Detached-eddy simulation (DES) is well understood in thin boundary layers, with the turbulence model in its Reynolds-averaged Navier–Stokes (RANS) mode and flattened grid cells, and in regions of massive separation, with the turbulence model in its large-eddy simulation (LES) mode and grid cells close to isotropic. However its initial formulation, denoted DES97 from here on, can exhibit an incorrect behavior in thick boundary layers and shallow separation regions. This behavior begins when the grid spacing parallel to the wall Δ∥ becomes less than the boundary-layer thickness δ, either through grid refinement or boundary-layer thickening. The grid spacing is then fine enough for the DES length scale to follow the LES branch (and therefore lower the eddy viscosity below the RANS level), but resolved Reynolds stresses deriving from velocity fluctuations (“LES content”) have not replaced the modeled Reynolds stresses. LES content may be lacking because the resolution is not fine enough to fully support it, and/or because of delays in its generation by instabilities. The depleted stresses reduce the skin friction, which can lead to premature separation.

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A new version of detached-eddy simulation, resistant to ambiguous grid densities

A hybrid RANS-LES approach with delayed-DES and wall-modelled LES capabilities

Computational Fluid Dynamics: Principles and Applications, Third Edition presents students, engineers, and scientists with all they need to gain a solid understanding of the numerical methods and principles underlying modern computation techniques in fluid dynamics By providing complete coverage of the essential knowledge required in order to write codes or understand commercial codes, the book gives the reader an overview of fundamentals and solution strategies in the early chapters before moving on to cover the details of different solution techniques

	This updated edition includes new worked programming examples, expanded coverage and recent literature regarding incompressible flows, the Discontinuous Galerkin Method, the Lattice Boltzmann Method, higher-order spatial schemes, implicit Runge-Kutta methods and parallelization

	An accompanying companion website contains the sources of 1-D and 2-D Euler and Navier-Stokes flow solvers (structured and unstructured) and grid generators, along with tools for Von Neumann stability analysis of 1-D model equations and examples of various parallelization techniques



	
		Will provide you with the knowledge required to develop and understand modern flow simulation codes
	
		Features new worked programming examples and expanded coverage of incompressible flows, implicit Runge-Kutta methods and code parallelization, among other topics
	
		Includes accompanying companion website that contains the sources of 1-D and 2-D flow solvers as well as grid generators and examples of parallelization techniques

Computational Fluid Dynamics: Principles and Applications Ed. 3

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

The numerical simulation of high Reynolds number flows is hampered by model accuracy if the Reynolds-averaged Navier–Stokes (RANS) equations are used, and by computational cost if direct or large-eddy simulations (LES) that resolve the near-wall layer are employed. The cost of a calculation scales like the Reynolds number to the power 3 for direct numerical simulations, or 2.4 for LES, making the resolution of the wall layer at high Reynolds number infeasible even with the most advanced computers. In LES, an attractive alternative to compute high-Re flows is the use of wall-layer models, in which only the outer layer is resolved, while the near-wall region is modeled. Three broad classes of approaches are presently used: bypassing this region altogether using wall functions, solving a separate set of equations in the near-wall region, weakly coupled to the outer flow, or simulating the near-wall region in a global, Reynolds-averaged, sense. These approaches are discussed and their ranges of applicability are highlighted. Various unresolved issues in wall-layer modeling are presented.

Wall-layer models for large-eddy simulations

Direct- and Large Eddy Simulations of Turbulent Flow in CS0 Diffuser on Resolved and Under-resolved Meshes

This paper studies the level of confidence and applicability of CFD simulations using steady-state Reynolds-Averaged Navier-Stokes (RANS) in predicting aerodynamic performance losses on swept-wings due to contamination with ice accreted in-flight. The wing geometry selected for the study is the 65%-scale Common Research Model (CRM65) main wing, for which NASA Glenn Research Center’s Icing Research Tunnel has generated experimental ice shapes for the inboard, mid-span, and outboard sections. The reproductions at various levels of fidelity from detailed 3D scans of these ice shapes have been used in recent aerodynamic testing at the Office National d’Etudes et Recherches Aérospatiales (ONERA) and Wichita State University (WSU) wind tunnels. The ONERA tests were at higher Reynolds number range in the order of 10 million, while the WSU tests were in the order of 1 million. RANS CFD results for the lower-Reynolds 8.9% WSU model up to α = 10° were previously generated by University of Virginia and NASA Glenn Research Center using Ansys Fluent and k-ω SST on the clean and low-fidelity (smooth) iced wings. The current CFD study focuses on the high-fidelity ice shape, presenting RANS results for both low and high Reynolds numbers, for the full α sweep up to α = 25° for which there is experimental data on the iced wings. A straight-forward automatable CAD-to-solution workflow is established using surface curvature and proximity-based mesh sizing functions for grid generation. The simulations results include CL, CM, CD curves for both clean and iced wings, their comparison to the experimentally obtained counterparts, iced surface Cp distributions, and a detailed breakdown of the computational cost and user effort in generating these solutions.

Numerical Study of Iced Swept-Wing Performance Degradation using RANS

Publisher Summary
This chapter discusses the increasing computer performance and improved numerical methods that not only allow the numerical computation of more complex flow fields, but also enable the use of higher order turbulence models in Reynolds averaged Navier–Stokes computations. It presents the implementation of a Rejmolds-stress model (RSM) in a Navier–Stokes code. The RSM used in this study is the multiscale (MS) model. In this model, the Reynolds-stresses are partitioned into two sets of scales. The main part of this model, the pressure-strainterm, is identical to the Launder–Reece and Rodi model. The implementation of a RSM's into a Navier–Stoke code is not a trivial matter and can lead to severe stability problems. The discretization and the linearization of the equations are of crucial importance to the success of the computations. The chapter reviews the results for four increasingly complex flow fields.

Florian R. Menter

Papers

Direct- and Large Eddy Simulations of Turbulent Flow in CS0 Diffuser on Resolved and Under-resolved Meshes

Numerical Study of Iced Swept-Wing Performance Degradation using RANS

Higher Order Turbulence Model Predictions for Complex 2D and 3D Flowfields

Laminar-Turbulent Transition Prediction on Industrial CFD Applications