LES and hybrid LES/RANS simulations for conjugate heat transfer over a matrix of cubes

Large Eddy Simulation (LES) and a novel k -l based hybrid LES/RANS approach have been applied to simulate a conjugate heat transfer problem involving flow over a matrix of surface mounted cubes. In order to assess the capability and reliability of the newly developed k -l based hybrid LES/RANS, numerical results are compared with new LES and existing RANS results. Comparisons include mean velocity profiles, Reynolds stresses and conjugate heat transfer. As well as for hybrid LES/RANS validation purposes, the LES results are used to gain insights into the complex flow physics and heat transfer mechanisms. Numerical simulations show that the hybrid LES/RANS approach is effective. Mean and instantaneous fluid temperatures adjacent to the cube surface are found to strongly correlate with flow structure. Although the LES captures more mean velocity field complexities, broadly time averaged wake temperature fields are found similar for the LES and hybrid LES/RANS. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Towards jet flow LES of conceptual nozzles for acoustic predictions

Progress in simulating chevron nozzle jet flows using ILES/RANS-ILES approaches and using the Ffowcs Williams and Hawkings (FW-H) surface integral method to predict the radiated far field sound is presented in this paper. With the focus on the realistic chevron geometries, SMC001 and SMC006, coarse and fine meshes are generated in the range of 3∼13 million mesh cells. Throughout this work, to minimize numerical dissipation introduced by mesh quality issues, the hexahedral cell type is used. Numerical simulations are then carried out with cell-vertex and cell-centered codes. Despite the modest grids, mean velocities and turbulent statistics are found to be in reasonable accord with measurements. Also, far field sound levels predicted by the FW-H post processor are encouraging. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc.

Hybrid LES - RANS of complex geometry jets

Large eddy simulation (LES) type studies are made of a realistic geometry coaxial nozzle with a pylon. For the LES, since the solver being used tends towards having dissipative qualities, the subgrid scale (SGS) model is omitted, giving Numerical LES (NLES). To overcome near wall streak resolution problems a near wall RANS (Reynolds averaged Navier Stokes) model is used giving a hybrid NLES-RANS approach.The pylon is shown to influence the flow development, having a significant impact on peak turbulence levels and spreading rates. The results show that real geometry effects are influential and should be taken into account when moving towards real engine simulations. If their effects are ignored then, based on the studies here, key turbulence parameters will have significant error.