Reactive computational fluid dynamics modelling methane–hydrogen admixtures in internal combustion engines part II: Large eddy simulation

2020 ◽  
pp. 146808742091034
Author(s):  
Jann Koch ◽  
Christian Schürch ◽  
Yuri M Wright ◽  
Konstantinos Boulouchos
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Combustion Process ◽  
Flame Speed ◽  
Hydrogen Addition ◽  
Eddy Simulation ◽  
Modelling Framework ◽  
Large Eddy ◽  
Dynamics Modelling

Fuels based on admixtures of methane/natural gas and hydrogen are a promising way to reduce CO2 emissions of spark ignition engines and increase their efficiency. A lot of work was conducted experimentally, whereas only limited numerical work is available in the context of three-dimensional modelling of the full engine cycle. This work addresses this fact by proposing a reactive computational fluid dynamics modelling framework to consider the effects of hydrogen addition on the combustion process. Part I of this two-part study focuses on the modelling and crucial considerations in order to predict the mean cycle based on the G-equation combustion model using the Reynolds-averaged Navier–Stokes equations. There, the effect of increased burning speed was globally captured by increasing the flame speed coefficient A, appearing in the considered flame speed closure. The proposed simplified modelling of the early flame stage proved to be robust for the conducted hydrogen variation from 0 to 50 vol% H2 for stoichiometric and lean operation. Scope of this work, Part II, are cyclic fluctuations and the hydrogen influence thereon using large eddy simulation and the proposed modelling framework. The model is probed towards its capabilities to predict the fluctuation of the combustion process for 0 and 50 vol% H2 and correlations influencing the observed peak pressure of the individual cycle are presented. It is shown that the considered approach is capable to reproduce the cyclic fluctuations of the combustion process under the influence of hydrogen addition as well as lean operation. The importance of the early flame phase with respect to arising fluctuations is highlighted as well as the contribution of the resolved scales in terms of the flame front wrinkling.

Reactive computational fluid dynamics modelling of methane–hydrogen admixtures in internal combustion engines: Part I – RANS

2020 ◽  
pp. 146808742091638
Author(s):  
Jann Koch ◽  
Christian Schürch ◽  
Yuri M Wright ◽  
Konstantinos Boulouchos
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Internal Combustion Engines ◽  
Turbulent Flame ◽  
Internal Combustion ◽  
Flame Speed ◽  
Combustion Engines ◽  
Hydrogen Addition ◽  
Dynamics Modelling ◽  
Modelling Approach

The effects of hydrogen addition to internal combustion engines operated by natural gas/methane has been widely demonstrated experimentally in the literature. Already small hydrogen contents in the fuel show promising benefits with respect to increased engine efficiency, lower CO2 emissions, extended lean operating limits and a higher exhaust gas recirculation tolerance while maintaining the knock resistance of methane. In this article, the influence of hydrogen addition to methane on a spark ignited single cylinder engine is investigated. This article proposes a modelling approach to consider hydrogen addition within three-dimensional reactive computational fluid dynamics in order to establish a framework to gain further insights into the involved processes. Experiments have been performed on a single-cylinder spark-ignition engine situated at a test bed and cater as reference data for validating the proposed reactive computational fluid dynamics modelling approach based around the G-Equation combustion model. Within the course of the first part, crucial aspects relevant to the modelling of the mean engine cycle are highlighted. In this article, a simplified early combustion phase model which considers the transition towards a fully developed turbulent flame following ignition is introduced, along with a second submodel considering combined effects of the walls. The sensitivity of the combustion process towards the modelling approach is presented. The submodels were calibrated for a reference operating point, and a sweep in hydrogen content in the fuel as well as stoichiometric and lean operation has been considered. It is shown that the flame speed coefficient A appearing in the used turbulent flame speed closure, weighting the influence of the turbulent fluctuating speed [Formula: see text], has to be adjusted for different hydrogen contents. The introduced submodels allowed for significant improvement of the in-cylinder pressure and heat release rate evolution throughout all considered operating conditions.

Investigation of vehicle stability under crosswind conditions based on coupling methods

2019 ◽  
Vol 233 (13) ◽  
pp. 3305-3317 ◽  
Author(s):  
Taiming Huang ◽  
Shuya Li ◽  
Zhongmin Wan ◽  
Zhengqi Gu
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Coupling Method ◽  
Vehicle Stability ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Body Dynamics ◽  
Multi Body ◽  
Vehicle Movement

In this study, vehicle stability under crosswind conditions is investigated. A two-way coupling method is established based on computational fluid dynamics and vehicle multi-body dynamics. Large eddy simulation is employed in the computational fluid dynamics model to compute the transient aerodynamic load, and the accuracy of the large eddy simulation is validated with a wind tunnel experiment. The arbitrary Lagrange–Euler technique is used in the computational fluid dynamics simulation to realise vehicle motion, and a real-time data transmission method is employed to ensure effective exchange of data between the computational fluid dynamics and multi-body dynamics models. The robustness of the two-way coupling model is verified by changing the position of the vehicle centroid. The results of the two-way and one-way coupling simulations demonstrate that crosswinds significantly affect vehicle stability. There is a clear difference between the results obtained with the two methods, particularly after the disappearance of the crosswind. The main reason for the difference is that the interaction between the transient airflow and the vehicle movement is considered in the two-way coupling method. Therefore, investigations of vehicle stability under crosswind conditions should consider the coupling of transient aerodynamic force and vehicle movement.

