scholarly journals Numerical Simulation of Interaction between Large-Scale Congestion and Vent during the Natural Gas Explosion in a Kitchen

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Lei Pang ◽  
Mengjie Jin ◽  
Qianran Hu ◽  
Kai Yang
Keyword(s):  
Natural Gas ◽  
Flow Field ◽  
Flame Propagation ◽  
Combustion Rate ◽  
Large Scale ◽  
Small Scale ◽  
Propagation Mode ◽  
Gas Explosion ◽  
Flame Propagation Velocity ◽  
Explosion Process

The influence of large-scale congestion on a confined natural gas explosion in a typical Chinese kitchen was studied using the computational fluid dynamics technology. It was found that opening the explosion venting surface promotes the development of turbulence, flame propagation velocity, and multipeak overpressure in the explosion flow field. Large-scale congestion can significantly strengthen the influence of the explosion venting surface on the flow field; the congestion and the explosion venting surface have a synergistic effect on the explosion flow field. At the moment of gas explosion, the flow fields in each area of the kitchen exhibit different distribution characteristics. A flow field near small-scale congestion is more likely to produce greater turbulence, combustion rate, and flame speed. The obstruction effect of large-scale congestion perpendicular to the flame propagation direction is dominant. The indoor flame propagation speed and overpressure development speed increase and the peak combustion rate and indoor peak overpressure decrease with an increase in obstacle blockage. Increases in the large-scale volume congestion rate and volume blockage in the kitchen induce changes in the indoor flame propagation mode and increase the external explosion overpressure. This paper investigated the correlation behavior between large-scale congestion and vent surface in a typical Chinese civil kitchen during natural gas explosion process and provided important support for understanding the mechanism of congestion on gas explosion process and the distribution of explosion hazards in a kitchen.

scholarly journals Effect of Congestion on Flow Field of Vented Natural Gas Explosion in a Kitchen

2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Lei Pang ◽  
Qianran Hu ◽  
Mengjie Jin ◽  
Kai Yang
Keyword(s):  
Natural Gas ◽  
Flow Field ◽  
Cross Section ◽  
Large Scale ◽  
Flame Structure ◽  
Small Scale ◽  
Gas Explosion ◽  
Cross Sectional ◽  
Surrounding Areas ◽  
The Impact

The process of gas explosion venting in a typical Chinese civil kitchen was investigated using computational fluid dynamics technology, focusing on the impact of the scale and cross-sectional characteristics of congestion, such as common furniture and electrical appliances, on the explosion flow-field parameters. An asymmetrical distribution of congestion will cause the uneven combustion of explosion flames in the kitchen. The flame will initially spread on one side of the room and then accelerate toward the surrounding areas, thereby increasing the risk of indoor gas explosion. The typical indoor overpressure change process can be divided into five stages, among which Stage V is found to be related to pseudoclosed combustion. Large-scale congestion has an obstructive effect on the explosion flow field, but it changes under certain conditions, while small-scale congestion only acts as a promoter. The flat congestion cross section helps maintain the stability of the flame structure, whereas the continuous and abrupt change of the congestion cross section can induce strong turbulent combustion. The research results provide a theoretical basis for the prevention and control of natural gas explosion hazards in civil kitchens from the perspective of congestion scale and cross-sectional mutation.

Effect of spark ignition location on the turbulent jet ignition characteristics in a lean burning natural gas engine

2022 ◽  
pp. 146808742110646
Author(s):  
Xue Yang ◽  
Yong Cheng ◽  
Qingwu Zhao ◽  
Pengcheng Wang ◽  
Jinbing Chen
Keyword(s):  
Natural Gas ◽  
Flow Field ◽  
Flame Propagation ◽  
Combustion Rate ◽  
Propagation Distance ◽  
Spark Ignition ◽  
Turbulent Jet ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Cylinder Flow

