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

Abstract

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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Identifiers

ORCID for Markus Zauner: orcid.org/0000-0002-6644-2990

ORCID for Neil Sandham: orcid.org/0000-0002-5107-0944

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