Multidimensional Predictions of In-Cylinder Turbulent Flows: Contribution to the Assessment of k-ε Turbulence Model Variants for Bowl-in-Piston Engines

2003 ◽  
Author(s):  
Andrea E. Catania ◽  
Mirko Baratta ◽  
Ezio Spessa ◽  
Rui L. Liu
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Fluid Motion ◽  
Combustion Process ◽  
Turbulence Models ◽  
Algebraic Equations ◽  
Mean Flow ◽  
Wall Functions ◽  
Simpler Algorithm ◽  
Model Engine

As is well known, the in-cylinder flow phenomena can strongly affect the engine combustion process and the related emission sources. Therefore, a better understanding of the fluid motion is critical for developing new engine concepts with the most attractive operation and emission characteristics. To that end, multidimensional flow computational codes with reliable turbulence models are useful investigation and design tools. This paper is concerned with mean-flow and turbulence simulation in a motored model engine with a compression ratio of 6.7. The flow configurations comprise an axisymmetric combustion chamber with one centrally located valve and each of a flat piston and cylindrical bowl-in-piston arrangements. The calculations are performed using a non-commercial CFD code that was originally developed by the authors. A finite volume conservative implicit method, applying various order-of-accuracy schemes, is employed for the discretization of the partial differential equations modeling the in-cylinder turbulent flow, and the resultant algebraic equations are linearized and sequentially solved by an iterative procedure. Velocity-pressure coupling is ensured by a pressure correction method similar to that of the SIMPLER algorithm. Results of the simulation are presented at the model engine speed of 200 rpm throughout the engine cycle. They were obtained using three versions of the k-ε turbulence model (Standard, Two Scale and RNG) which differ from each other for underlying concepts, complexity and accuracy in capturing flow features. Modified boundary conditions with respect to logarithmic wall-functions were applied. Insight was also gained into the nonlinear effects of stress-strain constitutive relation on turbulence modeling. The effects of the equation differencing schemes and computational grid spacing on flow predictions were tested. Then the numerical results were compared to those of LDV measurements and the influence of the k-ε model variants on the flow field features were examined during the induction stroke and around compression TDC.

Multidimensional Predictions of In-Cylinder Turbulent Flows: Contribution to the Assessment of k-ε Turbulence Model Variants for Bowl-in-Piston Engines

2005 ◽  
Vol 127 (4) ◽  
pp. 883-896 ◽  
Author(s):  
Mirko Baratta ◽  
Andrea E. Catania ◽  
Ezio Spessa ◽  
Rui L. Liu
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Internal Combustion Engines ◽  
Flow Analysis ◽  
Combustion Process ◽  
Turbulence Models ◽  
Wall Functions ◽  
Spacing Effects ◽  
Flow Phenomena ◽  
Cylinder Flow

Multidimensional computational fluid dynamics (CFD) codes with reliable turbulence models are useful investigation and design tools for internal combustion engines, in-cylinder flow phenomena being critical to the combustion process and related emission sources. Although a variety of turbulence models has long been proposed, the assessment of even the most widely used k-ε model is still lacking, especially for bowl-in-piston engines. This paper provides a survey of k-ε turbulence model variants and their numerical implementation for in-cylinder flow analysis. Mean motion and turbulence quantities were simulated in the axisymmetric combustion chamber of a motored model engine featuring one centrally located valve and each of a flat-piston and cylindrical bowl-in-piston arrangements. A noncommercial CFD code developed by the authors was applied for calculation, using a finite-volume conservative implicit method and applying various order-of-accuracy numerical schemes. Simulation results are presented at the engine speed of 200 rpm throughout the whole engine cycle. These were obtained using three k-ε turbulence model versions, standard, renormalization group (RNG) and two scale, each of which focuses on one main engine flow feature, i.e., compressibility, anisotropy, and high unsteadiness, respectively. Modified boundary conditions with respect to conventional logarithmic wall functions were applied. Effects of equation-differencing scheme and computational-grid spacing effects on flow predictions were tested. The numerical results were compared to those of laser Doppler velocimetry measurements and the influence of the k-ε model variants on the flow-field features was examined during the induction stroke and around compression top dead center. For the flat-piston case, a comparison between the homemade and commercial STAR-CD® code results was also made.

