Applied large eddy simulation

Abstract

Large eddy simulation (LES) is now seen more and more as a viable alternative to current industrial practice, usually based on problem-specific Reynolds-averaged Navier-Stokes (RANS) methods. Access to detailed flow physics is attractive to industry, especially in an environment in which computer modelling is bound to play an ever increasing role. However, the improvement in accuracy and flow detail has substantial cost. This has so far prevented wider industrial use of LES. The purpose of the applied LES discussion meeting was to address questions regarding what is achievable and what is not, given the current technology and knowledge, for an industrial practitioner who is interested in using LES. The use of LES was explored in an application-centred context between diverse fields. The general flow-governing equation form was explored along with various LES models. The errors occurring in LES were analysed. Also, the hybridization of RANS and LES was considered. The importance of modelling relative to boundary conditions, problem definition and other more mundane aspects were examined. It was to an extent concluded that for LES to make most rapid industrial impact, pragmatic hybrid use of LES, implicit LES and RANS elements will probably be needed. Added to this further, highly industrial sector model parametrizations will be required with clear thought on the key target design parameter(s). The combination of good numerical modelling expertise, a sound understanding of turbulence, along with artistry, pragmatism and the use of recent developments in computer science should dramatically add impetus to the industrial uptake of LES. In the light of the numerous technical challenges that remain it appears that for some time to come LES will have echoes of the high levels of technical knowledge required for safe use of RANS but with much greater fidelity.

Computational Evaluation of Wind Loads on Low- and High- Rise Buildings

“…Because of these advancements, LES holds promise to become the future computational wind engineering (CWE) modeling for which turbulent flow is of pivotal importance Tucker and Lardeau, 2009;. In the present study, the Dynamic Smagornisky-Lilly subgrid-scale (SGS) model based on and Lily (1992) have been employed.…”

“…For pure LES simulation, the grid density increases with Re 1.8 in near-wall regions while in RANS grid clustering in the wallnormal direction is proportional to ln(Re) . Hence, for flows where the attached boundary layer plays a dominant role in the flows, coupling of the models (LES and RANS) is arguably a better strategy to drastically reduce the computational cost of a stand-alone LES (Leschiziner, 2009;Tucker and Lardeau, 2009;. Hybrid LES-RANS has been applied in various field of applications ranging from aeronautical (Forsythe et al, 2006), ground vehicles , scalar transport in urban environment (Lien et al, 2008) (Sreenivas et al, 2006) to buildings (Camarri et al, 2005;Wilson et al, 2006;Song and Park, 2009).…”

“…These basic strategies resolve most of the turbulent kinetic energy ( κ) of the flow and model the dissipation (ε) which are assumed to have a weak effect (see Fig. 2.2) (Walters and Bushan, 2005;Tucker and Lardeau, 2009;Frölich et al, 2008).…”

“…The ease of its implementation into an existing RANS solver makes PANS a more attractive proposition for CWE application (Frohlich and Terzi, 2008 numerical generation of transient inflow turbulence (Kraichan, 1970;Nozawa et al, , 2003; development of advanced sub-grid scale turbulence modeling techniques capable of solving unsteady three-dimensional boundary separated flows; and numerical discretization with conservation of physical quantities for modeling complicated geometry. Because of these LES holds promise to becoming the future CWE modeling option of where turbulent flow is of pivotal importance (Tucker and Lardeau, 2009;). …”

“…The use of LES as a wind load evaluation tool has been significantly improved in recent years through the following numerical techniques (a) numerical generation of transient inflow turbulence (Kraichan, 1970;Nozawa et al, , 2005, (b) development of efficient sub-grid scale turbulence modeling techniques suitable for unsteady three-dimensional boundary separated flows, and (c) numerical discretization with conservation of physical quantities for modeling complicated geometry . Because of these advancements, LES holds promise to become the future computational wind engineering (CWE) modeling for which turbulent flow is of pivotal importance Tucker and Lardeau, 2009;). In the present study, the Dynamic Smagornisky-Lilly subgrid-scale (SGS) model based on and Lily (1992) have been employed.…”