Will RANS Survive LES? A View of Perspectives

2004 ◽  
Author(s):  
K. Hanjalic´
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Hybrid Approaches ◽  
Large Eddy ◽  
The Future ◽  
Eddy Structures ◽  
Rans Models ◽  
High Reynolds

The paper provides a view of some developments and a perspective on the future role of the Reynolds-averaged Navier-Stokes (RANS) approach in the computation of turbulent flows and heat transfer in competition with Large-eddy simulations (LES). It is argued that RANS will further play an important role, especially in industrial and environmental computations, and that the future increase in the computing power will be used more to utilize advanced RANS models to shorten the design and marketing cycle rather than to yield the way to LES. We also discuss some current and future developments in RANS aimed at improving their performance and range of applicability, as well as their potential in hybrid approaches in combination with the LES strategy. Limitations in LES at high Reynolds (Re) and Rayleigh (Ra) number flows and heat transfer are revisited and some hybrid RANS/LES routes are discussed. The potential of very large eddy simulations (VLES) of flows dominated by (pseudo)-deterministic eddy structures, based on transient RANS (T-RANS) and similar approaches is discussed and illustrated in an example of “ultra-hard” (very high Ra) thermal convection.

Will RANS Survive LES? A View of Perspectives

2005 ◽  
Vol 127 (5) ◽  
pp. 831-839 ◽  
Author(s):  
K. Hanjalic
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Hybrid Approaches ◽  
Large Eddy ◽  
Eddy Structures ◽  
Rans Models ◽  
High Reynolds

The paper provides a view of some developments and a perspective on the future role of the Reynolds-averaged Navier-Stokes (RANS) approach in the computation of turbulent flows and heat transfer in competition with large-eddy simulations (LES). It is argued that RANS will further play an important role, especially in industrial and environmental computations, and that the further increase in the computing power will be used more to utilize advanced RANS models to shorten the design and marketing cycle rather than to yield the way to LES. We also discuss some current and future developments in RANS aimed at improving their performance and range of applicability, as well as their potential in hybrid approaches in combination with the LES strategy. Limitations in LES at high Reynolds (Re) and Rayleigh (Ra) number flows and heat transfer are revisited and some hybrid RANS/LES routes are discussed. The potential of very large eddy simulations (VLES) of flows dominated by (pseudo)-deterministic eddy structures, based on transient RANS (T-RANS) and similar approaches, is discussed and illustrated in an example of “ultra-hard” (very high Ra) thermal convection.

Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier

2009 ◽  
Vol 367 (1899) ◽  
pp. 2885-2903 ◽  
Author(s):  
Michael Leschziner ◽  
Ning Li ◽  
Fabrizio Tessicini
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Major Elements ◽  
Wall Layer ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Models ◽  
High Reynolds ◽  
Near Wall

This paper provides a discussion of several aspects of the construction of approaches that combine statistical (Reynolds-averaged Navier–Stokes, RANS) models with large eddy simulation (LES), with the objective of making LES an economically viable method for predicting complex, high Reynolds number turbulent flows. The first part provides a review of alternative approaches, highlighting their rationale and major elements. Next, two particular methods are introduced in greater detail: one based on coupling near-wall RANS models to the outer LES domain on a single contiguous mesh, and the other involving the application of the RANS and LES procedures on separate zones, the former confined to a thin near-wall layer. Examples for their performance are included for channel flow and, in the case of the zonal strategy, for three separated flows. Finally, a discussion of prospects is given, as viewed from the writer's perspective.

Approximation of attractors, large eddy simulations and multiscale methods

1991 ◽  
Vol 434 (1890) ◽  
pp. 23-39 ◽  
Keyword(s):  
Turbulent Flows ◽  
Mathematical Theory ◽  
Stokes Equations ◽  
Multiscale Methods ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Theory Approach ◽  
Navier Stokes Equations ◽  
Approximate Inertial Manifolds ◽  
Large Eddy

Recent advances in the mathematical theory of the Navier-Stokes equations have produced new insight in the mathematical theory of turbulence. In particular, the study of the attractor for the Navier-Stokes equations produced the first connection between two approaches to turbulence that seemed far apart, namely the conventional approach of Kolmogorov and the dynamical systems theory approach. Similarly the study of the approximation of the attractor in connection with the newly introduced concept of approximate inertial manifolds has produced a new approach to large eddy simulations and the study of the interaction of small and large eddies in turbulent flows. Our aim in this article is to survey and describe some of the new results concerning the functional properties of the Navier-Stokes equations and to discuss their relevance to turbulence.