The Turbulent Jet Ignition is an effective concept to achieve stable lean burning for natural gas engines due to the multiple ignition sources, high ignition energy, and fast combustion rate. A variation of the ignition location has a non-negligible effect on the ignition performance of the TJI system. The present work aims to provide more details on this effect by numerical simulations. Both factors of the additional fuel supply to the pre-chamber and the in-cylinder flow field are taken into consideration in this study. A numerical model is built based on a lean burning natural gas engine and validated by experimental results. Five different spark ignition sources are equally arranged on the vertical axis of the pre-chamber, with different distances from the connecting orifices. Simulations are carried out under the same initial and boundary conditions except for the location of the ignition source. Combustion pressure, in-cylinder flow field, fuel mass fraction distribution, and heat release rate are analyzed to study the in-cylinder ignition and combustion process. The results show that a rotational flow and a non-uniform fuel distribution are formed in the pre-chamber during the compression stroke. The turbulent jet characteristics are significantly influenced by the coupling of two factors: the combustion rate inside the pre-chamber as well as the flame propagation distance from the ignition source to the connecting orifices. Rapid combustion rate and shorter flame propagation distance both lead to the earlier ejection of cold jets and hot jets. Among five ignition sources, the one located closest to the connecting orifices generates earlier hot jets with the highest mean velocity. The jets are more effective to ignite the lean mixture and could decrease the combustion duration of the main chamber.

scholarly journals A Study on the Instantaneous Turbulent Flow Field in a 90-Degree Elbow Pipe with Circular Section

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Shiming Wang ◽  
Cheng Ren ◽  
Yangfei Sun ◽  
Xingtuan Yang ◽  
Jiyuan Tu
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Flow Separation ◽  
Large Scale ◽  
Small Scale ◽  
Eddy Simulation ◽  
Dean Vortex ◽  
Instantaneous Flow Field ◽  
Instantaneous Pressure ◽  
Turbulent Flow Field

Based on the special application of 90-degree elbow pipe in the HTR-PM, the large eddy simulation was selected to calculate the instantaneous flow field in the 90-degree elbow pipe combining with the experimental results. The characteristics of the instantaneous turbulent flow field under the influence of flow separation and secondary flow were studied by analyzing the instantaneous pressure information at specific monitoring points and the instantaneous velocity field on the cross section of the elbow. The pattern and the intensity of the Dean vortex and the small scale eddies change over time and induce the asymmetry of the flow field. The turbulent disturbance upstream and the flow separation near the intrados couple with the vortexes of various scales. Energy is transferred from large scale eddies to small scale eddies and dissipated by the viscous stress in the end.

scholarly journals A study of the flow-field evolution and mixing in a planar turbulent jet using direct numerical simulation

2002 ◽  
Vol 450 ◽  
pp. 377-407 ◽  
Author(s):  
S. A. STANLEY ◽  
S. SARKAR ◽  
J. P. MELLADO
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Direct Numerical Simulation ◽  
Large Scale ◽  
Computational Study ◽  
Practical Interest ◽  
Small Scale ◽  
Mixing Process ◽  
Mean Velocity ◽  
Small Scales

Turbulent plane jets are prototypical free shear flows of practical interest in propulsion, combustion and environmental flows. While considerable experimental research has been performed on planar jets, very few computational studies exist. To the authors' knowledge, this is the first computational study of spatially evolving three-dimensional planar turbulent jets utilizing direct numerical simulation. Jet growth rates as well as the mean velocity, mean scalar and Reynolds stress profiles compare well with experimental data. Coherency spectra, vorticity visualization and autospectra are obtained to identify inferred structures. The development of the initial shear layer instability, as well as the evolution into the jet column mode downstream is captured well.The large- and small-scale anisotropies in the jet are discussed in detail. It is shown that, while the large scales in the flow field adjust slowly to variations in the local mean velocity gradients, the small scales adjust rapidly. Near the centreline of the jet, the small scales of turbulence are more isotropic. The mixing process is studied through analysis of the probability density functions of a passive scalar. Immediately after the rollup of vortical structures in the shear layers, the mixing process is dominated by large-scale engulfing of fluid. However, small-scale mixing dominates further downstream in the turbulent core of the self-similar region of the jet and a change from non-marching to marching PDFs is observed. Near the jet edges, the effects of large-scale engulfing of coflow fluid continue to influence the PDFs and non-marching type behaviour is observed.

Numerical study of external explosion characteristics induced by indoor natural gas vented explosion

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Lei Pang ◽  
Qianran Hu ◽  
Kai Yang
Keyword(s):  
Natural Gas ◽  
Design Methodology ◽  
Large Scale ◽  
Numerical Study ◽  
Outdoor Environment ◽  
Gas Explosion ◽  
Content Type ◽  
Gas Explosions ◽  
Explosion Overpressure ◽  
Vented Explosion

