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 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 Τυρβώδης ροή και διασπορά ρύπων στο αστικό περιβάλλον

2014 ◽  
Author(s):  
Νεκτάριος Κουτσουράκης
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Reynolds Averaged Navier Stokes

Στην παρούσα διατριβή έγινε ανάπτυξη υπολογιστικής μεθοδολογίας μοντελοποίησης μεγάλων δινών και χρήση της σε προβλήματα μελέτης της ροής του ανέμου και της διασποράς αέριων ρύπων ανάμεσα σε κτίρια. Η μοντελοποίηση μεγάλων δινών (Large Eddy Simulation – LES) είναι μια μεθοδολογία υπολογιστικής ρευστομηχανικής (Computational Fluid Dynamics – CFD) με την οποία είναι δυνατή η λεπτομερής χρονική επίλυση της ροής και η ανάλυση των μεγάλων δινών της τύρβης. Έτσι η LES ενδείκνυται ιδιαίτερα για μελέτη των ασταθών τυρβωδών ροϊκών φαινομένων που συμβαίνουν σε αστικές γεωμετρίες. Η μεθοδολογία LES που αναπτύχθηκε ενσωματώθηκε σε προϋπάρχοντα κώδικα CFD, τον ADREA-HF. Η αναπτυχθείσα LES χρησιμοποιεί μεταξύ των άλλων και μια πρωτότυπη μέθοδο δημιουργίας τεχνητής ψευδοτύρβης για χρήση σε οριακές συνθήκες του υπολογιστικού χωρίου, η οποία βασίζεται σε μια γενικευμένη εξίσωση τύπου Langevin. Για πιστοποίηση του κώδικα έγιναν μοντελοποιήσεις πλήρως ανεπτυγμένης ροής σε κανάλι, αλλά και ροής και διασποράς ρύπων σε οδικές χαράδρες. Επίσης εξετάστηκαν και πιο σύνθετες περιπτώσεις, όπως έκλυση και διασπορά υδρογόνου σε κλειστούς χώρους, ροή και διασπορά ρύπων σε ασύμμετρες οδικές χαράδρες, ροή πάνω από πολύ μεγάλη τραχύτητα εδάφους και τέλος ροή και διασπορά ρύπων σε μια πρωτότυπη γεωμετρία ημι-εξιδανικευμένης πόλης. Στις εφαρμογές που μελετήθηκαν έγινε επιτυχής σύγκριση με πειραματικά δεδομένα, οπότε η μεθοδολογία που αναπτύχθηκε αποδείχθηκε αξιόπιστη. Εκτός από την LES, χρησιμοποιήθηκε και η απλούστερη μεθοδολογία RANS (Reynolds-Averaged Navier-Stokes), προσδιορίστηκε ο σχετικός ρόλος των δύο μεθοδολογιών και αναδείχθηκαν οι δυνατότητες συμπληρωματικής χρήσης τους στο ίδιο πρόβλημα. Σε κάθε πρακτική εφαρμογή που εξετάστηκε, μελετήθηκαν κυρίως θέματα στα οποία υπήρχε κενό στη βιβλιογραφία. Μεταξύ άλλων προσδιορίστηκαν οι μηχανισμοί απαγωγής των ρύπων σε ασύμμετρες οδικές χαράδρες και υπολογίστηκε για πρώτη φορά ο κρίσιμος λόγος υψών για δημιουργία δύο στροβίλων σε χαράδρες μείωσης αναβαθμού. Επίσης μελετήθηκαν λεπτομερώς ασταθή ροϊκά φαινόμενα και τυρβώδεις δομές στην ημι-εξιδανικευμένη πόλη, αποκαλύπτοντας φαινόμενα όπως ριπές ανέμου, εξωθήσεις ρύπου, μη-γκαουσιανές κατανομές ταχυτήτων, αλλά και μηχανισμούς δημιουργίας κάποιων συνεκτικών δομών της τύρβης (ιδίως πεταλοειδών στροβίλων). Με τη μεθοδολογία LES, ανοίγονται νέοι ορίζοντες στη μελέτη της τυρβώδους ροής και της διασποράς ρύπων στο αστικό περιβάλλον.

Hybrid Large Eddy Simulation/Reynolds-Averaged Navier–Stokes Analysis of a Premixed Ethylene-Fueled Dual-Mode Scramjet Combustor

AIAA Journal ◽  
2021 ◽  
pp. 1-17
Author(s):  
Tanner B. Nielsen ◽  
Jack R. Edwards ◽  
Harsha K. Chelliah ◽  
Damien Lieber ◽  
Clayton Geipel ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Navier Stokes ◽  
Dual Mode ◽  
Eddy Simulation ◽  
Scramjet Combustor ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

scholarly journals Investigation of flow separation in a centrifugal pump impeller based on improved delayed detached eddy simulation method

2019 ◽  
Vol 11 (12) ◽  
pp. 168781401989783
Author(s):  
Yun Ren ◽  
Zuchao Zhu ◽  
Denghao Wu ◽  
Xiaojun Li ◽  
Lanfang Jiang
Keyword(s):  
Large Eddy Simulation ◽  
Centrifugal Pump ◽  
Flow Separation ◽  
Hybrid Algorithm ◽  
Internal Flow ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Vorticity Flux

The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.

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.

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.

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