The challenging case of the turbulent flow around a thin plate wind deflector, and its numerical prediction by LES and RANS models Luiz Eduardo B. Sampaio a , André Luiz T. Rezende b , Angela O. Nieckele c,n a Laboratory of Theoretical and Applied Mechanics – LMTA/PGMEC, Universidade Federal Fluminense – UFF, Rua Passo da Pátria 156 (bl E, s 216), Niterói, RJ 24210-240, Brazil b Department of Mechanical Engineering, Instituto Militar de Engenharia – IME, Praça General Tibúrcio 80, Urca, Rio de Janeiro, RJ 22290-270, Brazil c Department of Mechanical Engineering, Catholic University of Rio de Janeiro, PUC-Rio, Rua Marquês de São Vicente 225, Gávea, Rio de Janeiro, RJ 22451-900, Brazil article info Article history: Received 21 February 2014 Received in revised form 20 June 2014 Accepted 1 July 2014 Keywords: Flat plate Shallow incidence Anisotropic recirculation Reattachment LES RANS abstract The long recirculation bubble found in many industrial applications, mostly involving thin airfoils and thin plate wind deflectors, presents a challenging case for numerical models based on RANS methodology. A deeper understanding of this methodology and its limitations is gained through a series of numerical simulations of the incompressible flow around a thin flat plate of infinite wingspan at small incidences. In this numerically challenging flow, a thin recirculation zone with highly anisotropic turbulent structures is formed close to the leading edge after boundary layer separation. The importance of capturing anisotropy is thoroughly examined and quantitatively assessed in this paper, through a number of simulations employing both large eddy simulations (LES) and Reynolds average Navier– Stokes (RANS) approaches. The former is validated against previous wind tunnel experiment. Since the experimental data does not provide all tensor components to fully assess RANS quality, and LES results can be considered as a reliable source, they are employed in the full characterization of turbulence and in the assessment of the several RANS models predictions presented in this paper. Quantitative results are shown for the errors in capturing the anisotropy part of the Reynolds stress tensor for several RANS models, including Spalart–Almaras, κ ω SST and transition k ω SST. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Long and thin recirculation bubbles are found in many wind engineering and aerodynamic industrial application, such as in thin and membrane airfoils, wind deflectors, yacht sails, small wind turbine generators, orientation fins, microair vehicles, mis- sile and rocket fins, to cite a few (Cyr and Newman, 1996; Lian and Shyy, 2005; Lasher et al., 2005; Lasher and Sonnenmeier, 2008). However, its numerical prediction would still benefit from a more robust, efficient and precise methodology to cope with the physically complex flow, in which one can find features like highly anisotropic turbulent structures, shear layer development and transition to turbulence, separation, reattachment, relaminariza- tion in the backflow, secondary recirculation zones, post- reattachment boundary layer development, etc. All these features are also present in the flow around the geometrically simpler thin flat plate with a sharp leading edge at shallow incidence, as illustrated in Fig. 1. This simpler test case can thus serve as a benchmark for a critical evaluation of computa- tional turbulence models, ultimately leading to better methodol- ogies and helping the design of industrial devices in all of the afore-mentioned application fields. The thin airfoil bubble created on a plate with a sharp leading edge is characterized by a flow separation at the leading edge with a reattachment to the upper surface at a point which moves gradually downstream with increasing incidence. If the incidence angle is sufficiently small (usually smaller than 71), the flow reattaches. As shown in Fig. 1, there is a dividing streamline which separates the bubble from the outer flow and which rejoins the surface at the reattachment point. For greater angles, there is no reattachment point and the bubble enlarges downstream into the wake (Newman and Tse, 1992). Subsequent to separation, the shear layer distance to the wall increases rapidly, and the action of the viscous damping due to the high gradients in this region becomes weaker. Because of this deficit in the viscous damping, the shear layer is expected to suffer transition very close to the leading edge. The turbulent shear layer thickness increases quickly and has a high entrainment rate; it then reattaches further downstream and bifurcates. Some flow is Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jweia Journal of Wind Engineering and Industrial Aerodynamics http://dx.doi.org/10.1016/j.jweia.2014.07.007 0167-6105/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail addresses: luizebs@gmail.com (L.E.B. Sampaio), arezende@ime.eb.br (A. Luiz T. Rezende), nieckele@puc-rio.br (A. O. Nieckele). J. Wind Eng. Ind. Aerodyn. 133 (2014) 52–64