A Turbulence Model for Pulsatile Arterial Flows

2004 ◽  
Vol 126 (5) ◽  
pp. 578-584 ◽  
Author(s):  
B. A. Younis ◽  
S. A. Berger
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Solid Wall ◽  
Flow Behavior ◽  
Local Equilibrium ◽  
Fluid Motion ◽  
Circulatory System ◽  
Wave Form ◽  
Mean Flow ◽  
Law Of The Wall

Difficulties in predicting the behavior of some high Reynolds number flows in the circulatory system stem in part from the severe requirements placed on the turbulence model chosen to close the time-averaged equations of fluid motion. In particular, the successful turbulence model is required to (a) correctly capture the “nonequilibrium” effects wrought by the interactions of the organized mean-flow unsteadiness with the random turbulence, (b) correctly reproduce the effects of the laminar-turbulent transitional behavior that occurs at various phases of the cardiac cycle, and (c) yield good predictions of the near-wall flow behavior in conditions where the universal logarithmic law of the wall is known to be not valid. These requirements are not immediately met by standard models of turbulence that have been developed largely with reference to data from steady, fully turbulent flows in approximate local equilibrium. The purpose of this paper is to report on the development of a turbulence model suited for use in arterial flows. The model is of the two-equation eddy-viscosity variety with dependent variables that are zero-valued at a solid wall and vary linearly with distance from it. The effects of transition are introduced by coupling this model to the local value of the intermittency and obtaining the latter from the solution of a modeled transport equation. Comparisons with measurements obtained in oscillatory transitional flows in circular tubes show that the model produces substantial improvements over existing closures. Further pulsatile-flow predictions, driven by a mean-flow wave form obtained in a diseased human carotid artery, indicate that the intermittency-modified model yields much reduced levels of wall shear stress compared to the original, unmodified model. This result, which is attributed to the rapid growth in the thickness of the viscous sublayer arising from the severe acceleration of systole, argues in favor of the use of the model for the prediction of arterial flows.

Computations of Flow Field and Heat Transfer in a Stator Vane Passage Using the v2¯−f Turbulence Model

2005 ◽  
Vol 127 (3) ◽  
pp. 627-634 ◽  
Author(s):  
A. Sveningsson ◽  
L. Davidson
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Mean Flow ◽  
Stator Vane ◽  
Good Agreement

In this study three-dimensional simulations of a stator vane passage flow have been performed using the v2¯−f turbulence model. Both an in-house code (CALC-BFC) and the commercial software FLUENT are used. The main objective is to investigate the v2¯−f model’s ability to predict the secondary fluid motion in the passage and its influence on the heat transfer to the end walls between two stator vanes. Results of two versions of the v2¯−f model are presented and compared to detailed mean flow field, turbulence, and heat transfer measurements. The performance of the v2¯−f model is also compared with other eddy-viscosity-based turbulence models, including a version of the v2¯−f model, available in FLUENT. The importance of preventing unphysical growth of turbulence kinetic energy in stator vane flows, here by use of the realizability constraint, is illustrated. It is also shown that the v2¯−f model predictions of the vane passage flow agree well with experiments and that, among the eddy-viscosity closures investigated, the v2¯−f model, in general, performs the best. Good agreement between the two different implementations of the v2¯−f model (CALC-BFC and FLUENT) was obtained.

Computations of Flow Field and Heat Transfer in a Stator Vane Passage Using the v2–f Turbulence Model

2004 ◽  
Author(s):  
Andreas Sveningsson ◽  
Lars Davidson
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Mean Flow ◽  
Stator Vane ◽  
Good Agreement

In this study three-dimensional simulations of a stator vane passage flow have been performed using the v2–f turbulence model. Both an in-house code (CALC-BFC) and the commercial software Fluent are used. The main objective is to investigate the v2–f model’s ability to predict the secondary fluid motion in the passage and its influence on the heat transfer to the endwalls between two stator vanes. Results of two versions of the v2–f model are presented and compared with detailed mean flow field, turbulence and heat transfer measurements. The performance of the v2–f model is also compared with other eddy-viscosity based turbulence models, including a version of the v2–f model, available in Fluent. The importance of preventing unphysical growth of turbulence kinetic energy in stator vane flows, here by use of the realizability constraint, is illustrated. It is also shown that the v2–f model predictions of the vane passage flow agree well with experiments and that, amongst the eddy-viscosity closures investigated, the v2–f model in general performs the best. Good agreement between the two different implementations of the v2–f model (CALC-BFC and Fluent) was obtained.

