Comparison of LES of Steady Transitional Flow in an Idealized Stenosed Axisymmetric Artery Model With a RANS Transitional Model

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
F. P. P. Tan ◽  
N. B. Wood ◽  
G. Tabor ◽  
X. Y. Xu
Keyword(s):  
Experimental Data ◽  
Turbulence Intensity ◽  
Eddy Viscosity ◽  
Flow Analysis ◽  
Wall Turbulence ◽  
Transitional Flow ◽  
Navier Stokes ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Accurate Treatment

In this study, two different turbulence methodologies are investigated to predict transitional flow in a 75% stenosed axisymmetric experimental arterial model and in a slightly modified version of the model with an eccentric stenosis. Large eddy simulation (LES) and Reynolds-averaged Navier–Stokes (RANS) methods were applied; in the LES simulations eddy viscosity subgrid-scale models were employed (basic and dynamic Smagorinsky) while the RANS method involved the correlation-based transitional version of the hybrid k-ε/k-ω flow model. The RANS simulations used 410,000 and 820,000 element meshes for the axisymmetric and eccentric stenoses, respectively, with y+ less than 2 viscous wall units for the boundary elements, while the LES used 1,200,000 elements with y+ less than 1. Implicit filtering was used for LES, giving an overlap between the resolved and modeled eddies, ensuring accurate treatment of near wall turbulence structures. Flow analysis was carried out in terms of vorticity and eddy viscosity magnitudes, velocity, and turbulence intensity profiles and the results were compared both with established experimental data and with available direct numerical simulations (DNSs) from the literature. The simulation results demonstrated that the dynamic Smagorinsky LES and RANS transitional model predicted fairly comparable velocity and turbulence intensity profiles with the experimental data, although the dynamic Smagorinsky model gave the best overall agreement. The present study demonstrated the power of LES methods, although they were computationally more costly, and added further evidence of the promise of the RANS transition model used here, previously tested in pulsatile flow on a similar model. Both dynamic Smagorinsky LES and the RANS model captured the complex transition phenomena under physiological Reynolds numbers in steady flow, including separation and reattachment. In this respect, LES with dynamic Smagorinsky appeared more successful than DNS in replicating the axisymmetric experimental results, although inflow conditions, which are subject to caveats, may have differed. For the eccentric stenosis, LES with Smagorinsky coefficient of 0.13 gave the closest agreement with DNS despite the known shortcomings of fixed coefficients. The relaminarization as the flow escaped the influence of the stenosis was amply demonstrated in the simulations, graphically so in the case of LES.

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.

Reliable and Accurate Prediction of Three-Dimensional Separation in Asymmetric Diffusers Using Large-Eddy Simulation

2009 ◽  
Author(s):  
Hayder Schneider ◽  
Dominic von Terzi ◽  
Hans-Jo¨rg Bauer ◽  
Wolfgang Rodi
Keyword(s):  
Experimental Data ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

Reynolds-Averaged Navier-Stokes (RANS) calculations and Large-Eddy Simulations (LES) of the flow in two asymmetric three-dimensional diffusers were performed. The numerical setup was chosen to be in compliance with previous experiments. The aim of the present study is to find the least expensive method to compute reliably and accurately the impact of geometric sensitivity on the flow. RANS calculations fail to predict both the extent and location of the three-dimensional separation bubble. In contrast, LES is able to determine the amount of reverse flow and the pressure coefficient within the accuracy of experimental data.

Prediction of Aeroacoustic Resonance in Cavities of Hole-Pattern Stator Seals

2010 ◽  
Author(s):  
David N. Liliedahl ◽  
Forrest L. Carpenter ◽  
Paul G. A. Cizmas
Keyword(s):  
Experimental Data ◽  
Flow Instability ◽  
Numerical Results ◽  
Navier Stokes ◽  
Empirical Constant ◽  
Freestream Velocity ◽  
Flow Solver ◽  
Eddy Simulation ◽  
Flow Past ◽  
Acoustic Instabilities

A Reynolds-averaged Navier-Stokes (RANS) solver developed in-house was used to simulate grazing channel flow past single and multiple cavities. The objective of this investigation was to predict fluid instabilities in hole-pattern stator seals. The numerical results generated with the RANS solver showed good agreement with those obtained using a commercial Large Eddy Simulation (LES) code. In addition, the numerical results agreed well with experimental data. Rossiter’s formula, a popular semi-empirical model used to predict frequencies of hole-tone acoustic instabilities caused by grazing fluid flow past open cavities, was modified using the RANS solver results to allow for its application to channel flows. This was done by modifying the empirical constant κ, the ratio of vortex velocity and the freestream velocity. The dominant frequencies predicted using the Rossiter’s formula with the new κ value matched well the experimental data for hole-pattern stator seals. The RANS solver accurately captured the salient features of the flow/acoustic interaction and predicted well the dominant acoustic frequencies measured in an experimental investigation. The flow solver also provided detailed physical insight into the cavity flow instability mechanism.

