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.

Large-eddy simulations and modal reconstruction of laminar transonic buffet

“…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.…”

“…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.…”

“…2020; Plante et al. 2020; Zauner & Sandham 2020 b ). In an experimental study of the laminar supercritical OALT25 profile, Brion et al.…”

“…For example, the presence of propagating pressure waves in the flow field is well-documented (Jacquin et al. 2009; Hartmann, Feldhusen & Schroder 2013; Zauner & Sandham 2020 b ). The predicted frequency has been shown to match with observed buffet frequency in some studies (Deck 2005; Xiao et al.…”

“…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.…”