comments (2)
- [Numerical setup] Numerical setup (domain and boundary conditions): The spanwise-periodic domains limited to AR=3 for reported 3D cell wavelengths of 1-1.5c admit at most two to three cells; periodicity then enforces discrete integer-mode selection that may artificially confine or stabilize wavelengths, directly undermining the claim that the observed modal superposition faithfully represents an unbounded infinite swept wing.
- [Results] Results section (quantitative support): No grid-convergence studies, experimental validation, or error bars are reported for the Strouhal numbers (St=0.05-0.1 for 2D shock, St=0.2-0.4 for 3D cells) or cell wavelengths that underpin the distinction between minimally and largely separated regimes and the necessity of mean separation; this weakens quantitative support for the central claim.
minor comments (2)
- [Abstract] Abstract: The two flow conditions are described only qualitatively as 'minimally' and 'largely' separated; explicit values of Mach number, Reynolds number, angle of attack, and sweep angles would improve reproducibility and context.
- [Throughout] Throughout: Notation for Strouhal number (St) and aspect ratio (AR) is used consistently but would benefit from a single definitions table or early section to aid readers unfamiliar with buffet literature.
Simulated Author's Rebuttal
We thank the referee for the positive assessment of our work and the constructive comments. We have carefully considered each point and provide our responses below, along with planned revisions to the manuscript.
read point-by-point responses
-
Referee: [Numerical setup] Numerical setup (domain and boundary conditions): The spanwise-periodic domains limited to AR=3 for reported 3D cell wavelengths of 1-1.5c admit at most two to three cells; periodicity then enforces discrete integer-mode selection that may artificially confine or stabilize wavelengths, directly undermining the claim that the observed modal superposition faithfully represents an unbounded infinite swept wing.
Authors: We acknowledge the referee's valid concern about the finite domain size potentially influencing the modal selection. However, the AR=3 domain was selected to allow for at least two full wavelengths of the observed 1-1.5c cells, which is consistent with the minimal domain sizes used in previous studies of 3D buffet cells on infinite wings. The fact that the 3D cells emerge only under largely separated conditions and their wavelengths remain consistent across sweep angles suggests that the dynamics are driven by the flow physics rather than domain constraints. The 2D shock mode being insensitive further supports the robustness. We disagree that this undermines the claim for the infinite wing, as the periodic boundary conditions are the standard approach to model infinite span. In the revised manuscript, we will add a discussion on the domain-size choice and its justification based on literature. revision: partial
-
Referee: [Results] Results section (quantitative support): No grid-convergence studies, experimental validation, or error bars are reported for the Strouhal numbers (St=0.05-0.1 for 2D shock, St=0.2-0.4 for 3D cells) or cell wavelengths that underpin the distinction between minimally and largely separated regimes and the necessity of mean separation; this weakens quantitative support for the central claim.
Authors: We agree that additional quantitative support would strengthen the manuscript. In the revised version, we will include a grid-convergence study comparing the key Strouhal numbers and wavelengths between the baseline grid and a refined grid (approximately 1.5 times more points in each direction), demonstrating that the reported values are converged within 5%. Error bars will be added to the reported St values based on variations over multiple shedding cycles. Regarding experimental validation, while we compare our 2D shock frequencies to established experimental data for unswept cases, direct validation for the 3D cell dynamics on swept wings at these conditions is not available in the open literature. We will expand the discussion to include more comparisons with existing low-fidelity and experimental results on 3D buffet cells. revision: yes
- Direct experimental validation for the specific 3D buffet cell dynamics on swept wings would require new experiments, which is beyond the scope of this numerical study.
Circularity Check
No circularity: results are direct outputs of ILES and SPOD on the simulated domains
full rationale
The paper contains no derivation chain. Its central claim—that transonic buffet on infinite wings arises from superposition of 2D shock motion and separation-driven 3D instabilities, with mean separation as a necessary condition—is presented as an empirical observation extracted from the ILES flow fields and SPOD modes at the two chosen conditions. No parameter is fitted to a subset of data and then relabeled as a prediction; no ansatz is smuggled via self-citation; no uniqueness theorem is invoked; and no quantity is defined in terms of itself. The domain-size concern (periodic AR=3) is an assumption about representativeness, not a circular reduction of the reported modal content to the input mesh or boundary conditions. The analysis is therefore self-contained against external benchmarks and receives the default non-circularity finding.
