Assessment of Reynolds stresses tensor reconstruction methods for synthetic turbulent inflow conditions. Application to hybrid RANS/LES methods Romain Laraufie, Sébastien Deck ⇑ Department of Applied Aerodynamics, ONERA – The French Aerospace Lab, F-92190 Meudon, France article info Article history: Received 14 May 2012 Received in revised form 16 April 2013 Accepted 22 April 2013 Available online 18 May 2013 Keywords: Turbulent inflow Reynolds stresses tensor Hybrid RANS/LES SEM ZDES Transition abstract Hybrid or zonal RANS/LES approaches are recognized as the most promising way to accurately simulate complex unsteady flows under current computational limitations. One still open issue concerns the tran- sition from a RANS to a LES or WMLES resolution in the stream-wise direction, when near wall turbulence is involved. Turbulence content has then to be prescribed at the transition to prevent from turbulence decay leading to possible flow relaminarization. The present paper aims to propose an efficient way to generate this switch, within the flow, based on a synthetic turbulence inflow condition, named Synthetic Eddy Method (SEM). As the knowledge of the whole Reynolds stresses is often missing, the scope of this paper is focused on generating the quantities required at the SEM inlet from a RANS calculation, namely the first and second order statistics of the aerodynamic field. Three different methods based on two dif- ferent approaches are presented and their capability to accurately generate the needed aerodynamic val- ues is investigated. Then, the ability of the combination SEM + Reconstruction method to manufacture well-behaved turbulence is demonstrated through spatially developing flat plate turbulent boundary lay- ers. In the mean time, important intrinsic features of the Synthetic Eddy method are pointed out. The necessity of introducing, within the SEM, accurate data, with regards to the outer part of the boundary layer, is illustrated. Finally, user’s guidelines are given depending on the Reynolds number based on the momentum thickness, since one method is suitable for low Reynolds number while the second is ded- icated to high ones with a transition located around Re h = 3000. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction The increasing interest brought to hybrid RANS-LES methods makes this approach more and more inevitable in the field of CFD. The main fact responsible for such a fad relies on its ability to treat industrial configurations, where the unsteady character of the flow field is of primary importance, under current computa- tional resources limitations (see the review by Sagaut and Deck (2009)). Nevertheless, further developments of these methods are still required, especially when the overall flow physics is driven by the near wall turbulence. For example, the inflow condition arises among the classical encountered problems. This issue is inherent to methods that intend to resolve the turbulent part of the flow. One should not be surprised to realize that inflow condi- tion methods are the same as those used for DNS or LES in the case of Wall Modelled Large Eddy Simulation (WMLES). Nevertheless, additional treatment can be needed (see Laraufie et al. (2011) for example). Reviews and hierarchical organizations of the various inflow generation methods were drawn by Sagaut et al. (2006) or more recently by Tabor and Baba-Ahmadi (2010). Three main fam- ilies seem to stand out according to Sagaut et al. (2006): databases generated by precursor simulations, recycling methods and syn- thetic turbulence. The main differences between all of them lie in the quality of the turbulence they generate, the computational dis- tance required to obtain a well-behaved turbulence, also called ‘‘adaptation distance’’, and last but not least, the extra cost they generate. Precursor calculations are well acknowledged to be an accurate way to initialize a simulation. However, this technique implies a heavy extra computational load and is restricted to simple cases. Recycling methods consist in extracting a plane several bound- ary layer thickness (d) downstream of the inlet and reintroducing it as inflow condition. This approach has long been favoured due to its simplicity and its short adaption distance. However, two main drawbacks have to be considered. A precursor calculation is still required to initialize the process. What is more, this method was designed for flat plate turbulent boundary layers and its extension to more complex geometries may face considerable problems. On 0142-727X/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ijheatfluidflow.2013.04.007 ⇑ Corresponding author. Tel.: +33 1 46 73 43 47; fax: +33 1 46 73 41 46. E-mail addresses: romain.laraufie@onera.fr (R. Laraufie), sebastien.deck@onera.fr (S. Deck). International Journal of Heat and Fluid Flow 42 (2013) 68–78 Contents lists available at SciVerse ScienceDirect International Journal of Heat and Fluid Flow journal homepage: www.elsevier.com/locate/ijhff