Comparison of Partially Averaged Navier–Stokes and Large-Eddy Simulations of the Flow Around a Cuboid Influenced by Crosswind

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Siniša Krajnović ◽  
Per Ringqvist ◽  
Branislav Basara
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Better Than ◽  
Good Agreement ◽  
Near Wall

The paper presents a partially averaged Navier–Stokes (PANS) simulation of the flow around a cuboid influenced by crosswind. The results of the PANS prediction are validated against experimental data and results of a large-eddy simulation (LES) made using the same numerical conditions as PANS. The PANS shows good agreement with the experimental data. The prediction of PANS was found to be better than that of the LES in flow regions where simulations suffered from poor near-wall resolution.

scholarly journals Jet Noise in Airframe Integration and Shielding

2020 ◽  
Vol 10 (2) ◽  
pp. 511
Author(s):  
Saman Salehian ◽  
Reda Mankbadi
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Jet Noise ◽  
Numerical Approach ◽  
Navier Stokes ◽  
Complex Geometries ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

This paper reviews and presents new results on the effect of airframe integration and shielding on jet noise. Available experimental data on integration effects are analyzed. The available options for the computation of jet noise are discussed, and a practical numerical approach for the present topic is recommended. Here, it is demonstrated how a hybrid large eddy simulation—unsteady Reynolds-averaged Navier-Stokes approach can be implemented to simulate the effect of shielding on radiated jet noise. This approach provides results consistent with the experiment and suggests a framework for studying more complex geometries involving airframe integration effects.

Some Observations on the Computational Sensitivity of Rotating Cavity Flows

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Tom Hickling ◽  
Li He
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Systematic Investigation ◽  
Navier Stokes ◽  
Cavity Flows ◽  
Detached Eddy Simulation ◽  
Bulk Fluid ◽  
Eddy Simulation ◽  
Rotating Cavity ◽  
Large Eddy

Abstract Across the open literature, there is no clear consensus on what the most suitable modeling fidelity is for rotating cavity flows. Although it is a widely held opinion that unsteady Reynolds-averaged-Navier–Stokes (URANS) approaches are unsuitable, many authors have succeeded in getting reasonable heat transfer results with them. There is also a lack of research into the validity of hybrid URANS/large eddy simulation (LES) type approaches such as detached eddy simulation (DES). This paper addresses these research challenges with a systematic investigation of a rotating cavity with axial throughflow at Grashof numbers of 3.03×109 and 3.03×1011. The disk near-wall layers remained laminar at both conditions, meaning that a turbulence model should not be active in these regions. The disk heat transfer was observed to affect the near-disk aerodynamics, which in turn affect the disk heat transfer: this feedback loop implies that conjugate heat transfer computations of rotating cavities may be worth investigating. On the shroud, additional eddy viscosity in URANS and DES was found to interfere with the formation of heat transfer enhancing streaks, whilst these were always captured by LES. DES exhibited a concerning behavior at the higher Grashof number. Locally generated eddy viscosity from the shroud was injected into the bulk fluid by the radial inflow. This contaminated the entire cavity with nonphysical modeled turbulence. As the radial inflow is a characteristic feature of rotating cavity flows, these results show that caution is necessary when applying hybrid URANS/LES approaches to this type of flow.

Application of a Transition-Sensitive Two-Equation Turbulence Model to CFD Simulations of Missile Nose-Cone Geometries

2007 ◽  
Author(s):  
J. M. Jones ◽  
D. K. Walters
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Transitional Flow ◽  
Test Cases ◽  
Freestream Turbulence ◽  
Model Framework ◽  
Modeling Framework ◽  
Flow Solver ◽  
New Model

