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.

RANS and LES of IC Engine Flows: A Comparative Study

2013 ◽  
Author(s):  
Xiaofeng Yang ◽  
Saurabh Gupta ◽  
Tang-Wei Kuo ◽  
Venkatesh Gopalakrishnan
Keyword(s):  
High Speed ◽  
Flow Analysis ◽  
Navier Stokes ◽  
Partial Geometry ◽  
Computational Domain ◽  
Mean Flow ◽  
Ic Engine ◽  
Eddy Simulation ◽  
Eddy Viscosity Model ◽  
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 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 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: 1. 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 2. 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 full geometry simulations. The guideline therefore for CFD engineers is that RANS partial geometry simulations (computationally least expensive) are good enough for capturing overall qualitative flow trends. 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 for a Deep Surge Cycle in a High-Speed Centrifugal Compressor With Vaned Diffuser

2015 ◽  
Vol 137 (10) ◽  
Author(s):  
Ibrahim Shahin ◽  
Mohamed Gadala ◽  
Mohamed Alqaradawi ◽  
Osama Badr
Keyword(s):  
High Pressure ◽  
Large Eddy Simulation ◽  
Centrifugal Compressor ◽  
Pressure Fluctuation ◽  
High Speed ◽  
Computational Study ◽  
Mean Flow ◽  
Vaned Diffuser ◽  
Eddy Simulation ◽  
Large Eddy

This paper presents a computational study for a high-speed centrifugal compressor stage with a design pressure ratio equal to 4, the stage consisting of a splittered unshrouded impeller and a wedged vaned diffuser. The aim of this paper is to investigate numerically the modifications of the flow structure during a surge cycle. The investigations are based on the results of unsteady three-dimensional, compressible flow simulations, using large eddy simulation (LES) model. Instantaneous and mean flow field analyses are presented in the impeller inducer and in the vaned diffuser region through one surge cycle time intervals. The computational data compare favorably with the measured data, from the literature, for the same compressor and operational point. The surge event phases are well detected inside the impeller and diffuser. The time-averaged loading on the impeller main blade is maximum near the trialing edge and near the tip. The amplitude of the unsteady pressure fluctuation is maximum for the flow reversal condition and reaches values up to 70% of the dynamic pressure. The diffuser vane exhibits high-pressure fluctuation from the vane leading edge to 50% of the chord length. High-pressure fluctuation is detected during the forward flow recovery condition as a result of the shock wave that moves toward the diffuser outlet.

Large-Eddy Simulation of Spatially Developing Turbulent Wake Flows

2006 ◽  
Vol 50 (03) ◽  
pp. 208-221
Author(s):  
Shaoping Shi ◽  
Ismail Celik ◽  
Andrei Smirnov ◽  
Ibrahim Yavuz
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Shear Stresses ◽  
Computational Domain ◽  
Mean Flow ◽  
Ship Wake ◽  
Wake Flows ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Wakes

The feasibility of applying the large-eddy simulation (LES) technique in complex high Reynolds number flows has been studied. The focus of the study is on the spatially developing wake flows with an application to ship wakes. The bluff body that generates the wake is excluded from the computational domain. To make this possible, a new random flow generation technique (RFG) is used to provide the turbulent inflow boundary conditions as a function of time. The technique provides an instantaneous velocity field at the inlet boundary in conjunction with the prescribed mean flow field obtained either from RANS (Reynolds averaged Navier-Stokes) simulations or from experimental data. The combined LES-RFG procedure has been validated in previous publications in cases of a flat plate and a mixing layer. At the inflow boundary, turbulence characteristics, including the shear stresses, were reconstructed. The time averaged results showed good agreement with the experiments in the developing wake. The same procedure is used to simulate a ship wake (ship model DTMB 5512) in the near field of 1.5 ship cord length. The LES technique captured both spatial and temporal development of the large coherent structures that play an important role in the evaluation of bubble concentration in the ship wakes. These structures are usually smeared out in RANS simulations.

Large Eddy Simulation of a Hot, High Speed Coflowing Jet

2011 ◽  
Author(s):  
Simon Eastwood ◽  
Paul G. Tucker ◽  
Hao Xia
Keyword(s):  
Large Eddy Simulation ◽  
High Speed ◽  
Eikonal Equation ◽  
Navier Stokes ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ray Trajectories ◽  
Inlet Conditions ◽  
Bypass Ratio

Computations are made of a short cowl coflowing jet nozzle with a bypass ratio 8 : 1. The core flow is heated, making the inlet conditions reminiscent of those for a real engine. A large eddy resolving approach is used with a 12 × 106 cell mesh. Since the code being used tends towards being dissipative the sub-grid scale (SGS) model is abandoned giving what can be termed Numerical Large Eddy Simulation (NLES). To overcome near wall modelling problems a hybrid NLES-RANS (Reynolds Averaged Navier-Stokes) related method is used. For y+ ≤ 60 a k–l model is used. Blending between the two regions makes use of the differential Hamilton-Jabobi (HJ) equation, an extension of the eikonal equation. Results show encouraging agreement with existing measurements of other workers. The eikonal equation is also used for acoustic ray tracing to explore the effect of the mean flow on acoustic ray trajectories, thus yielding a coherent solution strategy.

scholarly journals Flow Asymmetry in Symmetric Multiple Impinging Jets: A Large Eddy Simulation Approach

2011 ◽  
Vol 8 (2) ◽  
pp. 40 ◽  
Author(s):  
N. Kharoua ◽  
L. Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Numerical Study ◽  
Impinging Jets ◽  
Heated Plate ◽  
Computational Domain ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features ◽  
The Asymmetry

 A numerical study on in-line arrays of multiple turbulent round impinging jets on a flat heated plate was conducted. The Large Eddy Simulation turbulence model was used to capture details of the instantaneous and mean flow fields. The Reynolds number, based on the jets diameter, was equal to 20,000. In addition to flow features known from single jets, the interaction between the neighboring jets was successfully elucidated. Symmetry boundary conditions were imposed to reduce the computational domain to only a quarter. In accordance with previous numerical and experimental works, the asymmetry in the velocity field near to the impingement plate was also found to exist. LES showed oval imprints of the Nusselt number similar to experiments but with some discrepancies on the symmetry boundaries. The asymmetry, observed in previous experimental and numerical results, in the horizontal planes, parallel and close to the impingement wall, was confirmed. The recirculation zone responsible for asymmetry, known to develop due to the wall jets interaction, was seen in only one side of the diagonal formed by the central and the farthest jets. 

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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