The Effect of Stratification Ratio on the Macrostructure of Stratified Swirl Flames: Experimental and Numerical Study

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Xiao Han ◽  
Davide Laera ◽  
Aimee S. Morgans ◽  
Yuzhen Lin ◽  
Chih-Jen Sung
Keyword(s):  
Numerical Study ◽  
Large Eddy Simulations ◽  
Flame Dynamics ◽  
Large Eddy ◽  
Swirling Flame ◽  
Computational Fluid Dynamics Cfd ◽  
Different Shapes ◽  
Flame Quenching ◽  
Simulation Results ◽  
Good Agreement

The present paper reports experimental and numerical analyses of the macrostructures featured by a stratified swirling flame for varying stratification ratio (SR). The studies are performed with the Beihang Axial Swirler Independently Stratified (BASIS) burner, a novel double-swirled full-scale burner developed at Beihang University. Experimentally, it is found that depending on the ratio between the equivalence ratios of the methane–air mixtures from the two swirlers, the flame stabilizes with three different shapes: attached V-flame, attached stratified flame, and lifted flame. In order to better understand the mechanisms leading to the three macrostructures, large eddy simulations (LES) are performed via the open-source computational fluid dynamics (CFD) software OpenFOAM using the incompressible solver ReactingFoam. Changing SR, simulation results show good agreement with experimentally observed time-averaged flame shapes, demonstrating that the incompressible LES are able to fully characterize the different flame behaviors observed in stratified burners. When the LES account for heat loss from walls, they better capture the experimentally observed flame quenching in the outer shear layer (OSL). Finally, insights into the flame dynamics are provided by analyzing probes located near the two separate streams.

The Effect of Stratification Ratio on the Macrostructure of Stratified Swirl Flames: Experimental and Numerical Study

2018 ◽  
Author(s):  
Xiao Han ◽  
Davide Laera ◽  
Aimee S. Morgans ◽  
Yuzhen Lin ◽  
Chih-Jen Sung
Keyword(s):  
Fluid Dynamics ◽  
Numerical Study ◽  
Large Eddy Simulations ◽  
Flame Dynamics ◽  
Large Eddy ◽  
Swirling Flame ◽  
Different Shapes ◽  
Flame Quenching ◽  
Simulation Results ◽  
Good Agreement

The present article reports experimental and numerical analyses of the macrostructures featured by a stratified swirling flame for varying stratification ratio (SR). The studies are performed with the Beihang Axial Swirler Independently-Stratified (BASIS) burner, a novel double-swirled full-scale burner developed at Beihang University. Experimentally, it is found that depending on the ratio between the equivalence ratios of the methane-air mixtures from the two swirlers, the flame stabilizes with three different shapes: attached V–flame, attached stratified flame and lifted flame. In order to better understand the mechanisms leading to the three macrostructures, large eddy simulations (LES) simulations are performed via the open source Computational Fluid Dynamics software OpenFOAM using the incompressible solver Reacting Foam. Changing the SR, simulation results show good agreement with experimentally observed time-averaged flame shapes, demonstrating that the incompressible LES are able to fully characterize the different flame behaviours observed in stratified burners. When the LES account for heat loss from walls, they better capture the experimentally observed flame quenching in the outer shear layer. Finally, insights into the flame dynamics are provided by analysing probes located near the two separate streams.

scholarly journals Stability and Sensitivity Analysis of Hydrodynamic Instabilities in Industrial Swirled Injection Systems

2017 ◽  
Author(s):  
Thomas L. Kaiser ◽  
Thierry Poinsot ◽  
Kilian Oberleithner
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Vortex Core ◽  
Large Eddy Simulations ◽  
Mode Shapes ◽  
Mean Flow ◽  
Precessing Vortex Core ◽  
Large Eddy ◽  
Good Agreement

The hydrodynamic instability in an industrial, two-staged, counter-rotative, swirled injector of highly complex geometry is under investigation. Large eddy simulations show that the complicated and strongly nonparallel flow field in the injector is superimposed by a strong precessing vortex core. Mean flow fields of large eddy simulations, validated by experimental particle image velocimetry measurements are used as input for both local and global linear stability analysis. It is shown that the origin of the instability is located at the exit plane of the primary injector. Mode shapes of both global and local linear stability analysis are compared to a dynamic mode decomposition based on large eddy simulation snapshots, showing good agreement. The estimated frequencies for the instability are in good agreement with both the experiment and the simulation. Furthermore, the adjoint mode shapes retrieved by the global approach are used to find the best location for periodic forcing in order to control the precessing vortex core.