Improved Prediction of Turbomachinery Flows Using Near-Wall Reynolds-Stress Model

2001 ◽  
Vol 124 (1) ◽  
pp. 86-99 ◽  
Author(s):  
G. A. Gerolymos ◽  
J. Neubauer ◽  
V. C. Sharma ◽  
I. Vallet
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Flow Equations ◽  
Near Wall

In this paper an assessment of the improvement in the prediction of complex turbomachinery flows using a new near-wall Reynolds-stress model is attempted. The turbulence closure used is a near-wall low-turbulence-Reynolds-number Reynolds-stress model, that is independent of the distance-from-the-wall and of the normal-to-the-wall direction. The model takes into account the Coriolis redistribution effect on the Reynolds-stresses. The five mean flow equations and the seven turbulence model equations are solved using an implicit coupled OΔx3 upwind-biased solver. Results are compared with experimental data for three turbomachinery configurations: the NTUA high subsonic annular cascade, the NASA_37 rotor, and the RWTH 1 1/2 stage turbine. A detailed analysis of the flowfield is given. It is seen that the new model that takes into account the Reynolds-stress anisotropy substantially improves the agreement with experimental data, particularily for flows with large separation, while being only 30 percent more expensive than the k−ε model (thanks to an efficient implicit implementation). It is believed that further work on advanced turbulence models will substantially enhance the predictive capability of complex turbulent flows in turbomachinery.

Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart–Shur Correction Term

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Pavel E. Smirnov ◽  
Florian R. Menter
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Transport Model ◽  
Correction Term ◽  
Computational Cost ◽  
Turbulence Models ◽  
Reynolds Stress Transport Model ◽  
Wide Range ◽  
Sst Model ◽  
The One

A rotation-curvature correction suggested earlier by Spalart and Shur (1997, “On the Sensitization of Turbulence Models to Rotation and Curvature,” Aerosp. Sci. Technol., 1(5), pp. 297–302) for the one-equation Spalart–Allmaras turbulence model is adapted to the shear stress transport model. This new version of the model (SST-CC) has been extensively tested on a wide range of both wall-bounded and free shear turbulent flows with system rotation and/or streamline curvature. Predictions of the SST-CC model are compared with available experimental and direct numerical simulations (DNS) data, on the one hand, and with the corresponding results of the original SST model and advanced Reynolds stress transport model (RSM), on the other hand. It is found that in terms of accuracy the proposed model significantly improves the original SST model and is quite competitive with the RSM, whereas its computational cost is significantly less than that of the RSM.

Differential stress modelling of turbulent flows in model reciprocating engines

1997 ◽  
Vol 211 (1) ◽  
pp. 59-77 ◽  
Author(s):  
C. J. Lea ◽  
A. P. Watkins
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Turbulence Intensity ◽  
Laser Doppler Anemometry ◽  
Turbulence Models ◽  
Apparent Difference ◽  
Mean Flow ◽  
Differential Stress ◽  
Reciprocating Engines ◽  
The Mean

A study is made here of the application of a differential stress model (DSM) of turbulence to flows in two model reciprocating engines. For the first time this study includes compressive effects. An assessment between DSM and k-ɛ results is made comparing with laser Doppler anemometry experimental data of the mean flow and turbulence intensity levels during intake and compression strokes. A well-established two-dimensional finite-volume computer code is employed. Two discretization schemes are used, namely the HYBRID scheme and the QUICK scheme. The latter is found to be essential if differentiation is to be made between the turbulence models. During the intake stroke the DSM results are, in general, similar to the k-ɛ results in comparison to the experimental data, except for the turbulence levels, which the DSM seriously underpredicts. This is in contrast to a parallel set of calculations of steady in-flow, which showed significant gains from using the DSM, particularly at the turbulence field level. The increased number of grid lines employed in those calculations contribute to this apparent difference between steady and unsteady flows, but cycle- to-cycle variations are more likely to be the primary cause, resulting in too high levels of turbulence intensity being measured. However, during the compression stroke the DSM returns vastly superior results to the k-ɛ model at both the mean flow and turbulence intensity levels. This is because the DSM generates an anisotropic shear stress field during the early stages of compression that suppresses the main vortical structure, in line with the experimental data.