Large eddy simulation of a homogeneously charged turbulent jet ignition system

2017 ◽  
Vol 20 (2) ◽  
pp. 181-193 ◽  
Author(s):  
Masumeh Gholamisheeri ◽  
Shawn Givler ◽  
Elisa Toulson
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Peak Pressure ◽  
Turbulent Jet ◽  
Navier Stokes ◽  
Rapid Compression Machine ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

Transient jet ignition of a homogeneous methane air mixture in a turbulent jet ignition system is studied computationally using a large eddy simulation turbulence model. The jet discharges from a prechamber into a main combustion chamber via one or more orifice(s) and provides a distributed ignition source in turbulent jet ignition. The effect of orifice size and stoichiometry is studied numerically using the Converge computational fluid dynamics code. A reduced kinetic mechanism is used for combustion along with a Smagorinsky sub-model for turbulence modeling. The computed pressure traces are compared with experimental measurements through rapid compression machine tests. Computational fluid dynamics results are in acceptable agreement with the experimental data during compression and the early stage of combustion; however, an over-prediction of peak pressure was reported. Peak pressure error is in the range of 0.1%–4% for Reynolds-averaged Navier–Stokes simulation estimation compared to the experimental measurements. This error is a function of mixture stoichiometry and unburned gas temperature. The error calculation showed that with the large eddy simulation model, 1% and 12% improvements in peak pressure and burn rate estimations, respectively, were achieved compared to Reynolds-averaged Navier–Stokes results. The reduced large eddy simulation error relative to the Reynolds-averaged Navier–Stokes simulations were considered to be in the acceptable range; however, further improvements could be achieved through validation and testing of additional turbulence models. In addition, computational fluid dynamics temperature contours for various nozzle orifices and air–fuel ratios are compared to achieve deeper insight into the turbulent jet ignition combustion process in the rapid compression machine combustion cylinder. The numerical iso-surface temperature contours were obtained which enabled three-dimensional views of the flame propagation, the jet discharge, ignition and extinction events. The heat release process and regeneration of mid-range temperature iso-surfaces (1200 K) were not visible through the experimental images.

scholarly journals An Overview of Hybrid RANS–LES Models Developed for Industrial CFD

2021 ◽  
Vol 11 (6) ◽  
pp. 2459
Author(s):  
Florian Menter ◽  
Andreas Hüppe ◽  
Alexey Matyushenko ◽  
Dmitry Kolmogorov
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Boundary Layers ◽  
Shear Flows ◽  
Low Cost ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd

An overview of scale-resolving simulation (SRS) methods used in ANSYS Computational Fluid Dynamics (CFD) software is provided. The main challenges, especially when computing boundary layers in large eddy simulation (LES) mode, will be discussed. The different strategies for handling wall-bound flows using combinations of RANS and LES models will be explained, along with some specific application examples. It will be demonstrated that the stress-blended eddy simulation (SBES) approach is optimal for applications with a mix of boundary layers and free shear flows due to its low cost and its ability to handle boundary layers in both RANS and wall-modeled LES (WMLES) modes.

Comparison of Unsteady Reynolds Averaged Navier–Stokes and Large Eddy Simulation Computational Fluid Dynamics Methodologies for Air Swirl Fuel Injectors

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
David Dunham ◽  
Adrian Spencer ◽  
James J. McGuirk ◽  
Mehriar Dianat
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Temporal Dynamics ◽  
Navier Stokes ◽  
Fuel Injector ◽  
Fuel Injectors ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

