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The present work deals with a computational strategy coupling near-wall, eddyviscosity-based RANS models with LES within a zonal Hybrid LES/RANS (HLR) framework. Key questions concerning the coupling of both methods, the inherently steady RANS method and highly-unsteady LES method, are closely connected to the treatment at the interface separating both sub-regions. Large attention was paid to this problem and following three issues were highlighted: (1) the exchange of the variables across the LES/RANS interface was adjusted by implicit imposition of the condition of equality of the modelled turbulent viscosities (by assuming the continuity of their resolved contributions across the interface), enabling a smooth transition from the near-wall RANS layer to the off-wall LES sub-region; (2) utilisation of a dynamic, flow-dependent interface position in the course of the simulation. The control parameter k * representing the ratio of the modelled (SGS) to the total turbulent kinetic energy in the LES region, averaged over all grid cells at the interface on the LES side, is adopted; (3) the third issue, the present work is focussing on, addresses the usage of a special forcing technique, which compensates the loss of information due to strong damping caused by the presence of the RANS region (the typical outcome of such a circumstance is the so-called velocity mismatch in the region of interface) by creation of artificial and correlated fluctuations using a method originating from a digital-filterbased generation of inflow data for spatially developing DNS and LES due to Klein et al. (2003). Herewith, the recovery of the fluctuations on the LES side of the interface is accelerated and the afore-mentioned velocity bump is eliminated to a largest extent. The performances of the model are illustrated against the available DNS and fine-grid LES of periodic flows in a plane channel and over a 2-D smoothly contoured hill respectively.

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A method of coupling a low-Reynolds-number k–ε RANS (Reynolds-Averaged Navier-Stokes) model with Large-Eddy Simulation (LES) in a two-layer Hybrid LES/RANS (HLR) scheme is proposed in the present work. The RANS model covers the near-wall region and the LES model the remainder of the flow domain. Two different subgrid-scale (SGS) models in LES were considered, the Smagorinsky model and the one-equation model for the residual kinetic energy (Yoshizawa and Horiuti, 1985), combined with two versions of the RANS ε equation, one governing the “isotropic” (ε˜; Chien, 1982) and the other the “homogeneous” dissipation rate (εh; Jakirlic and Hanjalic, 2002). Both fixed and self-adjusting interface locations were considered. The exchange of the variables across the interface was adjusted by smoothing the turbulence viscosity either by adjusting the RANS model parameters, such as Cμ (Temmerman et al., 2005), or by applying an additional forcing at the interface using a method of digital-filter-based generation of inflow data for spatially developing DNS and LES due to Klein et al. (2003). The feasibility of the method was illustrated against the available DNS, fine- and coarse grid LES, DES (Detached Eddy Simulation) and experiments in turbulent flow over a backward-facing step at a low (Yoshioka et al., 2001) and a high Re number (Vogel and Eaton, 1985), periodic flow over a series of 2-D hills (Fro¨hlich et al., 2005) and in a high-Re flow over a 2-D, wall-mounted hump (Greenblat et al, 2004). Prior to these computations, the method was validated in a fully-developed channel flow at a moderate Reynolds number Rem ≈ 24000 (Abe et al., 2004).

For the prediction of hot gas side heat transfer in rocket thrust chambers, Astrium Space Transportation (ST) uses the second generation multiphase Navier Stokes solver Roc §am-II. To account for real-gas and condensation e¨ects, pressure-dependent and even multiphase §uid data are included in the chemistry tables used by the code. Thus, the changing §uid properties near the two-phase region as well as transformation from gaseous to liquid and even solid state are re §ected properly. Heat §ux measurements for a dedicated subscale test campaign with strongly cooled walls show a clearly increasing heat load as soon as the combustion gases condense at the wall, due to the released latent heat of condensation. Corresponding coupled Roc §am-II/CFX simulations show a good quantitative agreement in heat §ux for load cases with and without condensation, showing the ability of the code to correctly simulate §ows in the real-gas and even inside the two-phase region.

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A complementary experimental and computational study of the flow and mixing in a single annular gas turbine combustor has been carried out. The object of the investigation is a generic mixing chamber model, representing an unfolded segment of a simplified Rich-Quick-Lean (RQL) combustion chamber operating under isothermal, non-reacting conditions at ambient pressure. Two configurations without and with secondary air injection were considered. To provide an appropriate reference database several planar optical measurement techniques (time-resolved flow visualisation, PIV, QLS) were used. The PIV measurements have been performed providing profiles of all velocity and Reynolds-stress components at selected locations within the combustor. Application of a two-layer hybrid LES/RANS (HLR) method coupling a near-wall k − ε RANS model with conventional LES in the core flow was the focus of the computational work. In addition to the direct comparison with the experimental results, the HLR performance is comparatively assessed with the results obtained by using conventional LES using the same (coarser) grid as HLR and two eddy-viscosity-based RANS models. The HLR model reproduced all important flow features, in particular with regard to the penetrating behaviour of the secondary air jets, their interaction with the swirled main flow, swirl-induced free recirculation zone evolution and associated precessing-vortex core phenomenon in good agreement with experimental findings.