scholarly journals Characterization of Model-Based Uncertainties in Incompressible Turbulent Flows by Machine Learning

2018 ◽  
Author(s):  
Mustafa Usta ◽  
Ali Tosyali
Keyword(s):  
Machine Learning ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Machine Learning Algorithms ◽  
Mean Flow ◽  
Flow Properties ◽  
Significant Discrepancy ◽  
Model Based ◽  
Flow Features

This work determines the inaccuracy of using Reynolds averaged Navier Stokes (RANS) turbulence models in transition to turbulent flow regimes by predicting the model-based discrepancies between RANS and large eddy simulation (LES) models. Then, it incorporates the capabilities of machine learning algorithms to characterize the discrepancies which are defined as a function of mean flow properties of RANS simulations. First, three-dimensional CFD simulations using k-omega Shear Stress Transport (SST) and dynamic one-equation subgrid-scale models are conducted in a wall-bounded channel containing a cylinder for RANS and LES, respectively, to identify the turbulent kinetic energy discrepancy. Second, several flow features such as viscosity ratio, wall-distance based Reynolds number, and vortex stretching are calculated from the mean flow properties of RANS. Then the discrepancy is regressed on these flow features using the Random Forests regression algorithm. Finally, the discrepancy of the test flow is predicted using the trained algorithm. The results reveal that a significant discrepancy exists between RANS and LES simulations, and ML algorithm successfully predicts the increased model uncertainties caused by the employment of k-omega SST turbulence model for transitional fluid flows.

CFD Simulation of Single-Phase and Dilute Particulate Turbulent Flows in 90° Duct Bends

2003 ◽  
Author(s):  
Benny T. Kuan ◽  
M. Philip Schwarz
Keyword(s):  
Turbulent Flows ◽  
Single Phase ◽  
Cfd Simulation ◽  
Experimental Testing ◽  
Fluid Motion ◽  
Circular Cross Section ◽  
Turbulence Models ◽  
Continuous Phase ◽  
Two Phase ◽  
Duct Bends

Single-phase and two-phase (gas-solid) turbulent flow calculations are performed for 90° duct bends having radii of curvature ranging from 1.5 to 2.0 duct diameter, and with either a square or circular cross-section. The considered flow Reynolds number is between 6×104 and 3×105, and the particulate flows examined pertain to two different solid mass loading ratios: 1.5×10−4 and 0.33. Numerous turbulence models have been utilized to simulate the turbulent fluid motion within the duct bend while particle trajectories are calculated on the basis of a Lagrangian approach. Reasonable agreement with the experimental data is achieved for the continuous phase in the cases tested. In contrast, significant disparities with the measurements arise in particle tracking calculations, especially in regions where particle rope dispersion is predominant. Results of this investigation indicate the need for more experimental testing of mill-duct flows of similar configuration in order to facilitate a better understanding and modeling of strongly curved gas-solid duct flows.

On Turbulent Flows Dominated by Curvature Effects

1992 ◽  
Vol 114 (1) ◽  
pp. 52-57 ◽  
Author(s):  
G. C. Cheng ◽  
S. Farokhi
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Dominant Role ◽  
Longitudinal Velocity ◽  
Turbulence Models ◽  
Separated Flows ◽  
Local Curvature ◽  
Streamline Curvature ◽  
Curvature Effects ◽  
Numerical Predictions

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows and the flow in a curved duct are examples of flow fields where streamline curvature plays a dominant role. New algebraic formulations for the eddy viscosity μt incorporating the k–ε turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal (where axial velocities change signs) of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the longitudinal velocity and the static pressure in an S-bend duct and in 180 deg turn-around ducts. The numerical predictions of different curvature effects by the proposed turbulence models are also reported.

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