Purpose The purpose of this paper is to ascertain the harm to personnel and equipment caused by an external explosion during natural gas explosion venting. The external explosion characteristics induced by the indoor natural gas explosion are the focal points of the investigation. Design/methodology/approach Computational fluid dynamics technology was used to investigate the large-scale explosion venting process of natural gas in a 6 × 3 × 2.5 m room, and the characteristics of external explosion under different scaled vent size (Kv = Av/V2/3, 0.05, 0.08, 0.13, 0.18) were numerically analyzed. Findings When Kv = 0.08, the length and duration of the explosion fireball are 13.39 and 450 ms, respectively, which significantly expands the degree and range of high-temperature hazards. The suitable flow-field structure causes the external explosion overpressure to be more than twice that indoors, i.e. the natural gas explosion venting overpressure may be considerably more hazardous in an outdoor environment than inside a room. A specific range for the Kv can promote the superposition of outdoor rupture waves and explosion shock waves, thereby creating a new overpressure hazard. Originality/value Little attention has been devoted to investigating systematically the external explosion hazards. Based on the numerical simulation and the analysis, the external explosion characteristics induced by the indoor large-scale gas explosion were obtained. The research results are theoretically significant for mitigating the effects of external gas explosions on personnel and equipment.

Analysis of Crank Angle-Resolved Vortex Characteristics Under High Swirl Condition in a Spark-Ignition Direct-Injection Engine

2017 ◽  
Author(s):  
Fengnian Zhao ◽  
Penghui Ge ◽  
Hanyang Zhuang ◽  
David L. S. Hung
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
High Speed ◽  
Large Scale ◽  
Early Stage ◽  
Direct Injection ◽  
Spark Ignition ◽  
Small Scale ◽  
Vortex Center ◽  
Intake Stroke

In-cylinder air flow structure makes significant impacts on fuel spray dispersion, fuel mixture formation, and flame propagation in spark ignition direct injection (SIDI) engines. While flow vortices can be observed during the early stage of intake stroke, it is very difficult to clearly identify their transient characteristics because these vortices are of multiple length scales with very different swirl motion strength. In this study, a high-speed time-resolved 2D particle image velocimetry (PIV) is applied to record the flow structure of in-cylinder flow field along a swirl plane at 30 mm below the injector tip. First, a discretized method using flow field velocity vectors is presented to identify the location, strength, and rotating direction of vortices at different crank angles. The transients of vortex formation and dissipation processes are revealed by tracing the location and motion of the vortex center during the intake and compression strokes. In addition, an analysis method known as the wind-rose diagram, which is implemented for meteorological application, has been adopted to show the velocity direction distributions of 100 consecutive cycles. Results show that there exists more than one vortex center during early intake stroke and their fluctuations between each cycle can be clearly visualized. In summary, this approach provides an effective way to identify the vortex structure and to track the motion of vortex center for both large-scale and small-scale vortices.

Application of Adaptive Control to Reduce Cyclic Dispersion Near the Lean Limit in a Small-Scale, Natural Gas Engine

2004 ◽  
Author(s):  
K. Dean Edwards ◽  
Robert M. Wagner
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Large Scale ◽  
Small Scale ◽  
Target Point ◽  
Combustion Dynamics ◽  
Current Cycle ◽  
History Of ◽  
Lean Limit ◽  
Prediction Strategy

Predictive feedback control is applied to achieve reduction in cyclic dispersion in an analytical, lean, spark-ignition model and a two-cylinder, four-stroke, natural gas Kohler Command 25 engine operating at lean conditions. Recent observations of the combustion dynamics are used to define a desired target point for control and to predict future combustion events which may stray from the target point. Fueling perturbations are applied to steer the system back toward the desired behavior. Overall control perturbations are constrained to maintain a constant average fuel-to-air ratio. We present two methods for obtaining the prediction of future combustion events. In the first method, the recent history of cycle heat release is used to construct an adaptive, low-order map which relates the current-cycle heat release to the next-cycle heat release. The second method uses symbolic analysis to determine the relative frequency of successive-cycle combustion events and predict the most probable successor to the current cycle. Results are presented which show a moderate reduction in cycle-to-cycle variation near the lean limit in both the model and the engine. Similarities in behavior have been shown to exist-ignition engines suggesting that a similar prediction strategy could be successfully applied to control cyclic dispersion in large-scale reciprocating engines.

