Hybrid LES Approach for Practical Turbomachinery Flows—Part I: Hierarchy and Example Simulations

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Paul Tucker ◽  
Simon Eastwood ◽  
Christian Klostermeier ◽  
Richard Jefferson-Loveday ◽  
James Tyacke ◽  
...  
Keyword(s):  
Convex Surface ◽  
Computational Cost ◽  
Companion Paper ◽  
Navier Stokes ◽  
Computationally Efficient ◽  
Turbulent Structures ◽  
Hybrid Strategy ◽  
Eddy Simulation ◽  
Related Approach ◽  
Les Model

Unlike Reynolds-averaged Navier–Stokes (RANS) models that need calibration for different flow classes, LES (where larger turbulent structures are resolved by the grid and smaller modeled in a fashion reminiscent of RANS) offers the opportunity to resolve geometry dependent turbulence as found in complex internal flows—albeit at substantially higher computational cost. Based on the results for a broad range of studies involving different numerical schemes, large eddy simulation (LES) models and grid topologies, an LES hierarchy and hybrid LES related approach is proposed. With the latter, away from walls, no LES model is used, giving what can be termed numerical LES (NLES). This is relatively computationally efficient and makes use of the dissipation present in practical industrial computational fluid dynamics (CFD) programs. Near walls, RANS modeling is used to cover over numerous small structures, the LES resolution of which is generally intractable with current computational power. The linking of the RANS and NLES zones through a Hamilton–Jacobi equation is advocated. The RANS-NLES hybridization makes further sense for compressible flow solvers, where, as the Mach number tends to zero at walls, excessive dissipation can occur. The hybrid strategy is used to predict flow over a rib roughened surface and a jet impinging on a convex surface. These cases are important for blade cooling and show encouraging results. Further results are presented in a companion paper.

Hybrid LES Approach for Practical Turbomachinery Flows: Part 1—Hierarchy and Example Simulations

2010 ◽  
Author(s):  
Paul Tucker ◽  
Simon Eastwood ◽  
Christian Klostermeier ◽  
Richard Jefferson-Loveday ◽  
James Tyacke ◽  
...  
Keyword(s):  
Convex Surface ◽  
Computational Cost ◽  
Companion Paper ◽  
Navier Stokes ◽  
Computationally Efficient ◽  
Turbulent Structures ◽  
Hybrid Strategy ◽  
Related Approach ◽  
Rans Models ◽  
Les Model

Unlike Reynolds Averaged Navier Stokes (RANS) models which need calibration for different flow classes, LES (where larger turbulent structures are resolved by the grid and smaller modeled in a fashion reminiscent of RANS) offers the opportunity to resolve geometry dependent turbulence as found in complex internal flows — albeit at substantially higher computational cost. Based on the results for a broad range of studies involving different numerical schemes, LES models and grid topologies an LES hierarchy and hybrid LES related approach is proposed. With the latter, away from walls, no LES model is used, giving what can be termed Numerical LES (NLES). This is relatively computationally efficient and makes use of the dissipation present in practical industrial CFD programs. Near walls, RANS modeling is used to cover over numerous small structures, the LES resolution of which is generally intractable with current computational power. The linking of the RANS and NLES zones through a Hamilton-Jacobi equation is advocated. The RANS-NLES hybridization makes further sense for compressible flow solvers, where, as the Mach number tends to zero at walls, excessive dissipation can occur. The hybrid strategy is used to predict flow over a rib roughened surface and a jet impinging on a convex surface. These cases are important for blade cooling and show encouraging results. Further results are presented in a companion paper.

Hybrid LES Approach for Practical Turbomachinery Flows—Part II: Further Applications

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Paul Tucker ◽  
Simon Eastwood ◽  
Christian Klostermeier ◽  
Hao Xia ◽  
Prasun Ray ◽  
...  
Keyword(s):  
Navier Stokes ◽  
Jet Flows ◽  
Hybrid Strategy ◽  
Eddy Simulation ◽  
Wall Flows ◽  
Large Eddy ◽  
Blade Section ◽  
Transition Modeling ◽  
Fan Blade ◽  
Les Model

A hybrid large eddy simulation (LES) related technique is used to explore some key turbomachinery relevant flows. Near wall Reynolds-averaged Navier-Stokes (RANS) modeling is used to cover over especially small scales, the LES resolution of which is generally intractable with current computational power. Away from walls, large eddy type simulation is used but with no LES model (numerical LES (NLES)). Linking of the two model zones through a Hamilton–Jacobi equation is explored. The hybrid strategy is used to predict turbine and compressor end wall flows, flow around a fan blade section, jet flows, and a cutback trailing edge. Also, application of NLES to the flow in an idealized high pressure compressor drum cavity is considered. Generally, encouraging results are found. However, challenges remain, especially for flows where transition modeling is important.

scholarly journals Effect of Local Turbulent Structures on the Hot Jet in Transitional Flow