scholarly journals A Mixed-Fidelity Numerical Study for Fan–Distortion Interaction

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Yunfei Ma ◽  
Jiahuan Cui ◽  
Nagabhushana Rao Vadlamani ◽  
Paul Tucker
Keyword(s):  
Immersed Boundary Method ◽  
Numerical Study ◽  
Immersed Boundary ◽  
Fan Performance ◽  
Inlet Distortion ◽  
Eddy Simulation ◽  
Pressure Distributions ◽  
Large Eddy ◽  
Dynamics Method ◽  
Good Agreement

Inlet distortion often occurs under off-design conditions when a flow separates within an intake and this unsteady phenomenon can seriously impact fan performance. Fan–distortion interaction is a highly unsteady aerodynamic process into which high-fidelity simulations can provide detailed insights. However, due to limitations on the computational resource, the use of an eddy resolving method for a fully resolved fan calculation is currently infeasible within industry. To solve this problem, a mixed-fidelity computational fluid dynamics method is proposed. This method uses the large Eddy simulation (LES) approach to resolve the turbulence associated with separation and the immersed boundary method (IBM) with smeared geometry (IBMSG) to model the fan. The method is validated by providing comparisons against the experiment on the Darmstadt Rotor, which shows a good agreement in terms of total pressure distributions. A detailed investigation is then conducted for a subsonic rotor with an annular beam-generating inlet distortion. A number of studies are performed in order to investigate the fan's influence on the distortions. A comparison to the case without a fan shows that the fan has a significant effect in reducing distortions. Three fan locations are examined which reveal that the fan nearer to the inlet tends to have a higher pressure recovery. Three beams with different heights are also tested to generate various degrees of distortion. The results indicate that the fan can suppress the distortions and that the recovery effect is proportional to the degree of inlet distortion.

scholarly journals Experimental and Numerical Study on Dynamics of Two Footbridges with Different Shapes of Girders

2020 ◽  
Vol 10 (13) ◽  
pp. 4505 ◽  
Author(s):  
Anna Banas ◽  
Robert Jankowski
Keyword(s):  
Natural Vibration ◽  
Numerical Study ◽  
Numerical Results ◽  
Vibration Exciter ◽  
Structural Vibrations ◽  
Impulse Load ◽  
Different Shapes ◽  
Comfort Criteria ◽  
Good Agreement

The paper presents the experimental and numerical results of the dynamic system identification and verification of the behavior of two footbridges in Poland. The experimental part of the study involved vibration testing under different scenarios of human-induced load, impulse load, and excitations induced by vibration exciter. Based on the results obtained, the identification of dynamic parameters of the footbridges was performed using the peak-picking method. With the impulse load applied to both structures, determination of their natural vibration frequencies was possible. Then, based on the design drawings, detailed finite element method (FEM) models were developed, and the numerical analyses were carried out. The comparison between experimental and numerical results obtained from the modal analysis showed a good agreement. The results also indicated that both structures under investigation have the first natural bending frequency of the deck in the range of human-induced excitation. Therefore, the risk of excessive structural vibrations caused by pedestrian loading was then analysed for both structures. The vibration comfort criteria for both footbridges were checked according to Sétra guidelines. In the case of the first footbridge, the results showed that the comfort criteria are fulfilled, regardless of the type of load. For the second footbridge, it was emphasized that the structure meets the assumptions of the guidelines for vibration severability in normal use; nevertheless, it is susceptible to excitations induced by synchronized users, even in the case of a small group of pedestrians.

Heat Transfer Evaluation for a Two-Pass Smooth Wall Channel: Stationary and Rotating Cases

2019 ◽  
Vol 142 (6) ◽  
Author(s):  
Mandana S. Saravani ◽  
Nicholas J. DiPasquale ◽  
Ahmad I. Abbas ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotational Speed ◽  
Numerical Study ◽  
Flow Behavior ◽  
Smooth Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

Abstract This study presents findings on combined effects of Reynolds number and rotational effect for a two-pass channel with a 180-deg turn, numerically and experimentally. To have a better understanding of the flow behavior and to create a baseline for future studies, a smooth wall channel with the square cross section is used in this study. The Reynolds number varies between 6000 and 35,000. Furthermore, by changing the rotational speed, the maximum rotation number of 1.5 is achieved. For the numerical investigation, large eddy simulation (LES) is utilized. Results from the numerical study show a good agreement with the experimental data. From the results, it can be concluded that increasing both Reynolds number and rotational speed is in favor of the heat transfer coefficient enhancement, especially in the turn region.

scholarly journals Understanding the diesel-like spray characteristics applying a flamelet-based combustion model and detailed large eddy simulations

