The Use of Solution Adaptive Grid for Modeling Small Scale Turbulent Structures

2005 ◽  
Vol 127 (5) ◽  
pp. 936-944 ◽  
Author(s):  
G. de With ◽  
A. E. Holdø
Keyword(s):  
Flow Field ◽  
Turbulence Modeling ◽  
Flow Region ◽  
Adaptive Methods ◽  
Adaptive Grid ◽  
Small Scale ◽  
Free Shear Layer ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Computationally Intensive

The use of large eddy simulation (LES) is computationally intensive and various studies demonstrated the considerable range of vortex scales to be resolved in an LES type of simulation. The purpose of this study is to investigate the use of a dynamic grid adaptation (DGA) algorithm. Despite many developments related to adaptive methods and adaptive grid strategies, the use of DGA in the context of turbulence modeling is still not well understood, and various profound problems with DGA in relation to turbulence modeling are still present. The work presented in this paper focuses on the numerical modeling of flow around a circular cylinder in the sub-critical flow regime at a Reynolds number of 3.9∙103. LES simulations with conventional mesh and DGA have been performed with various mesh sizes, refinement criteria and re-meshing frequency, to investigate the effects of re-meshing on the flow field prediction. The results indicate that the turbulent flow field is sensitive to modifications in the mesh and re-meshing frequency, and it is suggested that the re-meshing in the unsteady flow region is affecting the onset of small scale flow motions in the free shear layer.

The Use of Solution Adaptive Grid for Modelling Small Scale Turbulent Structures

2004 ◽  
Author(s):  
G. de With ◽  
A. E. Holdo̸
Keyword(s):  
Flow Field ◽  
Flow Region ◽  
Adaptive Methods ◽  
Adaptive Grid ◽  
Turbulence Modelling ◽  
Small Scale ◽  
Free Shear Layer ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Computationally Intensive

The use of Large Eddy Simulation (LES) is computationally intensive and various studies demonstrated the considerable range of vortex scales to be resolved in an LES type of simulation. The purpose of this study is to investigate the use of a Dynamic Grid Adaptation (DGA) algorithm. Despite many developments related to adaptive methods and adaptive grid strategies, the use of DGA in the context of turbulence modelling is still not well understood, and various profound problems with DGA in relation to turbulence modelling are still present. The work presented in this paper focuses on the numerical modelling of flow around a circular cylinder in the sub-critical flow regime at a Reynolds number of 3.9·103. LES simulations with conventional mesh and DGA have been performed with various mesh sizes, refinement criteria and re-meshing frequency, to investigate the effects of re-meshing on the flow field prediction. The results indicate that the turbulent flow field is sensitive to modifications in the mesh and re-meshing frequency, and it is suggested that the remeshing in the unsteady flow region is affecting the onset of small scale flow motions in the free shear layer.

scholarly journals An Arbitrary Hybrid Turbulence Modeling Approach for Efficient and Accurate Automotive Aerodynamic Analysis and Design Optimization

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 407
Author(s):  
Saule Maulenkul ◽  
Kaiyrbek Yerzhanov ◽  
Azamat Kabidollayev ◽  
Bagdaulet Kamalov ◽  
Sagidolla Batay ◽  
...  
Keyword(s):  
Flow Field ◽  
Design Optimization ◽  
Automotive Industry ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Analysis And Design ◽  
Eddy Simulation ◽  
Gradient Based ◽  
Automotive Aerodynamics ◽  
Single Flow