Modeling Gravity and Turbidity Currents: Computational Approaches and Challenges

2015 ◽  
Vol 67 (4) ◽  
Author(s):  
Eckart Meiburg ◽  
Senthil Radhakrishnan ◽  
Mohamad Nasr-Azadani
Keyword(s):  
Conceptual Modeling ◽  
Review Article ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Turbidity Currents ◽  
New Developments ◽  
Box Models ◽  
Large Eddy ◽  
Gravity Driven ◽  
High Reynolds

In this review article, we discuss recent progress with regard to modeling gravity-driven, high Reynolds number currents, with the emphasis on depth-resolving, high-resolution simulations. The initial sections describe new developments in the conceptual modeling of such currents for the purpose of identifying the Froude number–current height relationship, in the spirit of the pioneering work by von Kármán and Benjamin. A brief introduction to depth-averaged approaches follows, including box models and shallow water equations. Subsequently, we provide a detailed review of depth-resolving modeling strategies, including direct numerical simulations (DNS), large-eddy simulations (LES), and Reynolds-averaged Navier–Stokes (RANS) simulations. The strengths and challenges associated with these respective approaches are discussed by highlighting representative computational results obtained in recent years.

scholarly journals Large eddy simulation of flows in industrial compressors: a path from 2015 to 2035

2014 ◽  
Vol 372 (2022) ◽  
pp. 20130323 ◽  
Author(s):  
N. Gourdain ◽  
F. Sicot ◽  
F. Duchaine ◽  
L. Gicquel
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Complex Geometry ◽  
Current Status ◽  
Navier Stokes ◽  
Future Research ◽  
Phase Lag ◽  
Eddy Simulation ◽  
Large Eddy ◽  
High Reynolds

A better understanding of turbulent unsteady flows is a necessary step towards a breakthrough in the design of modern compressors. Owing to high Reynolds numbers and very complex geometry, the flow that develops in such industrial machines is extremely hard to predict. At this time, the most popular method to simulate these flows is still based on a Reynolds-averaged Navier–Stokes approach. However, there is some evidence that this formalism is not accurate for these components, especially when a description of time-dependent turbulent flows is desired. With the increase in computing power, large eddy simulation (LES) emerges as a promising technique to improve both knowledge of complex physics and reliability of flow solver predictions. The objective of the paper is thus to give an overview of the current status of LES for industrial compressor flows as well as to propose future research axes regarding the use of LES for compressor design. While the use of wall-resolved LES for industrial multistage compressors at realistic Reynolds number should not be ready before 2035, some possibilities exist to reduce the cost of LES, such as wall modelling and the adaptation of the phase-lag condition. This paper also points out the necessity to combine LES to techniques able to tackle complex geometries. Indeed LES alone, i.e. without prior knowledge of such flows for grid construction or the prohibitive yet ideal use of fully homogeneous meshes to predict compressor flows, is quite limited today.

Flow and Heat Transfer in an Internally Ribbed Duct With Rotation: An Assessment of Large Eddy Simulations and Unsteady Reynolds-Averaged Navier-Stokes Simulations

2004 ◽  
Vol 127 (2) ◽  
pp. 306-320 ◽  
Author(s):  
A. K. Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Density Ratio ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Flow And Heat Transfer ◽  
Number Ratio ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