Development of 7%Ni-TMCP Steel Plate for LNG Storage Tanks

2011 ◽  
Author(s):  
Ryuichi Ando ◽  
Kazushige Arimochi ◽  
Tomoya Kawabata ◽  
Kazushi Onishi ◽  
Takahiro Kamo ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Natural Gas ◽  
Large Scale ◽  
Steel Plate ◽  
Physical And Mechanical Properties ◽  
Rare Metal ◽  
Small Scale ◽  
Chemical Compositions ◽  
Nickel Steel ◽  
Storage Tanks

Demand of natural gas continues to increase in the recent years due to the rise of environmental issue and the drastic increase of crude oil price. These events led to the increase of constructions of Liquefied Natural Gas (LNG) storage tanks worldwide. The inner tank material for above ground LNG storage tanks have mostly been made of a 9% nickel steel plate over the last 50 years as it has excellent mechanical properties under the cryogenic temperature of −160deg-C. During this period, the LNG storage tanks made of 9%Ni steel plate have been operated safely at the many LNG export and import terminals in the world. Meanwhile, technologies of steel making, refinement, design, analysis, welding and inspection have been improved significantly and enabled enlarging volumetric capacity of the tank 2–3 times. There was a tendency for nickel price to increase in recent years. In such a circumstance lowering Ni content has focused attention on the 9%Ni steel as nickel is an expensive and valuable rare metal and a 7%Ni steel plate was eventually researched and developed by optimizing the chemical compositions and applying Thermo-Mechanical Controlled Process (TMCP). As a result, it was demonstrated that 7%Ni-TMCP steel plate had excellent physical and mechanical properties equivalent to those of 9%Ni steel plate. In order to evaluate fitness of the 7%Ni-TMCP steel plate and its weld for LNG storage tanks a series of testing was conducted. Several different plate thicknesses, i.e. 6,10,25,40 and 50 mm, were chosen to run large scale fracture toughness tests including duplex ESSO tests, cruciform wide plate tests as well as small scale tests. It was concluded that the 7%Ni-TMCP steel plate warrants serious consideration for use in LNG storage tanks. This paper reports details of the research and development of the 7%Ni-TMCP steel plate.

scholarly journals Reynolds number and wind tunnel wall effects on the flow field around a generic UHBR engine high-lift configuration

2020 ◽  
Vol 11 (4) ◽  
pp. 1009-1023 ◽  
Author(s):  
Junaid Ullah ◽  
Aleš Prachař ◽  
Miroslav Šmíd ◽  
Avraham Seifert ◽  
Vitaly Soudakov ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Flow Field ◽  
Test Section ◽  
Large Scale ◽  
Scale Model ◽  
Small Scale ◽  
Wall Effects ◽  
Tunnel Wall ◽  
High Lift

Abstract RANS simulations of a generic ultra-high bypass ratio engine high-lift configuration were conducted in three different environments. The purpose of this study is to assess small scale tests in an atmospheric closed test section wind tunnel regarding transferability to large scale tests in an open-jet wind tunnel. Special emphasis was placed on the flow field in the separation prone region downstream from the extended slat cut-out. Validation with wind tunnel test data shows an adequate agreement with CFD results. The cross-comparison of the three sets of simulations allowed to identify the effects of the Reynolds number and the wind tunnel walls on the flow field separately. The simulations reveal significant blockage effects and corner flow separation induced by the test section walls. By comparison, the Reynolds number effects are negligible. A decrease of the incidence angle for the small scale model allows to successfully reproduce the flow field of the large scale model despite severe wind tunnel wall effects.

scholarly journals Numerical simulation of leakage flow field and acoustic characteristics for safety valve

2021 ◽  
Vol 336 ◽  
pp. 01007
Author(s):  
Fan Qian ◽  
Minghui Hu
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Pressure Fluctuation ◽  
Large Scale ◽  
Safety Valve ◽  
Sound Field ◽  
Wall Pressure ◽  
Small Scale ◽  
Acoustic Analogy ◽  
Wall Pressure Fluctuation

Aiming at the internal leakage problem of spring type nuclear safety valve at the sealing surface, the flow field and sound field characteristics at the leakage height of 0.5mm between the valve disc and the valve seat sealing surface were studied, and the numerical simulation was carried out based on large eddy simulation(LES) and mohring acoustic analogy method, and compare the effects of acoustic wall pressure fluctuation(AWPF) and turbulent wall pressure fluctuation(TWPF) as the excitation source on the external sound field of the valve. The simulation results show that: the change gradient of velocity field and pressure field at the leakage port of safety valve is significant and form vortices of different sizes. The small-scale vortices are mainly in the leakage port, while the large-scale vortices mainly exist in the flow channel; When the valve is leaking, the noise is mainly dominated by high-pressure injection noise, its spectrum curve shows wide-band characteristics, and the external noise of the valve is mainly caused by AW P F. The above research results can provide a theoretical basis for the safety valve online detection method.

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