This paper presents results from an ongoing effort to develop and validate a two-equation eddy-viscosity turbulence model for computational fluid dynamics (CFD) prediction of transitional and turbulent flow. The new model is based on a k-ω model framework, making it more easily implemented into existing general-purpose CFD solvers than other recently proposed model forms. The model incorporates inviscid and viscous damping functions for the eddy viscosity, as well as a production damping term, in order to reproduce the appropriate effects of laminar, transitional, and turbulent boundary layer flow. The new model has been implemented into a Mississippi State University (MSU) Computational Simulation and Design Center (SimCenter) developed flow solver (U2NCLE), as well as a commercially available CFD code (FLUENT). For model validation, comparisons were made to experimental data for an incompressible, zero-pressure gradient, flat plate geometry over a range of freestream turbulence quantities, using both of the flow solvers. Additional test cases were performed with the in-house flow solver and compared to experimental data for two sharp-cone geometries. The Mach number for the cone cases ranged from 0.4 to 2. The results presented in this document show that the new model performed well for the 2-D test cases and showed agreement with the experimental data of the 3-D geometries. The results illustrate the ability of the model to yield reasonable predictions of transitional flow behavior using a very simple modeling framework, including an appropriate response to freestream turbulence quantities.

Computation of Three-Dimensional Compressible Flow From a Rectangular Nozzle With Delta Tabs

1999 ◽  
Vol 121 (2) ◽  
pp. 235-242 ◽  
Author(s):  
D. R. Reddy ◽  
C. J. Steffen ◽  
K. B. M. Q. Zaman
Keyword(s):  
Experimental Data ◽  
Nozzle Exit ◽  
Flow Analysis ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Navier Stokes ◽  
Rectangular Nozzle ◽  
Flow Configurations ◽  
Subsonic Jet

A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier-Stokes code for a 3:1 rectangular nozzle with two delta tabs located at the nozzle exit plane to enhance mixing. Two flow configurations, a subsonic jet case and a supersonic jet case using the same tab configuration, which were previously studied experimentally, are computed and compared with the experimental data. The experimental data include streamwise velocity and vorticity distributions for the subsonic case, and Mach number distributions for the supersonic case, at various axial locations downstream of the nozzle exit. The computational results show very good agreement with the experimental data. In addition, the effect of compressibility on vorticity dynamics is examined by comparing the vorticity contours of the subsonic jet case with those of the supersonic jet case which were not measured in the experiment.

An Aerodynamic Investigation of an Isolated Stationary Formula 1 Wheel Assembly

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
John Axerio-Cilies ◽  
Emin Issakhanian ◽  
Juan Jimenez ◽  
Gianluca Iaccarino
Keyword(s):  
Experimental Data ◽  
Large Scale ◽  
Turbulence Modeling ◽  
Cross Flow ◽  
Vortex Pair ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Flow Features ◽  
Large Scale Flow ◽  
Flow Blockage

The flowfield around a 60% scale stationary Formula 1 tire in contact with the ground in a closed wind tunnel at a Reynolds number of 500,000 was computationally examined in order to assess the accuracy of different turbulence modeling techniques and confirm the existence of large scale flow features. A simplified and replica tire model that includes all brake components was tested to determine the sensitivity of the wake to cross flow within the tire hub along with the flow blockage caused by the brake assembly. The results of steady and unsteady Reynolds averaged Navier-Stokes (URANS) equations and a large eddy simulation (LES) were compared with the experimental data. The LES closure and the RANS closure that accounted for unsteadiness with low eddy viscosity (unsteady kω-SST) matched closest to the experimental data both in point wise velocity comparisons along with location and intensity of the strong counter-rotating vortex pair dominating the far wake of the tire.

Development and Validation of Computational Fluid Dynamics Models for Initial Stages of Cavitation

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Eduard Amromin
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Cavitating Flows ◽  
Cavitation Inception ◽  
Eddy Simulation ◽  
Cfd Models ◽  
Liquid Flows

Various computational fluid dynamics (CFD) models employed for cavitating flows are substantially based on semi-empirical assumptions about cavitation forms and liquid flows around cavitating bodies. Therefore, the model applicability must be validated with experimental data. The stages of validation of the models are analyzed here with data on cavitating hydrofoils and axisymmetric bodies in water. Results of Reynolds-averaged Navier–Stokes (RANS), large-eddy simulation (LES), detached-eddy simulation (DES), and viscous-inviscid interaction methods are compared. The necessity of simultaneous validation of several flow parameters (as cavitation inception number and location of the appearing cavity) is pointed out. Typical uncertainties in water tunnel model test data (water quality, simplified account of wall effect) and possibilities to take them into account are also discussed. The provided comparison with experimental data manifests the impossibility to describe initial stages of cavitating flows using any single model and importance of employment of a combination of models for both the cavitation zones and the flow outside of cavities.

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