Large eddy simulations (LES) and unsteady Reynolds averaged Navier-Stokes (URANS) simulations have been performed for flow and heat transfer in a rotating ribbed duct. The ribs are oriented normal to the flow and arranged in a staggered configuration on the leading and trailing surfaces. The LES results are based on a higher-order accurate finite difference scheme with a dynamic Smagorinsky model for the subgrid stresses. The URANS procedure utilizes a two equation k-ε model for the turbulent stresses. Both Coriolis and centrifugal buoyancy effects are included in the simulations. The URANS computations have been carried out for a wide range of Reynolds number (Re=12,500-100,000), rotation number (Ro=0-0.5) and density ratio (Δρ∕ρ=0-0.5), while LES results are reported for a single Reynolds number of 12,500 without and with rotation (Ro=0.12,Δρ∕ρ=0.13). Comparison is made between the LES and URANS results, and the effects of various parameters on the flow field and surface heat transfer are explored. The LES results clearly reflect the importance of coherent structures in the flow, and the unsteady dynamics associated with these structures. The heat transfer results from both LES and URANS are found to be in reasonable agreement with measurements. LES is found to give higher heat transfer predictions (5–10% higher) than URANS. The Nusselt number ratio (Nu∕Nu0) is found to decrease with increasing Reynolds number on all walls, while they increase with the density ratio along the leading and trailing walls. The Nusselt number ratio on the trailing and sidewalls also increases with rotation. However, the leading wall Nusselt number ratio shows an initial decrease with rotation (till Ro=0.12) due to the stabilizing effect of rotation on the leading wall. However, beyond Ro=0.12, the Nusselt number ratio increases with rotation due to the importance of centrifugal-buoyancy at high rotation.

Non-equilibrium wall functions for large Eddy simulations of complex turbulent flows and heat transfer

2021 ◽  
Vol 88 ◽  
pp. 108758
Author(s):  
Yongxiang Li ◽  
Florian Ries ◽  
Wibke Leudesdorff ◽  
Kaushal Nishad ◽  
Andrea Pati ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Large Eddy Simulations ◽  
Wall Functions ◽  
Large Eddy ◽  
Non Equilibrium

Wall-resolved wavelet-based adaptive large-eddy simulation of bluff-body flows with variable thresholding

2016 ◽  
Vol 788 ◽  
pp. 303-336 ◽  
Author(s):  
Giuliano De Stefano ◽  
Alireza Nejadmalayeri ◽  
Oleg V. Vasilyev
Keyword(s):  
Turbulent Flows ◽  
Bluff Body ◽  
Large Eddy Simulations ◽  
Eddy Simulation ◽  
Computational Mesh ◽  
Large Eddy ◽  
High Reynolds ◽  
The One ◽  
Solid Obstacles ◽  
Bluff Body Flows

The wavelet-based eddy-capturing approach with variable thresholding is extended to bluff-body flows, where the obstacle geometry is enforced through Brinkman volume penalization. The use of a spatio-temporally varying threshold allows one to perform adaptive large-eddy simulations with the prescribed fidelity on a near optimal computational mesh. The space–time evolution of the threshold variable is achieved by solving a transport equation based on the Lagrangian path-line diffusive averaging methodology. The coupled wavelet-collocation/volume-penalization approach with variable thresholding is illustrated for a turbulent incompressible flow around an isolated stationary prism with square cross-section. Wavelet-based adaptive large-eddy simulations supplied with the one-equation localized dynamic kinetic energy-based model are successfully performed at moderately high Reynolds number. The present study demonstrates that the proposed variable thresholding methodology for wavelet-based modelling of turbulent flows around solid obstacles is feasible, accurate and efficient.

Random Flow Generation Technique for Large Eddy Simulations and Particle-Dynamics Modeling

2001 ◽  
Vol 123 (2) ◽  
pp. 359-371 ◽  
Author(s):  
A. Smirnov ◽  
S. Shi ◽  
I. Celik
Keyword(s):  
Turbulent Flows ◽  
Particle Tracking ◽  
Vector Fields ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Dynamics Modeling ◽  
Divergence Free Vector ◽  
Flow Generation ◽  
Large Eddy ◽  
Random Flow

A random flow generation (RFG) technique is presented, which can be used for initial/inlet boundary generation in LES (Large-Eddy-Simulations) or particle tracking in LES/RANS (Reynolds-Averaged Navier-Stokes) computations of turbulent flows. The technique is based on previous methods of synthesizing divergence-free vector fields from a sample of Fourier harmonics and allows to generate non-homogeneous anisotropic flow field representing turbulent velocity fluctuations. It was validated on the cases of boundary layer and flat plate flows. Applications of the technique to LES and particle tracking are considered.

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