The demand in solving complex turbulent fluid flows has been growing rapidly in the automotive industry for the last decade as engineers strive to design better vehicles to improve drag coefficients, noise levels and drivability. This paper presents the implementation of an arbitrary hybrid turbulence modeling (AHTM) approach in OpenFOAM for the efficient simulation of common automotive aerodynamics with unsteady turbulent separated flows such as the Kelvin–Helmholtz effect, which can also be used as an efficient part of aerodynamic design optimization (ADO) tools. This AHTM approach is based on the concept of Very Large Eddy Simulation (VLES), which can arbitrarily combine RANS, URANS, LES and DNS turbulence models in a single flow field depending on the local mesh refinement. As a result, the design engineer can take advantage of this unique and highly flexible approach to tailor his grid according to his design and resolution requirements in different areas of the flow field over the car body without sacrificing accuracy and efficiency at the same time. This paper presents the details of the implementation and careful validation of the AHTM method using the standard benchmark case of the Ahmed body, in comparison with some other existing models, such as RANS, URANS, DES and LES, which shows VLES to be the most accurate among the five examined. Furthermore, the results of this study demonstrate that the AHTM approach has the flexibility, efficiency and accuracy to be integrated with ADO tools for engineering design in the automotive industry. The approach can also be used for the detailed study of highly complex turbulent phenomena such as the Kelvin–Helmholtz instability commonly found in automotive aerodynamics. Currently, the AHTM implementation is being integrated with the DAFoam for gradient-based multi-point ADO using an efficient adjoint solver based on a Sparse Nonlinear optimizer (SNOPT).

scholarly journals A Study on the Instantaneous Turbulent Flow Field in a 90-Degree Elbow Pipe with Circular Section

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Shiming Wang ◽  
Cheng Ren ◽  
Yangfei Sun ◽  
Xingtuan Yang ◽  
Jiyuan Tu
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Flow Separation ◽  
Large Scale ◽  
Small Scale ◽  
Eddy Simulation ◽  
Dean Vortex ◽  
Instantaneous Flow Field ◽  
Instantaneous Pressure ◽  
Turbulent Flow Field

Based on the special application of 90-degree elbow pipe in the HTR-PM, the large eddy simulation was selected to calculate the instantaneous flow field in the 90-degree elbow pipe combining with the experimental results. The characteristics of the instantaneous turbulent flow field under the influence of flow separation and secondary flow were studied by analyzing the instantaneous pressure information at specific monitoring points and the instantaneous velocity field on the cross section of the elbow. The pattern and the intensity of the Dean vortex and the small scale eddies change over time and induce the asymmetry of the flow field. The turbulent disturbance upstream and the flow separation near the intrados couple with the vortexes of various scales. Energy is transferred from large scale eddies to small scale eddies and dissipated by the viscous stress in the end.

BEM Based Solution of Turbulent Flow Over Periodic Hills With Heat Transfer

2011 ◽  
Author(s):  
Leopold Sˇkerget ◽  
Jure Ravnik
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Small Scale ◽  
Test Case ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Turbulent Models

Detached turbulent flows are difficult to predict numerically and often serve as benchmark cases for developing new numerical schemes and new turbulent models. Turbulent flow over periodic hills is one such examples, since the flow exhibits separation and reattachment on a smoothly and/or sharp curved geometry, strong pressure gradients and fluctuation of the separation point in time. These cases have been chosen by many authors for testing different turbulence simulation approaches. When the bottom wall is heated, the complexity of the problem increased, since convective heat transfer is defined by small scale turbulent structures close to the wall. We developed a Reynolds-Averaged Navier-Stokes and Large Eddy Simulation solver based on the velocity-vorticity formulation of Navier Stokes equations. RANS equations are coupled by a low-Reynolds number turbulent model, while Smagorinsky subgrid model is used for LES. The governing equations are solved with a numerical solution algorithm, which is based on the boundary element method. The pressure field is computed in a post processing step by solving a Poisson equation. The single domain as well as domain decomposition approaches are applied. The developed method was validated using flow over periodic hills test case.

scholarly journals Explicit filtering to obtain grid-spacing-independent and discretization-order-independent large-eddy simulation of compressible single-phase flow

2012 ◽  
Vol 697 ◽  
pp. 399-435 ◽  
Author(s):  
Senthilkumaran Radhakrishnan ◽  
Josette Bellan
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Small Scale ◽  
Spatial Discretization ◽  
Grid Spacing ◽  
Eddy Simulation ◽  
Filter Width ◽  
Spacing Ratio ◽  
Large Eddy ◽  
Grid Independence