Axiom & Free-Parameter Ledger
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
implicit large-eddy simulations (ILES) and modal analysis... SPOD eigenvalue spectra... 2D shock-oscillation mode (St=0.08) and 3D buffet-cell mode
-
IndisputableMonolith/Foundation/AlexanderDuality.leanalexander_duality_circle_linking unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
spanwise wavelength λz≈1–1.5c... monotonic frequency increase with sweep
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
for the largest aspect ratio considered ofAR= 3. The 65% semi-span station of the NASA Common Research Model (CRM) wing is uniformly extruded in the periodic spanwise direction toL z = 3c(right plot in Fig.1). The sharp trailing edge configuration of this geometry was used. The numerical domain consists of one airfoil C-mesh connected to two wake blocks. ...
-
[2]
are compared. Vc is related to the Strouhal numberStas Vc =λ z ·f=λ z St·U ∞,2D c ,(9) based on the airfoil chord ofc= 1. The wavelength of the perturbation,λ z, is found to be independent of the sweep angle,λ, and is set by the aspect ratio (AR=L z/c= 3) of the spanwise-periodic airfoil asλ z =L z/2 = 1.5c at the present flow conditions and geometry. The...
-
[3]
B. H. K. Lee, Self-sustained shock oscillations on airfoils at transonic speeds, Progress in Aerospace Sciences37, 147 (2001)
work page 2001
-
[4]
N. F. Giannelis, G. A. Vio, and O. Levinski, A review of recent developments in the understanding of transonic shock buffet, Progress in Aerospace Sciences92, 39 (2017)
work page 2017
-
[5]
M. Iovnovich and D. E. Raveh, Numerical study of shock buffet on three-dimensional wings, AIAA Journal53(2), 449 (2015)
work page 2015
- [6]
-
[7]
Y. Ohmichi, T. Ishida, and A. Hashimoto, Modal decomposition analysis of three-dimensional transonic buffet phenomenon on a swept wing, AIAA Journal56, 3938 (2018)
work page 2018
-
[8]
E. Goncalves and R. Houdeville, Turbulence model and numerical scheme assessment for buffet computations, International Journal of Numerical Methods for Heat and Fluid Flow46, 1127 (2004)
work page 2004
-
[9]
M. Thiery and E. Coustols, Numerical prediction of shock induced oscillations over a 2D airfoil: Influence of turbulence modelling and test section walls, International Journal of Heat and Fluid Flow27, 661 (2006)
work page 2006
-
[10]
J. D. Crouch, A. Garbaruk, D. Magidov, and A. Travin, Origin of transonic buffet on aerofoils, Journal of Fluid Mechanics 628, 357 (2009)
work page 2009
-
[11]
M. Iovnovich and D. E. Raveh, Reynolds-Averaged Navier-Stokes study of the shock-buffet instability mechanism, AIAA Journal50, 880 (2012)
work page 2012
- [12]
-
[13]
J. D. Crouch, A. Garbaruk, and M. Strelets, Global instability in the onset of transonic-wing buffet, Journal of Fluid Mechanics881, 3 (2019)
work page 2019
-
[14]
F. Plante and E. Laurendeau, Simulation of transonic buffet using a time-spectral method, AIAA Journal57, 1275 (2019)
work page 2019
-
[15]
N. F. Giannelis, O. Levinski, and G. A. Vio, Influence of Mach number and angle of attack on the two-dimensional transonic buffet phenomenon, Aerospace Science and Technology78, 89 (2018)
work page 2018
-
[16]
E. Paladini, O. Marquet, D. Sipp, J.-C. Robinet, and J. Dandois, Various approaches to determine active regions in an unstable global mode: application to transonic buffet, Journal of Fluid Mechanics881, 617 (2019)
work page 2019
-
[17]
L. Poplinger, D. E. Raveh, and E. H. Dowell, Modal analysis of transonic shock buffet on 2d airfoil, AIAA Journal57 (2019)
work page 2019
-
[18]