2019 ◽  
Vol 21 (1) ◽  
pp. 134-150 ◽  
Author(s):  
Eduardo J Pérez-Sánchez ◽  
Jose M Garcia-Oliver ◽  
Ricardo Novella ◽  
Jose M Pastor
Keyword(s):  
Flame Stabilization ◽  
Large Eddy Simulations ◽  
Combustion Model ◽  
Progress Variable ◽  
Auto Ignition ◽  
Large Eddy ◽  
Engine Combustion ◽  
Spatial Fields ◽  
Lift Off ◽  
Good Agreement

This investigation analyses the structure of spray A from engine combustion network (ECN), which is representative of diesel-like sprays, by means of large eddy simulations and an unsteady flamelet progress variable combustion model. A very good agreement between modelled and experimental measurements is obtained for the inert spray that supports further analysis. A parametric variation in oxygen concentration is carried out in order to describe the structure of the flame and how it is modified when mixture reactivity is changed. The most relevant trends for the flame metrics, ignition delay and lift-off length are well-captured by the simulations corroborating the suitability of the model for this type of configuration. Results show that the morphology of the flame is strongly affected by the boundary conditions in terms of the reactive scalar spatial fields and Z–T maps. The filtered instantaneous fields provided by the simulations allow investigation of the structure of the flame at the lift-off length, whose positioning shows low fluctuations, and how it is affected by turbulence. It is evidenced that small ignition kernels appear upstream and detached from the flame that eventually merge with its base in agreement with experimental observations, leading to state that auto-ignition plays a key role as one of the flame stabilization mechanisms of the flame.

scholarly journals ICCM2015: A Comparison of RANS and LES Computational Methods in Analyzing Ventilation Flow Through a Room Fitted with a Two-Sided Windcatcher

2017 ◽  
Vol 14 (03) ◽  
pp. 1750021 ◽  
Author(s):  
A. Niktash ◽  
B. P. Huynh
Keyword(s):  
Natural Ventilation ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Interior Space ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Cfd Method ◽  
Good Agreement

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

Analysis and modelling of subgrid-scale motions in near-wall turbulence

1998 ◽  
Vol 356 ◽  
pp. 327-352 ◽  
Author(s):  
CARLOS HÄRTEL ◽  
LEONHARD KLEISER
Keyword(s):  
Eddy Viscosity ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Large Eddy Simulations ◽  
Inverse Cascade ◽  
Large Eddy ◽  
Wall Flow ◽  
Definition Of ◽  
Subgrid Stress ◽  
Near Wall

A numerical study of turbulent channel flow at various Reynolds numbers (Reτ=115, 210, 300) is conducted in order to examine the requirements for a reliable subgrid modelling in large-eddy simulations of wall-bounded flows. Using direct numerical simulation data, the interactions between large and small scales in the near-wall flow are analysed in detail which sheds light on the origin of the inverse cascade of turbulent kinetic energy observed in the buffer layer. It is shown that the correlation of the wall-normal subgrid stress and the wall-normal derivative of the streamwise grid-scale velocity plays the key role in the occurrence of the inverse cascade. A brief a priori test of several subgrid models shows that currently applied models are not capable of accounting properly for the complex interactions in the near-wall flow. A series of large-eddy simulations gives evidence that this deficiency may cause significant errors in important global quantities of the flow such as the mean wall shear stress. A study of the eddy-viscosity ansatz is conducted which reveals that the characteristic scales usually employed for the definition of the eddy viscosity are inappropriate in the vicinity of a wall. Therefore, a novel definition of the eddy viscosity is derived from the analysis of the near-wall energy budget. This new definition, which employs the wall-normal subgrid stress as a characteristic scale, is more consistent with the near-wall physics. No significant Reynolds-number effects are encountered in the present analysis which suggests that the findings may be generalized to flows at higher Reynolds numbers.

Comparison of Partially Averaged Navier–Stokes and Large-Eddy Simulations of the Flow Around a Cuboid Influenced by Crosswind

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Siniša Krajnović ◽  
Per Ringqvist ◽  
Branislav Basara
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Better Than ◽  
Good Agreement ◽  
Near Wall

The paper presents a partially averaged Navier–Stokes (PANS) simulation of the flow around a cuboid influenced by crosswind. The results of the PANS prediction are validated against experimental data and results of a large-eddy simulation (LES) made using the same numerical conditions as PANS. The PANS shows good agreement with the experimental data. The prediction of PANS was found to be better than that of the LES in flow regions where simulations suffered from poor near-wall resolution.

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