Large Eddy Simulation of the Compressible Flow Over an Open Cavity

2002 ◽  
Author(s):  
Keon-Je Oh ◽  
Tim Colonius
Keyword(s):  
Large Eddy Simulation ◽  
Shear Layer ◽  
Dynamic Model ◽  
Compressible Flow ◽  
Stokes Equations ◽  
Open Cavity ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Model Coefficient

Large eddy simulation is used to investigate the compressible flow over a open cavity. The sub-grid scale stresses are modeled using the dynamic model. The compressible Navier-Stokes equations are solved with the sixth order accurate compact finite difference scheme in the space and the 4th order Runge-Kutta scheme in the time. The buffer zone techniques are used for non-reflecting boundary conditions. The results show a typical flow pattern of the shear layer mode of oscillation over the cavity. The votical disturbances, the roll-up of vorticity, and impingement and scattering of vorticity at the downstream cavity edge can be seen in the shear layer, while the flow inside the cavity is relatively quiescent. The predicted acoustic resonant frequencies are in good agreement with those of the empirical formula. The mean flow streamlines are nearly horizontal along the mouth of the cavity. The pressure has its minimum value in the vortex core inside the cavity. The variation of the model coefficient predicted by the dynamic model is quite large between 0 and 0.3. The model coefficient increases in the stream-wise evolution of the shear layer and sharply decreases near the wall due to the wall effect.

Prediction of Small-Scale Cavitation in a High Speed Flow Over an Open Cavity Using Large-Eddy Simulation

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Ehsan Shams ◽  
Sourabh V. Apte
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Shear Layer ◽  
Transport Model ◽  
Open Cavity ◽  
Scalar Transport ◽  
Trailing Edge ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean

Large-eddy simulation of flow over an open cavity corresponding to the experimental setup of Liu and Katz (2008, “Cavitation Phenomena Occurring Due to Interaction of Shear Layer Vortices With the Trailing Corner of a Two-Dimensional Open Cavity,” Phys. Fluids, 20(4), p. 041702) is performed. The filtered, incompressible Navier–Stokes equations are solved using a co-located grid finite-volume solver with the dynamic Smagorinsky model for a subgrid-scale closure. The computational grid consists of around 7×106 grid points with 3×106 points clustered around the shear layer, and the boundary layer over the leading edge is resolved. The only input from the experimental data is the mean velocity profile at the inlet condition. The mean flow is superimposed with turbulent velocity fluctuations generated by solving a forced periodic duct flow at a freestream Reynolds number. The flow statistics, including mean and rms velocity fields and pressure coefficients, are compared with the experimental data to show reasonable agreement. The dynamic interactions between traveling vortices in the shear layer and the trailing edge affect the value and location of the pressure minima. Cavitation inception is investigated using two approaches: (i) a discrete bubble model wherein the bubble dynamics is computed by solving the Rayleigh–Plesset and the bubble motion equations using an adaptive time-stepping procedure and (ii) a scalar transport model for the liquid volume fraction with source and sink terms for phase change. Large-eddy simulation, together with the cavitation models, predicts that inception occurs near the trailing edge similar to that observed in the experiments. The bubble transport model captures the subgrid dynamics of the vapor better, whereas the scalar model captures the large-scale features more accurately. A hybrid approach combining the bubble model with the scalar transport is needed to capture the broad range of scales observed in cavitation.

On Homogenization-Based Methods for Large-Eddy Simulation

2002 ◽  
Vol 124 (4) ◽  
pp. 892-903 ◽  
Author(s):  
L. Persson ◽  
C. Fureby ◽  
N. Svanstedt
Keyword(s):  
Large Eddy Simulation ◽  
Large Scale ◽  
Stokes Equations ◽  
Multiple Scales ◽  
Practical Importance ◽  
Small Scale ◽  
Homogeneous Material ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy

The ability to predict complex engineering flows is limited by the available turbulence models and the present-day computer capacity. In Reynolds averaged numerical simulations (RANS), which is the most prevalent approach today, equations for the mean flow are solved in conjunction with a model for the statistical properties of the turbulence. Considering the limitations of RANS and the desire to study more complex flows, more sophisticated methods are called for. An approach that fulfills these requirements is large-eddy simulation (LES) which attempts to resolve the dynamics of the large-scale flow, while modeling only the effects of the small-scale fluctuations. The limitations of LES are, however, closely tied to the subgrid model, which invariably relies on the use of eddy-viscosity models. Turbulent flows of practical importance involve inherently three-dimensional unsteady features, often subjected to strong inhomogeneous effects and rapid deformation that cannot be captured by isotropic models. As an alternative to the filtering approach fundamental to LES, we here consider the homogenization method, which consists of finding a so-called homogenized problem, i.e. finding a homogeneous “material” whose overall response is close to that of the heterogeneous “material” when the size of the inhomogeneity is small. Here, we develop a homogenization-based LES-model using a multiple-scales expansion technique and taking advantage of the scaling properties of the Navier-Stokes equations. To study the model simulations of forced homogeneous isotropic turbulence and channel flow are carried out, and comparisons are made with LES, direct numerical simulation and experimental data.

