A Stochastic Immersed Model of Breakup Characteristics in Dense Air Atomization Flow Field

2020 ◽  
Author(s):  
Tian Deng ◽  
Xingming Ren ◽  
Yaxuan Li
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Large Scale ◽  
Gas Flow ◽  
Liquid Core ◽  
Average Diameter ◽  
Simulation Method ◽  
Spray Angle ◽  
Random Structure ◽  
Momentum Ratio

Abstract For the low-speed liquid injected into the high-speed strong turbulent gas flow in the same direction, the atomization is a transient-intensive spray, and there are many factors affecting and controlling the atomization. In this paper, the distribution and characteristics of the liquid breakup in the air atomized flow field are analyzed. A stochastic immersed model to simulate the liquid core is developed, in which, the liquid core is regarded as an immersed porous medium with a random structure, and the probability of existence is used to simulate the position of the liquid core. The initial fragmentation mechanism of the air blast atomization is applied as the global variables of the stochastic process. Using the above stochastic immersed model, combined with the Large Eddy Simulation method, the numerical simulation of the downstream flow field of a coaxial jet air atomizing nozzle is carried out. Additional force is added to the momentum equation in the LES model. Instantaneous air velocity at the air-liquid interface is characterized by instantaneous liquid phase velocity at the same time. The size of the initial atomized droplet satisfies a probability distribution, and once the large droplets are formed, the Lagrangian method is used to track the droplets. The comparison between the simulation results and the experimental results shows that this stochastic immersed model can quickly capture the information of length and position of the liquid nucleus. When the gas-liquid momentum ratio M is 3∼10000, the liquid core length can be predicted more accurately. When M>10, the prediction result is much better than phenomenological model. This model is capable of capturing flow field structures such as recirculation zones and large-scale vortices. The results of initial spray angle from experiment expression give slightly better agreement with this model. Increasing the momentum ratio leads to decreasing of the initial spray angle. The particle size of the droplets near the nozzle can be accurately predicted, especially when the gas velocity is large (bigger than 60 m/s), and the average diameter prediction error of the droplets is less than 10%.

A real-time control method-based simulation for high-speed trains on large-scale rail network

2017 ◽  
Vol 28 (10) ◽  
pp. 1750126 ◽  
Author(s):  
Yutong Liu ◽  
Chengxuan Cao ◽  
Yaling Zhou ◽  
Ziyan Feng
Keyword(s):  
Real Time ◽  
Traffic Flow ◽  
High Speed ◽  
Large Scale ◽  
Simulation Method ◽  
Real Time Control ◽  
Rail Network ◽  
Time Control ◽  
High Speed Trains ◽  
Rail Traffic

In this paper, an improved real-time control model based on the discrete-time method is constructed to control and simulate the movement of high-speed trains on large-scale rail network. The constraints of acceleration and deceleration are introduced in this model, and a more reasonable definition of the minimal headway is also presented. Considering the complicated rail traffic environment in practice, we propose a set of sound operational strategies to excellently control traffic flow on rail network under various conditions. Several simulation experiments with different parameter combinations are conducted to verify the effectiveness of the control simulation method. The experimental results are similar to realistic environment and some characteristics of rail traffic flow are also investigated, especially the impact of stochastic disturbances and the minimal headway on the rail traffic flow on large-scale rail network, which can better assist dispatchers in analysis and decision-making. Meanwhile, experimental results also demonstrate that the proposed control simulation method can be in real-time control of traffic flow for high-speed trains not only on the simple rail line, but also on the complicated large-scale network such as China’s high-speed rail network and serve as a tool of simulating the traffic flow on large-scale rail network to study the characteristics of rail traffic flow.

scholarly journals Synthesis of Silicon Nanoparticles in a Novel CO2 Laser Pyrolysis Reactor With an Elongated Reaction Zone

2020 ◽  
Author(s):  
Seok-Ho Maeng ◽  
Hakju Lee ◽  
Seongbeom Kim
Keyword(s):  
Reaction Zone ◽  
Large Scale ◽  
Gas Flow ◽  
Silicon Nanoparticles ◽  
Nanoparticle Synthesis ◽  
Average Diameter ◽  
Laser Pyrolysis ◽  
Pyrolysis Reactor ◽  
The Masses ◽  
Focusing Lens

Abstract We demonstrated silicon nanoparticle synthesis using a novel CO2 laser pyrolysis reactor. The reactor was designed to have an elongated reaction zone more than 10 times longer than conventional laser pyrolysis systems. Such elongation was achieved by aligning the laser beam and precursor gas stream. SiH4 gas was used to synthesize the silicon nanoparticles. The yield of the nanoparticles was 40.9%, as calculated by comparing the masses of the synthesized nanoparticles and precursor gas used. Silicon nanoparticles synthesized by using a typical reactor with identical gas flow rate conditions and without a focusing lens had a nanoparticle yield of 1.7%, which was far smaller than for the new reactor. The average diameter of as-synthesized silicon nanoparticles was 26.7 nm. Considering that high power CO2 lasers are often used for large scale nanoparticle production by laser pyrolysis, our proposed reactor serves as a proof of concept that demonstrates its potential for large scale nanoparticle synthesis.

