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The flow around an axisymmetric hull, with and without appendages, is investigated using large eddy simulation (LES), detached eddy simulation (DES), and Reynolds averaged Navier Stokes (RANS) models. The main objectives of the study is to investigate the effect of the different simulation methods and to demonstrate the feasibility of using DES and LES on relatively coarse grids for submarine flows, but also to discuss some generic features of submarine hydrodynamics. For this purpose the DARPA Suboff configurations AFF1 (bare hull) and AFF8 (fully appended model) are used. The AFF1 case is interesting because it is highly demanding, in particular for LES and DES, due to the long midship section on which the boundary layer is developed. The AFF8 case represents the complex flow around a fully appended submarine with sail and aft rudders. An actuator disc model is used to emulate some of the effects of the propulsor for one of the AFF8 cases studied. Results for the AFF8 model are thus presented for both "towed" and "self-propelled" conditions, where as for the bare hull, only a "towed" condition is considered. For the AFF1 and the "towed" AFF8 cases experimental data are available for comparison, and the results from both configurations show that all methods give good results for first-order statistical moments although LES gives a better representation of structures and second-order statistical moments in the complex flow in the AFF8 case.

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In this work, we use large eddy simulation (LES) to study the influence of grid and subgrid model on the lift and drag force predictions of a fixed cylinder undergoing streamwise sinusoidal oscillations in a steady flow, resulting in a varying Reynolds number, Re, within the range 405 ≤ Re ≤ 2482. This benchmark case is a first step toward studying engineering applications related to flow-induced vibrations. We examine the influence of both grid resolution and the subgrid model using implicit and explicit LES. The methodology used, LES based on a finite-volume method capable of handling moving meshes, are found to provide force predictions that agree well with experimentally measured data, with respect both to the overall flow development and force magnitude.

The Siemens gas turbine SGT-800 has an annular combustor and 30 dry low emission burners. In order to further reduce the emission levels and to obtain improved understanding of the flow and associated flame dynamics, single burner rig tests have been performed. The laboratory measurements are complemented by Large Eddy Simulation (LES) to analyze the effect on the flame dynamics due to the transient fuel distribution and mixing process in the burner. The study includes both atmospheric and high pressure conditions. The computational model was developed jointly by Siemens Industrial Turbomachinery AB (SIT) and FOI. It is based on a finite rate chemistry LES model using a Partially Stirred Reactor (PaSR) turbulence chemistry interaction model and a two-step CH4/air mechanism developed by FOI. The results are compared to measurements performed jointly by SIT and Lund Institute of Technology. The experimental data includes wall temperature, pressure fluctuations, light intensity variation and simultaneous Planar Laser Induced Fluorescence of OH and acetone. The study is further complemented by Reynolds Averaged Navier-Stokes (RANS) calculations of the fuel concentration field evaluated to laser measurements in a water rig using the same burner configuration. Different burner fuel distributions are examined and the corresponding influence on the downstream mixing, fuel distribution and flame dynamics are studied. The results indicate that the fuel distribution upstream the flame, the detailed modeling of the fuel supply manifold, including the specification of numerical boundary conditions, and the flow in the fuel and air supply pipes, have significant influence on the flame dynamics. This is proven by the successful combustion LES of an unstable flame that experiences high flame dynamics and that a modification of the boundary conditions alters the dynamics resulting in a more stable flame. This is well in accordance with the experimental data and previous experience at SIT. The modal structures caused by the interaction between the flow, acoustics and flame dynamics are analyzed using the Proper Orthogonal Decomposition (POD) technique. The dominating modes in general originate from the burner mixing tube air-fuel-mass flow-interaction and flame-combustion chamber interaction.