A. Sansica, J.-C. Loiseau, A. Kanamori, M. Hashimoto, and J.-C. Robinet, System identification of two-dimensional transonic buffet, AIAA Journal60(2022)
work page 2022
-
[19]
Y. Iwatani, H. Asada, C.-A. Yeh, K. Taira, and S. Kawai, Identifying the self-sustaining mechanisms of transonic airfoil buffet with resolvent analysis, AIAA Journal61, 2400 (2023)
work page 2023
-
[20]
S. Deck, Numerical simulation of transonic buffet over a supercritical airfoil, AIAA Journal43(7), 1556 (2005)
work page 2005
- [21]
- [22]
-
[23]
E. Garnier and S. Deck,Large-Eddy Simulation of transonic buffet over a supercritical airfoil(Turbulence and Interactions (ed. M. Deville, T.-H. Le and P. Sagaut). Springer, Berlin, Heidelberg, 2013) pp. 135–141
work page 2013
-
[24]
Y. Fukushima and S. Kawai, Wall-modeled large-eddy simulation of transonic airfoil buffet at high reynolds number, AIAA Journal56(6), 1 (2018)
work page 2018
- [25]
- [26]
-
[27]
H. Song, M. L. Wong, A. S. Ghate, and S. K. Lele, Numerical study of transonic laminar shock buffet on the oalt25 airfoil, inAIAA SCITECH 2024 Forum(2024) Chap. AIAA 2024-2148
work page 2024
-
[28]
D. J. Lusher, A. Sansica, N. D. Sandham, J. Meng, B. Sikl´ osi, and A. Hashimoto, OpenSBLI v3.0: High-fidelity multi-block transonic aerofoil CFD simulations using domain specific languages on GPUs, Computer Physics Communications307, 109406 (2025)
work page 2025
-
[29]
D. J. Lusher, A. Sansica, and A. Hashimoto, Implicit large eddy simulations of three-dimensional turbulent transonic buffet on wide-span infinite wings, Journal of Fluid Mechanics1007, A26 (2025)
work page 2025
-
[30]
J. Dandois, I. Mary, and V. Brion, Large-eddy simulation of laminar transonic buffet, Journal of Fluid Mechanics850, 156–178 (2018)
work page 2018
- [31]
-
[32]
A. D’Aguanno, F. F. J. Schrijer, and B. W. van Oudheusden, Spanwise organization of upstream traveling waves in transonic buffet, Physics of Fluids33, 10.1063/5.0062729 (2021). 20
-
[33]
A. D’Aguanno, F. F. J. Schrijer, and B. W. van Oudheusden, Finite-wing and sweep effects on transonic buffet behavior, AIAA Journal60, 10.2514/1.J061974 (2022)
-
[34]
Y. Sugioka, T. Kouchi, and S. Koike, Experimental comparison of shock buffet on unswept and 10-deg swept wings, Experiments in Fluids63(2022)
work page 2022
-
[35]
A. Sansica, A. Hashimoto, S. Koike, and T. Kouchi, Side-wall effects on the global stability of swept and unswept super- critical wings at buffet conditions, inAIAA SCITECH 2022 Forum, AIAA Paper 2022-1972(2022)
work page 2022
-
[36]
J. Houtman, S. Timme, and A. Sharma, Resolvent analysis of a finite wing in transonic flow, Flow3, E14 (2023)
work page 2023
-
[37]
F. Sartor and S. Timme, Delayed detached–eddy simulation of shock buffet on half wing–body configuration, AIAA Journal 55, 1230 (2017)
work page 2017
-
[38]
A. Hashimoto, T. Ishida, T. Aoyama, Y. Ohmichi, T. Yamamoto, and K. Hayashi, Current progress in unsteady transonic buffet simulation with unstructured grid cfd code, in2018 AIAA Aerospace Sciences Meeting(2018) p. 0788
work page 2018
-
[39]
Y. Sugioka, S. Koike, K. Nakakita, D. Numata, T. Nonomura, and K. Asai, Experimental analysis of transonic buffet on a 3D swept wing using fast-response pressure-sensitive paint, Experiments in Fluids59(2018)
work page 2018
- [40]
-
[41]
Timme, Global instability of wing shock-buffet onset, Journal of Fluid Mechanics885(2020)
S. Timme, Global instability of wing shock-buffet onset, Journal of Fluid Mechanics885(2020)
work page 2020
-
[42]
Y. Sugioka, K. Nakakita, S. Koike, T. Nakajima, T. Nonomura, and K. Asai, Characteristic unsteady pressure field on a civil aircraft wing related to the onset of transonic buffet, Experiments in Fluids (2021)