2021 ◽  
Vol 2119 (1) ◽  
pp. 012009
Author(s):  
A Sakhnov ◽  
V V Lukashov
Keyword(s):  
Stokes Equations ◽  
Flow Direction ◽  
Transitional Flow ◽  
Navier Stokes ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Eddy Viscosity Model ◽  
Air Jet ◽  
Open Volume ◽  
Subgrid Scales

Abstract Turbulent parts localized in flow direction may arise in a pipe with transitional regime of the stable laminar Poiseuille flow. A key condition for occurrence of such structures is a pipe with rather long length relative to its diameter. Our paper presents numerical modelling of the hot air jet flowing from the long pipe into the cold open volume at Re=2426. The modelling was performed in OpenFOAM software on the basis of the large eddy simulation (LES) method. The WALE (Wall-adapting local eddy-viscosity) model was used for closure of Navier-Stokes equations on subgrid scales. We demonstrated that local turbulent structures have a weak effect on the hot jet at flowing into the cold open volume.

scholarly journals LES and RANS Investigations Into Buoyancy-Affected Convection in a Rotating Cavity With a Central Axial Throughflow

2006 ◽  
Author(s):  
Zixiang Sun ◽  
Klas Lindblad ◽  
John W. Chew ◽  
Colin Young
Keyword(s):  
Heat Transfer ◽  
Tangential Velocity ◽  
Navier Stokes ◽  
Test Cases ◽  
Test Rig ◽  
Rotating Disc ◽  
Eddy Simulation ◽  
Rotating Cavity ◽  
Large Eddy ◽  
Les Model

The buoyancy-affected flow in rotating disc cavities, such as occurs in compressor disc stacks, is known to be complex and difficult to predict. In the present work large eddy simulation (LES) and unsteady Reynolds-averaged Navier-Stokes (RANS) solutions are compared with other workers’ measurements from an engine representative test rig. The Smagorinsky-Lilly model was employed in the LES simulations, and the RNG k-ε turbulence model was used in the RANS modelling. Three test cases were investigated in a range of Grashof number Gr = 1.87 to 7.41×108 and buoyancy number Bo = 1.65 to 11.5. Consistent with experimental observation, strong unsteadiness was clearly observed in the results of both models, however the LES results exhibited a finer flow structure than the RANS solution. The LES model also achieved significantly better agreement with velocity and heat transfer measurements than the RANS model. Also, temperature contours obtained from the LES results have a finer structure than the tangential velocity contours. Based on the results obtained in this work, further application of LES to flows of industrial complexity is recommended.

Wind-Driven Natural Ventilation in an Areaway-Attached Basement with a Single-Sided Opening for Residential Purposes

2011 ◽  
Vol 383-390 ◽  
pp. 5344-5349
Author(s):  
Zhen Bu
Keyword(s):  
Natural Ventilation ◽  
Ventilation Rate ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Effective Ventilation ◽  
The Mean ◽  
Ventilation Rates ◽  
Les Model ◽  
Good Agreement

This paper discusses the sustainability of the areaway-attached basement concept with the attentions focused on wind-driven single-sided natural ventilation. First, numerical simulations were performed on an areaway-attached basement with a single-sided opening. Two CFD approaches: Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) were used and compared with the previous experimental results of effective ventilation rate. A good agreement between the measurement and LES model was found and RANS model tends to underestimate the ventilation rates. Furthermore, Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement was investigated for different wind incidence angles to examine the influences of wind direction on ventilation performances.

On the Investigation of Flow around the Square Cylinder Based on Different LES Models

2012 ◽  
Vol 594-597 ◽  
pp. 2676-2679
Author(s):  
Zhe Liu
Keyword(s):  
Flow Characteristics ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Square Cylinder ◽  
Rans Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Les Model

Although the conventional Reynolds-averaged Navier–Stokes (RANS) model has been widely applied in the industrial and engineering field, it is worthwhile to study whether these models are suitable to investigate the flow filed varying with the time. With the development of turbulence models, the unsteady Reynolds-averaged Navier–Stokes (URANS) model, detached eddy simulation (DES) and large eddy simulation (LES) compensate the disadvantage of RANS model. This paper mainly presents the theory of standard LES model, LES dynamic model and wall-adapting local eddy-viscosity (WALE) LES model. And the square cylinder is selected as the research target to study the flow characteristics around it at Reynolds number 13,000. The influence of different LES models on the flow field around the square cylinder is compared.

scholarly journals The Collection Efficiency of Shielded and Unshielded Precipitation Gauges. Part II: Modeling Particle Trajectories

2015 ◽  
Vol 17 (1) ◽  
pp. 245-255 ◽  
Author(s):  
Matteo Colli ◽  
Luca G. Lanza ◽  
Roy Rasmussen ◽  
Julie M. Thériault
Keyword(s):  
Collection Efficiency ◽  
Time Dependent ◽  
Navier Stokes ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Efficiency Comparison ◽  
The One ◽  
The Impact