AbstractIn large-eddy simulation (LES), it is often assumed that the filter width is equal to the grid spacing. Predictions from such LES are grid-spacing dependent since any subgrid-scale (SGS) model used in the LES equations is dependent on the resolved flow field which itself varies with grid spacing. Moreover, numerical errors affect the flow field, especially the smallest resolved scales. Thus, predictions using this approach are affected by both modelling and numerical choices. However, grid-spacing-independent LES predictions unaffected by numerical choices are necessary to validate LES models through comparison with a trusted template. First, such a template is created here through direct numerical simulation (DNS). Then, simulations are conducted using the conventional LES equations and also LES equations which are here reformulated so that the small-scale-producing nonlinear terms in these equations are explicitly filtered (EF) to remove scales smaller than a fixed filter width; this formulation is called EFLES. First, LES is conducted with four SGS models, then EFLES is performed with two of the SGS models used in LES; the results from all these simulations are compared to those from DNS and from the filtered DNS (FDNS). The conventional LES solution is both grid-spacing and spatial discretization-order dependent, thus showing that both of these numerical aspects affect the flow prediction. The solution from the EFLES equations is grid independent for a high-order spatial discretization on all meshes tested. However, low-order discretizations require a finer mesh to reach grid independence. With an eighth-order discretization, a filter-width to grid-spacing ratio of two is sufficient to reach grid independence, while a filter-width to grid-spacing ratio of four is needed to reach grid independence when a fourth- or a sixth-order discretization is employed. On a grid fine enough to be utilized in a DNS, the EFLES solution exhibits grid independence and does not converge to the DNS solution. The velocity-fluctuation spectra of EFLES follow those of FDNS independent of the grid spacing used, in concert with the original concept of LES. The reasons for the different predictions of conventional LES or EFLES according to the SGS model used, and the different characteristics of the EFLES predictions compared to those from conventional LES are analysed.

scholarly journals A new downscaling method for sub-grid turbulence modeling

2017 ◽  
Vol 17 (11) ◽  
pp. 6531-6546
Author(s):  
Lucie Rottner ◽  
Christophe Baehr ◽  
Fleur Couvreux ◽  
Guylaine Canut ◽  
Thomas Rieutord
Keyword(s):  
High Resolution ◽  
Turbulence Modeling ◽  
Particle System ◽  
Numerical Models ◽  
Particle Systems ◽  
Small Scale ◽  
Grid Turbulence ◽  
Turbulent Structures ◽  
High Resolution Data ◽  
Scale Turbulence

Abstract. In this study we explore a new way to model sub-grid turbulence using particle systems. The ability of particle systems to model small-scale turbulence is evaluated using high-resolution numerical simulations. These high-resolution data are averaged to produce a coarse-grid velocity field, which is then used to drive a complete particle-system-based downscaling. Wind fluctuations and turbulent kinetic energy are compared between the particle simulations and the high-resolution simulation. Despite the simplicity of the physical model used to drive the particles, the results show that the particle system is able to represent the average field. It is shown that this system is able to reproduce much finer turbulent structures than the numerical high-resolution simulations. In addition, this study provides an estimate of the effective spatial and temporal resolution of the numerical models. This highlights the need for higher-resolution simulations in order to evaluate the very fine turbulent structures predicted by the particle systems. Finally, a study of the influence of the forcing scale on the particle system is presented.

Numerical Investigation of Flow Around a Multi-Element Airfoil with Hybrid RANS-LES Approaches Based on SST Model

2017 ◽  
Vol 34 (2) ◽  
pp. 123-134 ◽  
Author(s):  
L. Zhang ◽  
J. Li ◽  
Y. F. Mou ◽  
H. Zhang ◽  
W. B. Shi ◽  
...  
Keyword(s):  
Turbulence Modeling ◽  
Experimental Result ◽  
Numerical Dissipation ◽  
Small Scale ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Third Order ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