work page 2021
-
[43]
A. Sansica and A. Hashimoto, Global stability analysis of full-aircraft transonic buffet at flight reynolds numbers, AIAA Journal61, 4437 (2023)
work page 2023
-
[44]
Y. Ohmichi, Variational mode decomposition–based nonstationary coherent structure analysis for spatiotemporal data, Aerospace Science and Technology149, 109162 (2024)
work page 2024
-
[45]
L. Jacquin, P. Molton, S. Deck, B. Maury, and D. Soulevant, Experimental study of shock oscillation over a transonic supercritical profile, AIAA J.47, 1985 (2009)
work page 1985
- [46]
-
[47]
D. J. Lusher, A. Sansica, and A. Hashimoto, Effect of Tripping and Domain Width on Transonic Buffet on Periodic NASA-CRM Airfoils, AIAA Journal , 1 (2024)
work page 2024
-
[48]
S. Deck and N. Renard, Towards an enhanced protection of attached boundary layers in hybrid rans/les methods, Journal of Computational Physics400, 10.1016/j.jcp.2019.108970 (2020)
-
[49]
E. Paladini, S. Beneddine, J. Dandois, D. Sipp, and J.-C. Robinet, Transonic buffet instability: From two-dimensional airfoils to three-dimensional swept wings, Phys. Rev. Fluids4, 103906 (2019)
work page 2019
-
[50]
F. Plante, J. Dandois, S. Beneddine, E. Laurendeau, and D. Sipp, Link between subsonic stall and transonic buffet on swept and unswept wings: from global stability analysis to nonlinear dynamics, Journal of Fluid Mechanics908, 10.1017/jfm.2020.848 (2021)
- [51]
-
[52]
F. F. Grinstein, L. G. Margolin, and W. J. Rider,Implicit large eddy simulation, Vol. 10 (Cambridge university press Cambridge, 2007)
work page 2007
-
[53]
P. R. Spalart, Strategies for turbulence modelling and simulations, International journal of heat and fluid flow21, 252 (2000)
work page 2000
- [54]
-
[55]
D. J. Lusher, S. P. Jammy, and N. D. Sandham, OpenSBLI: Automated code-generation for heterogeneous computing architectures applied to compressible fluid dynamics on structured grids, Computer Physics Communications267, 108063 (2021)
work page 2021
- [56]
- [57]
-
[58]
J.-B. Chapelier, D. J. Lusher, W. Van Noordt, C. Wenzel, T. Gibis, P. Mossier, A. Beck, G. Lodato, C. Brehm, M. Rug- geri, C. Scalo, and N. Sandham, Comparison of high-order numerical methodologies for the simulation of the supersonic Taylor–Green vortex flow, Physics of Fluids36, 055146 (2024)
work page 2024
-
[59]
D. J. Lusher, M. Zauner, A. Sansica, and A. Hashimoto, Automatic Code-Generation to Enable High-Fidelity Simulations of Multi-Block Airfoils on GPUs, inAIAA Scitech 2023 Forum, AIAA SciTech Forum(2023)
work page 2023
-
[60]
G. Mengaldo and R. Maulik, PySPOD: A Python package for Spectral Proper Orthogonal Decomposition (SPOD), Journal of Open Source Software6, 2862 (2021)
work page 2021
-
[61]
M. Rogowski, B. C. Yeung, O. T. Schmidt, R. Maulik, L. Dalcin, M. Parsani, and G. Mengaldo, Unlocking massively parallel spectral proper orthogonal decompositions in the PySPOD package, Computer Physics Communications , 109246 (2024)
work page 2024
-
[62]
A. Hamzehloo, D. J. Lusher, and N. D. Sandham, Direct numerical simulations and spectral proper orthogonal decompo- sition analysis of shocklet-containing turbulent channel counter-flows, International Journal of Heat and Fluid Flow104, 109229 (2023)
work page 2023
-
[63]
See Supplemental Material at [URL will be inserted by publisher] for animations of the SPOD modes
-
[64]
gov/crm-65-airfoil-sections (2012)
NASA-LaRC, Crm.65.airfoil sections., https://commonresearchmodel.larc.nasa. gov/crm-65-airfoil-sections (2012)
work page 2012
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.