Abstract The use of windshields to reduce the impact of wind on snow measurements is common. This paper investigates the catching performance of shielded and unshielded gauges using numerical simulations. In Part II, the role of the windshield and gauge aerodynamics, as well as the varying flow field due to the turbulence generated by the shield–gauge configuration, in reducing the catch efficiency is investigated. This builds on the computational fluid dynamics results obtained in Part I, where the airflow patterns in the proximity of an unshielded and single Alter shielded Geonor T-200B gauge are obtained using both time-independent [Reynolds-averaged Navier–Stokes (RANS)] and time-dependent [large-eddy simulation (LES)] approaches. A Lagrangian trajectory model is used to track different types of snowflakes (wet and dry snow) and to assess the variation of the resulting gauge catching performance with the wind speed. The collection efficiency obtained with the LES approach is generally lower than the one obtained with the RANS approach. This is because of the impact of the LES-resolved turbulence above the gauge orifice rim. The comparison between the collection efficiency values obtained in case of shielded and unshielded gauge validates the choice of installing a single Alter shield in a windy environment. However, time-dependent simulations show that the propagating turbulent structures produced by the aerodynamic response of the upwind single Alter blades have an impact on the collection efficiency. Comparison with field observations provides the validation background for the model results.

scholarly journals Investigation of flow structures in a turbulent separating flow using hybrid RANS-LES model

2017 ◽  
Vol 27 (7) ◽  
pp. 1430-1450 ◽  
Author(s):  
Gaurav Kumar ◽  
Ashoke De ◽  
Harish Gopalan
Keyword(s):  
Computational Cost ◽  
Model Performance ◽  
Flow Fields ◽  
Navier Stokes ◽  
Content Type ◽  
Practical Applications ◽  
Instantaneous Flow ◽  
Separating Flow ◽  
Similar Accuracy ◽  
Les Model

Purpose Hybrid Reynolds-averaged Navier–Stokes large eddy simulation (RANS-LES) methods have become popular for simulation of massively separated flows at high Reynolds numbers due to their reduced computational cost and good accuracy. The current study aims to examine the performance of LES and hybrid RANS-LES model for a given grid resolution. Design/methodology/approach For better assessment and contrast of model performance, both mean and instantaneous flow fields have been investigated. For studying instantaneous flow, proper orthogonal decomposition has been used. Findings Current analysis shows that hybrid RANS-LES is capable of achieving similar accuracy in prediction of both mean and instantaneous flow fields at a very coarse grid as compared to LES. Originality/value Focusing mostly on the practical applications of computation, most of the attention has been given to the prediction of one-point flow statistics and little consideration has been put to two-point statistics. Here, two-point statistics has been considered using POD to investigate unsteady turbulent flow.

Large Eddy Simulation of Aerodynamic Forces on a Bridge Pylon

2011 ◽  
Vol 243-249 ◽  
pp. 1578-1582
Author(s):  
Xu Yong Ying ◽  
Fu You Xu ◽  
Zhe Zhang ◽  
Yong Gang Tan
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Wind Tunnel Test ◽  
Navier Stokes ◽  
Aerodynamic Forces ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

In this study, aerodynamic forces on a bridge pylon are investigated by three-dimensional computational fluid dynamics using Large eddy simulation (LES) technology. The main objective is to identify the wind load parameters of the pylon and examine the accuracy of LES model applied to the bluff-body flows. The numerical results were compared with the available wind tunnel test results. Also, a comparison between using LES and Reynolds averaged Navier-Stokes equations with the RNG model have been made. It is found that the LES model competes the RNG model in accuracy for predictions of aerodynamic forces on the pylon.

Evaluation of Performance and Code-to-Code Variation of a Dynamic Hybrid RANS/LES Model for Simulation of Backward-Facing Step Flow

2018 ◽  
Author(s):  
Olalekan O. Shobayo ◽  
D. Keith Walters
Keyword(s):  
Cfd Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Test Case ◽  
Mean Flow ◽  
Backward Facing Step ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Dynamic Hybrid ◽  
Les Model

Computational fluid dynamics (CFD) simulation results are presented for the canonical test case of flow over a backward facing step (BFS). The BFS case exhibits complex physics including turbulent separation, reattachment, and boundary layer restart. Results are obtained using two different turbulence models as representative examples of two classes of modeling: Reynolds-averaged Navier-Stokes (RANS) and hybrid RANS-LES (large-eddy simulation). The specific models used are k-ω SST and dynamic hybrid RANS-LES (DHRL). The objective of the study is to compare the performance of both turbulence models as implemented in three different flow solvers (Flow Psi, Loci-CHEM, and Ansys FLUENT) and using three different methods for numerical discretization of the convective terms in the governing equations. Results are compared to experimental data for validation purposes. Results show that both k-ω SST and DHRL models are capable of reproducing the mean flow physics with reasonable accuracy. The differences due to solver algorithm and convective discretization scheme are apparent for both models, but the DHRL model shows more sensitivity, as expected. Overall the results highlight the importance of considering all integrated aspects of a turbulent CFD simulation to ensure that an optimum combination of model and numerical method are employed.

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