AbstractAccurate prediction of the flow around multi-element airfoil is a prerequisite for improving aerodynamic performance, but its complex flow features impose high demands on turbulence modeling. In this work, delayed detached-eddy-simulation (DDES) and zonal detached-eddy-simulation (ZDES) was applied to simulate the flow past a three-element airfoil. To investigate the effects of numerical dissipation of spatial schemes, the third-order MUSCL and the fifth-order interpolation based on modified Roe scheme were implemented. From the comparisons between the calculations and the available experimental result, third-order MUSCL-Roe can provide satisfactory mean velocity profiles, but the excessive dissipation suppresses the velocity fluctuations level and eliminates the small-scale structures; DDES cannot reproduce the separation near the trailing edge of the flap which lead to the discrepancy in mean pressure coefficients, while ZDES result has better tally with the experiment.

scholarly journals A new downscaling method for sub-grid turbulence modeling

2016 ◽  
Author(s):  
L. Rottner ◽  
C. Baehr ◽  
F. Couvreux ◽  
G. Canut ◽  
T. Rieutord
Keyword(s):  
High Resolution ◽  
Turbulence Modeling ◽  
Particle System ◽  
Numerical Models ◽  
Atmospheric Model ◽  
Particle Systems ◽  
Small Scale ◽  
Grid Turbulence ◽  
Turbulent Structures ◽  
Scale Turbulence

Abstract. In this study we explore a new way to model sub-grid turbulence using particle systems. The ability of particle systems to model small scale turbulence is evaluated using high resolution numerical simulations. These high-resolution simulations have been performed with the research atmospheric model Meso-NH and averaged at larger scale from which a complete downscaling experience, via a particle system, have been performed. The particle simulations are compared to the high-resolution simulation for the representation of the wind fluctuations and the turbulent kinetic energy. Despite the simplicity of the physical model used to drive the particles, the results show that particle system is able to represent the average field. It is shown that this system is able to reproduce much finer turbulent structures than the numerical high-resolution simulations. In addition, this study provides an estimate of the effective spatial and temporal resolution of the numerical models. This highlights the need for higher resolution simulations to be able to evaluate the very fine turbulent structures predicted by the particle systems. Eventually a study of the influence of the forcing scale on the particle system is presented.

Turbulence Modeling for the Numerical Simulation of Film and Effusion Cooling Flows

2007 ◽  
Author(s):  
Alessandro Bacci ◽  
Bruno Facchini
Keyword(s):  
Numerical Simulation ◽  
Film Cooling ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Cooling Flows ◽  
Eddy Simulation ◽  
Viscosity Models ◽  
Rans Turbulence Models ◽  
Computationally Intensive

RANS simulations are known to suffer from serious deficiencies in the prediction of jet in a crossflow (JCF) because of the high complexity of this kind of flow. Particularly, the coherent structures resulting from the interaction of the two flow streams are characterized by a highly unsteady and anisotropic behavior which hardly stresses the hypotheses underling common eddy viscosity models (EVMs). Direct numerical simulation (DNS) and large eddy simulation (LES) methodologies are still excessively computationally intensive to be used as ordinary design tools. Therefore, the development of reliable RANS turbulence models for film cooling flows deserved a great deal of attention from the gas turbine community. Computations presented in this work were carried out using a modified k-ε turbulence model specifically designed for film cooling flows. The model, due to Lakehal et al., is based on the usage of an anisotropic eddy viscosity. The model has been implemented in the framework of a CFD commercial package through the user subroutine features. Computational model is developed following the suggestions of Walters and Leylek concerning the correct representation of the problem geometry and the location of the boundary conditions. The predictive capabilities of the model concerning the ability to capture the main flow structures as well as heat transfer features are investigated. Comparison of computed adiabatic effectiveness profiles with experimental measurements is provided in order to quantitatively validate the model. Results obtained with standard EVMs, particularly a two layer standard k-ε model, are also shown in order to reveal the improvements in the predictive capabilities resulting from the modified models.

Turbulence Modeling for Thrust Reverser Flow Field Prediction Methods

1992 ◽  
Author(s):  
Robert E. Childs ◽  
Laura C. Rodman ◽  
Peter Bradshaw
Keyword(s):  
Flow Field ◽  
Turbulence Modeling ◽  
Prediction Methods ◽  
Thrust Reverser
Sign in / Sign up

Export Citation Format

Share Document