Comparison of Four Eddy-Viscosity SGS Models in Large-Eddy Simulation of Flows Over Rough Walls

2004 ◽  
Author(s):  
Elie Bou-Zeid ◽  
Charles Meneveau ◽  
Marc B. Parlange
Keyword(s):  
Large Eddy Simulation ◽  
Dynamic Model ◽  
Eddy Viscosity ◽  
Complex Geometry ◽  
A Priori ◽  
Lagrangian Model ◽  
Scale Invariant ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Model Coefficient

Large Eddy Simulation (LES) has become an increasingly attractive option for turbulence modeling due to the rise in computing power and the improvement in sub-grid scale (SGS) parameterizations. This study tests the improvements in simulations of wall-bounded flows over heterogeneous surfaces attained by the implementation of three improvements in the eddy-viscosity SGS closure: the dynamic model by Germano et al. [1], the Lagrangian model by Meneveau et al. [2], and the scale-dependent approach by Porte´-Agel et al. [3]. The dynamic model consists of using the resolved scales to ‘measure’ the model coefficient during the simulation; therefore, no a-priori knowledge of the coefficient or the flow physics is needed. The traditional dynamic approach averages the coefficient over statistically homogeneous directions to numerically stabilize the simulations. The Lagrangian model relaxes the need for homogeneous directions by averaging the coefficient over pathlines, hence allowing local determination of the coefficient and facilitating applications to complex-geometry flows. The scale-dependent approach uses the dynamic formulation but does not assume that the SGS coefficients are scale-invariant, as is the case in traditional dynamic formulations. The deficiencies of the traditional Smagorinsky model are confirmed. Implementation of a dynamic model treats some of these deficiencies but is found to be under-dissipative close to the wall in high Reynolds number LES that does not resolve the viscous layer. The sensitivity of the model coefficient to the wall roughness is demonstrated thus confirming the need for a local SGS model such as the Lagrangian model used here. Finally, when the Lagrangian-dynamic model is implemented with the scale-dependent formulation, the results improve significantly.

RANS and Large Eddy Simulation of Internal Combustion Engine Flows—A Comparative Study

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Xiaofeng Yang ◽  
Saurabh Gupta ◽  
Tang-Wei Kuo ◽  
Venkatesh Gopalakrishnan
Keyword(s):  
Large Eddy Simulation ◽  
High Speed ◽  
Combustion Engine ◽  
Flow Analysis ◽  
Partial Geometry ◽  
Computational Domain ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Simulations

A comparative cold flow analysis between Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) cycle-averaged velocity and turbulence predictions is carried out for a single cylinder engine with a transparent combustion chamber (TCC) under motored conditions using high-speed particle image velocimetry (PIV) measurements as the reference data. Simulations are done using a commercial computationally fluid dynamics (CFD) code CONVERGE with the implementation of standard k-ε and RNG k-ε turbulent models for RANS and a one-equation eddy viscosity model for LES. The following aspects are analyzed in this study: The effects of computational domain geometry (with or without intake and exhaust plenums) on mean flow and turbulence predictions for both LES and RANS simulations. And comparison of LES versus RANS simulations in terms of their capability to predict mean flow and turbulence. Both RANS and LES full and partial geometry simulations are able to capture the overall mean flow trends qualitatively; but the intake jet structure, velocity magnitudes, turbulence magnitudes, and its distribution are more accurately predicted by LES full geometry simulations. The guideline therefore for CFD engineers is that RANS partial geometry simulations (computationally least expensive) with a RNG k-ε turbulent model and one cycle or more are good enough for capturing overall qualitative flow trends for the engineering applications. However, if one is interested in getting reasonably accurate estimates of velocity magnitudes, flow structures, turbulence magnitudes, and its distribution, they must resort to LES simulations. Furthermore, to get the most accurate turbulence distributions, one must consider running LES full geometry simulations.

Large Eddy Simulation of Cross Flow in Pipe Junction

2018 ◽  
Author(s):  
Jiajun Chen ◽  
Yue Sun ◽  
Hang Zhang ◽  
Dakui Feng ◽  
Zhiguo Zhang
Keyword(s):  
Large Eddy Simulation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Cross Flow ◽  
Exciting Force ◽  
Navier Stokes ◽  
Pipe Network ◽  
Eddy Simulation ◽  
Large Eddy

Mixing in pipe junctions can play an important role in exciting force and distribution of flow in pipe network. This paper investigated the cross pipe junction and proposed an improved plan, Y-shaped pipe junction. The numerical study of a three-dimensional pipe junction was performed for calculation and improved understanding of flow feature in pipe. The filtered Navier–Stokes equations were used to perform the large-eddy simulation of the unsteady incompressible flow in pipe. From the analysis of these results, it clearly appears that the vortex strength and velocity non-uniformity of centerline, can be reduced by Y-shaped junction. The Y-shaped junction not only has better flow characteristic, but also reduces head loss and exciting force. The results of the three-dimensional improvement analysis of junction can be used in the design of pipe network for industry.

scholarly journals Large-Eddy Simulation of Internal Flow through Human Vocal Folds

2018 ◽  
Vol 180 ◽  
pp. 02054
Author(s):  
Martin Lasota ◽  
Petr Šidlof
Keyword(s):  
Large Eddy Simulation ◽  
Stokes Equations ◽  
Turbulent Viscosity ◽  
Internal Flow ◽  
Vocal Folds ◽  
Computational Domain ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Scale Models ◽  
Large Eddy

The phonatory process occurs when air is expelled from the lungs through the glottis and the pressure drop causes flow-induced oscillations of the vocal folds. The flow fields created in phonation are highly unsteady and the coherent vortex structures are also generated. For accuracy it is essential to compute on humanlike computational domain and appropriate mathematical model. The work deals with numerical simulation of air flow within the space between plicae vocales and plicae vestibulares. In addition to the dynamic width of the rima glottidis, where the sound is generated, there are lateral ventriculus laryngis and sacculus laryngis included in the computational domain as well. The paper presents the results from OpenFOAM which are obtained with a large-eddy simulation using second-order finite volume discretization of incompressible Navier-Stokes equations. Large-eddy simulations with different subgrid scale models are executed on structured mesh. In these cases are used only the subgrid scale models which model turbulence via turbulent viscosity and Boussinesq approximation in subglottal and supraglottal area in larynx.

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