It is well documented that various large-scale quasiperiodic flow structures, such as a precessing vortex core (PVC) and multiple vortex helical instabilities, are present in the swirling flows typical of air swirl fuel injectors. Prediction of these phenomena requires time-resolved computational methods. The focus of the present work was to compare the performance and cost implications of two computational fluid dynamics (CFD) methodologies—unsteady Reynolds averaged Navier–Stokes (URANS) using a k-ε model and large eddy simulation (LES) for such flows. The test case was a single stream radial swirler geometry, which has been the subject of extensive experimental investigation. Both approaches captured the gross (time-mean) features of strongly swirling confined flows in reasonable agreement with experiment. The temporal dynamics of the quadruple vortex pattern emanating from within the swirler and observed experimentally were successfully predicted by LES, but not by URANS. Spectral analysis of two flow configurations (with and without a central jet) revealed various coherent frequencies embedded within the broadband turbulent frequency range. LES reproduced these characteristics, in excellent agreement with experimental data, whereas URANS predicted the presence of coherent motions but at incorrect amplitudes and frequencies. For the no-jet case, LES-predicted spectral data indicated the occurrence of a PVC, which was also observed experimentally for this flow condition; the URANS solution failed to reproduce this measured trend. On the evidence of this study, although k-ε based URANS offers considerable computational savings, its inability to capture the temporal characteristics of the flows studied here sufficiently accurately suggests that only LES-based CFD, which captures the stochastic nature of the turbulence much more faithfully, is to be recommended for fuel injector flows.

Large-eddy simulation of the flow in a direct injection spark ignition engine using an open-source framework

2020 ◽  
pp. 146808742090362
Author(s):  
Mateus Dias Ribeiro ◽  
Alex Mendonça Bimbato ◽  
Maurício Araújo Zanardi ◽  
José Antônio Perrella Balestieri ◽  
David P Schmidt
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Open Source ◽  
Direct Injection ◽  
Spark Ignition ◽  
Spark Ignition Engines ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Direct Injection Spark Ignition

Direct injection spark ignition engines aim at reducing specific fuel consumption and achieving the strict emission standards in state of the art internal combustion engines. This can be achieved by research comprising experimental methods, which are normally expensive and limited, and computational fluid dynamics methods, which are often more affordable and less restricted than their experimental counterpart. In the latter approach, the costs are mainly related to the acquisition, usage, and maintenance of computational resources, and the license cost when commercial computational fluid dynamics codes are used. Therefore, in order to make the research of direct injection spark ignition engines and their internal processes more accessible, this article proposes a novel open-source and free framework based on the OpenFOAM computational fluid dynamics library for the simulation of the internal flow in direct injection spark ignition engines using a large-eddy simulation closure for modeling the turbulence within the gas phase. Finally, this framework is tested by simulating the Darmstadt engine in motored operation, validating the results with experimental data compiled by the Darmstadt Engine Workshop.

Study on the Maximal Critical Velocity of Pressurization in Subway Station

2011 ◽  
Vol 250-253 ◽  
pp. 1781-1785
Author(s):  
Wei Zhong ◽  
Jian Peng Yang ◽  
Bao An Pei ◽  
Zi He Gao
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Prediction Model ◽  
Critical Velocity ◽  
3D Model ◽  
Subway Station ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Large Eddy

The prediction model of maximal critical velocity of pressurization was established theoretically by analyzed the pressure’s distribution in both sides of smoke bay. Using the computational fluid dynamics software FDS5.0 to build a 3D model of an island platform with platform edge door, Large Eddy Simulation model was used to obtain the critical velocity in different HRR, ceiling screen’s height and arrangement. Results show that the critical velocity rises with the increasing of HRR, and gradually reaching to the maximal critical velocity; in the range from 0 to 2m, it can be regarded that the maximal critical velocity is linear to ceiling screen’s height. The arrangement of ceiling screen has some influence on the critical velocity; setting ceiling screen around the staircase is more effective to restrict smoke.

scholarly journals MicroHH 1.0: a computational fluid dynamics code for direct numerical simulation and large-eddy simulation of atmospheric boundary layer flows

2017 ◽  
Vol 10 (8) ◽  
pp. 3145-3165 ◽  
Author(s):  
Chiel C. van Heerwaarden ◽  
Bart J. H. van Stratum ◽  
Thijs Heus ◽  
Jeremy A. Gibbs ◽  
Evgeni Fedorovich ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Numerical Simulation ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Processing Unit ◽  
Moist Convection ◽  
Eddy Simulation ◽  
Large Eddy

Abstract. This paper describes MicroHH 1.0, a new and open-source (www.microhh.org) computational fluid dynamics code for the simulation of turbulent flows in the atmosphere. It is primarily made for direct numerical simulation but also supports large-eddy simulation (LES). The paper covers the description of the governing equations, their numerical implementation, and the parameterizations included in the code. Furthermore, the paper presents the validation of the dynamical core in the form of convergence and conservation tests, and comparison of simulations of channel flows and slope flows against well-established test cases. The full numerical model, including the associated parameterizations for LES, has been tested for a set of cases under stable and unstable conditions, under the Boussinesq and anelastic approximations, and with dry and moist convection under stationary and time-varying boundary conditions. The paper presents performance tests showing good scaling from 256 to 32 768 processes. The graphical processing unit (GPU)-enabled version of the code can reach a speedup of more than an order of magnitude for simulations that fit in the memory of a single GPU.

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