Detached-eddy simulation (DES) was first proposed in 1997 and first used in 1999, so its full history can be surveyed. A DES community has formed, with adepts and critics, as well as new branches. The initial motivation of high–Reynolds number, massively separated flows remains, for which DES is convincingly more capable presently than either unsteady Reynolds-averaged Navier-Stokes (RANS) or large-eddy simulation (LES). This review discusses compelling examples, noting the visual and quantitative success of DES. Its principal weakness is its response to ambiguous grids, in which the wall-parallel grid spacing is of the order of the boundary-layer thickness. In some situations, DES on a given grid is then less accurate than RANS on the same grid or DES on a coarser grid. Partial remedies have been found, yet dealing with thickening boundary layers and shallow separation bubbles is a central challenge. The nonmonotonic response of DES to grid refinement is disturbing to most observers, as is the absence of...

Detached-Eddy Simulation

https://www.colonius.caltech.edu/pdfs/ColoniusLele2004.pdf

Computational aeroacoustics: progress on nonlinear problems of sound generation

Usage of large-eddy simulation (LES) methods for calculation of turbulent flows has increased substantially in recent years. This paper attempts to 1) provide an assessment of the current capabilities of LES, 2) outline some recommended practices for using LES, and 3) identify future research needs. The assessment considers flow problems for which LES can be successfully applied today and flow problems for which LES still has limitations. The availability of LES and hybrid Reynolds-averaged Navier-Stokes (RANS)/LES in general-purpose codes is discussed. Several important issues for which the LES community has not yet reached a consensus are discussed. These include grid sensitivity studies, application of unstructured grid methods, upwind-biased solvers, and turbulence (subgrid) modeling including continuous hybrid RANS/LES approaches. A section on recommended practices and key considerations tries to provide guidance on some of the important items that need to be addressed in using LES. The paper concludes with a discussion of future research directions, with a focus on work needed to advance the capabilities and reliability of LES for analysis of turbulent flows.

/pdf/large-eddy-simulation-current-capabilities-recommended-4h3svw0l4f.pdf

Large-Eddy Simulation: Current Capabilities, Recommended Practices, and Future Research

I. Parallelism 1. Introduction 2. Parallel Computer Architectures 3. Parallel Programming Considerations II. Applications 4. General Application Issues 5. Parallel Computing in CFD 6. Parallel Computing in Environment and Energy 7. Parallel Computational Chemistry 8. Application Overviews III. Software technologies 9. Software Technologies 10. Message Passing and Threads 11. Parallel I/O 12. Languages and Compilers 13. Parallel Object-Oriented Libraries 14. Problem-Solving Environments 15. Tools for Performance Tuning and Debugging 16. The 2-D Poisson Problem IV. Enabling Technologies and Algorithms 17. Reusable Software and Algorithms 18. Graph Partitioning for Scientific Simulations 19. Mesh Generation 20. Templates and Numerical Linear Algebra 21. Software for the Scalable Solutions of PDEs 22. Parallel Continuous Optimization 23. Path Following in Scientific Computing 24. Automatic Differentiation V. Conclusion 25. Wrap-up and Features

Sourcebook of parallel computing

The emergence of biorobotic autonomous undersea vehicle (AUV) as a focus for discipline-integrated research in the context of underwater propulsion and maneuvering is considered within the confines of the Biorobotics Program in the Office of Naval Research. The significant advances in three disciplines, namely the biology-inspired high-lift unsteady hydrodynamics, artificial muscle technology and neuroscience-based control, are discussed in an effort to integrate them into viable products. The understanding of the mechanisms of delayed stall, molecular design of artificial muscles and the neural approaches to the actuation of control surfaces is reviewed in the context of devices based on the pectoral fins of fish, while remaining focused on their integrated implementation in biorobotic AUVs. A mechanistic understanding of the balance between cruising and maneuvering in swimming animals and undersea vehicles is given. All aquatic platforms, in both nature and engineering, except during short duration burst speeds that are observed in a few species, appear to lie within the condition where their natural period of oscillation equals the time taken by them to travel the distance of their own lengths. Progress in the development of small underwater experimental biorobotic vehicles is considered where the three aforementioned disciplines are integrated into one novel maneuvering device or propulsor. The potential in maneuvering and silencing is discussed.

Trends in biorobotic autonomous undersea vehicles

This paper presents a Spalart-Allmaras based Detached-Eddy Simulation (DES) of the Ahmed reference car model with 25° and 35° slant angles using unstructured grids and the solverCobalt. Comparisons are made to experimental laser doppler velocity measurements as well as total and surface pressure integrated drag. The Reynolds number based on body length was 2.78 ×106, making the boundary layers approaching the slant fully turbulent. The flow over the base slant in the experiments is attached at 25° and separated at 35°. This causes a large drop in the drag with the increased slant angle as the vortices on the side of the slant are weakened due to the separation. These cases stress turbulence models due to the need to accurately predict the boundary layer separation over the slant as well as predict the pressures in the massively separated base region accurately. The DES results are compared to the experiments as well as the Spalart-Allmaras RANS model. DES is seen to predict separation at 25◦ slant angle, in contrast to the experiments. Drag is relatively close to the experiments, but the distribution of drag is more on the rear than on the slant due to the separation. At the 35 ° slant angle, DES is in good agreement to the experimental drag, with the correct distribution, while RANS over-predicts the drag.

Detached-Eddy Simulation over a Reference Ahmed Car Model

Detached-eddy simulation of fighter aircraft at high alpha

Detached-eddy simulation (DES) is used to predict the massively separated flow around an F-15E at 65-deg angle of attack. The calculations are performed at flight conditions corresponding to a chord-based Reynolds number of 13.6 × 10 6 and Mach number of 0.3. Flowfield solutions are obtained using unstructured grids with the commercial solver Cobalt: the average mesh spacing from solid surfaces to the first cell center from the wall under one viscous unit. The influence of the mesh size is assessed using a series of three grids ranging from 2.85 × 10 6 cells to 10 × 10 6 cells. In addition, the influence of the time step is investigated using three simulations with varied time steps. DES predictions are assessed via comparison to Boeing's stability and control database as well as to solutions of the Reynolds-averaged Navies-Stokes (RANG) equations. These are steady, with the Spalart-Allmaras model. Both RANS and DES predictions of integrated forces exhibit a relatively weak dependence on the grid density for the range examined. In the DES the wake region is characterized by complex and chaotic three-dimensional structures with direct resolution of a reasonable range of length and timescales

Detached-Eddy Simulation of the F-15E at High Alpha

Progress on detached-eddy simulation of massively separated flows

The technical objective of the Second AIAA Computational Fluid Dynamics (CFD) Drag Prediction Workshop is to assess the state-of-the-art computational methods as practical aerodynamic tools for aircraft force-and-moment prediction of increasingly complex geometries. With more emphasis being placed on CFD methods to evaluate aircraft designs early in the design process, the ability to accurately predict the forces and moments, specifically drag, on an airliner configuration is important. Using the CFD code Cobalt, force-and-moment calculations are obtained on a civil transport geometry with and without engine nacelle and pylon

Kenneth E. Wurtzler

Papers

Detached-Eddy Simulation over a Reference Ahmed Car Model

Detached-eddy simulation of fighter aircraft at high alpha

Detached-Eddy Simulation of the F-15E at High Alpha

Progress on detached-eddy simulation of massively separated flows

Accurate drag prediction using Cobalt