Optimze the Structure of Impeller for Stirred Bioreactor

2013 ◽  
Vol 694-697 ◽  
pp. 148-153 ◽  
Author(s):  
Li Kuan Zhu ◽  
Bo Yan Song ◽  
Zhen Long Wang ◽  
Yu Kui Wang
Keyword(s):  
Fluid Dynamics ◽  
Flow Field ◽  
Shear Force ◽  
Large Scale ◽  
Cfd Simulation ◽  
Simulation Method ◽  
Stirred Bioreactor ◽  
Anticlockwise Rotation ◽  
Computational Fluid Dynamics Cfd ◽  
Large Scale Culture

This paper mainly makes comparative analysis on four main types of blade in stirred bioreactor by Computational Fluid Dynamics(CFD) simulation. Firstly we establish simulation method suited for stirred bioreactor, then simulate the velocity and shear force of flow field in the bioreactor. No matter from flow field mixing or shear force aspect, Elephant Ear blades is the most suitable for cell large scale culture. At last, it optimizes the installation method and angle of Elephant Ear blades. It concludes that anticlockwise rotation and 45°installation angle is the optimum.

Investigation of the instability mechanisms in a turbocharger centrifugal compressor with a vaneless diffuser by means of unsteady simulations

2016 ◽  
Vol 231 (11) ◽  
pp. 1558-1567 ◽  
Author(s):  
Xinqian Zheng ◽  
Anxiong Liu ◽  
Zhenzhong Sun
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Simulation Method ◽  
Great Accuracy ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Low Velocity

The stable-flow range of a compressor is predominantly limited by surge and stall. In this paper, an unsteady simulation method was employed to investigate the instability mechanisms of a high-speed turbocharger centrifugal compressor with a vaneless diffuser. In comparison with the variation in the pressure obtained by dynamic experiments on the same compressor, unsteady simulations show a great accuracy in representing the stall behaviour. The predicted frequency of the rotating stall is 22.5% of the rotor frequency, which agrees with to the value for the high-frequency short-term rotating stall obtained experimentally. By investigating the instability of the flow field, it is found that the unstable flow of the turbocharger compressor at high rotational speeds is caused by the tip clearance leakage flow and the ‘backflow vortices’ originating from the interaction of the incoming flow and the backflow in the tip region of the passages. The asymmetric volute helps to induce the occurrence of stall in certain impeller passages because it generates an asymmetric flow field. The high-pressure low-velocity area from the 180° circumferential position to the 270° circumferential position is dominant and strengthens the backflow at the trailing edge of the impeller, finally triggering the stall.

Numerical Simulation of the Flow in a Large-Scale Thrust Bearing

2010 ◽  
Author(s):  
Hong-Jie Wang ◽  
Ru-Zhi Gong ◽  
De-Ping Lu ◽  
Zhong-De Wu ◽  
Feng-Chen Li
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Large Scale ◽  
Thrust Bearing ◽  
Cfd Simulation ◽  
Internal Flow ◽  
Heat Radiation ◽  
Heavy Load ◽  
Cfd Method ◽  
Water Turbines

Thrust bearing is a key component of large-scale water turbine. It closely relates to the efficiency of large-scale water turbines, and even determines whether the large-scale turbine can operate normally. With the development of the capacitance of water turbines, thrust bearing will develop to the direction of high speed and heavy load. The structure, strength, lubrication and the characteristic of heat radiation of large-scale thrust bearing were often researched in the past. To study the flow condition of the large-scale thrust bearing and analyze the load characteristics, CFD simulation was carried out on the model of thrust bearing. In this study, CFD method was used to simulate the internal flow field of the large-scale thrust bearing. The model researched was a thrust bearing for 1000MW water turbines. The diameter of the thrust bearing was over 5.8 meters, and the maximum thrust load of the bearing can reach to 60MN. The thin gap between the runner and the pad was usually neglected in the published CFD calculations of thrust bearing. But the thin gap was taken into account in this investigation. 1/12 of the model was used as the computational field and periodic boundary was used in the calculation. The standard κ-ε turbulence model was used to simulate the thrust bearing model, and the flow field in the thrust bearing was obtained. The thin gap between the runner and the pad is a wedge. The pressure and velocity distribution in the thrust bearing and thin gap was calculated respectively with conditions of different thin gaps and different rotational speeds of runner. After that, the relationship between carrying capacity and the size of clearance or the speed of the runner through analyzing the data has been obtained from the results of the calculation.

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.

Research on Numerical Simulation Method for 3D Complex Flow in Rotating Machinery

2012 ◽  
Vol 226-228 ◽  
pp. 52-55
Author(s):  
Guang Yu Du ◽  
Zhen Tan ◽  
Wei An ◽  
De Сhun Ba
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Gas Flow ◽  
Turbulence Models ◽  
Simulation Method ◽  
Rotating Machinery ◽  
Field Analysis ◽  
Complex Flow ◽  
Structure Interaction ◽  
Numerical Simulation Method

A numerical simulation method with gas-structure interaction to analyze 3D complex flow in rotating machinery was presented and the effects with different aerodynamic turbulence model for gas-structure interaction was also presented. The blades are an important component in rotating machinery. Gas flow is unsteady three-dimensional turbulence motion with transient and anisotropic. Then the gas flow and the vibration of rotating blades interfere with each other, resulting in a complex coupling effect. It affects the machine efficiency directly. For discussing the effects on flow field of the coupling field, the blade model was built. And flow around the blades was simulated by gas-structure interaction with three turbulence models respectively. The turbulence models were standard κ-ε, renormalization group κ-ε and Smagorinsky LES. A feasible method was provided for flow field analysis in rotating machinery.

A Method for Solving Problems of Irrotational Gas Flow by Means of High-Speed Digital Computers

1957 ◽  
Vol 24 (4) ◽  
pp. 497-500
Author(s):  
Toyoki Koga
Keyword(s):  
Flow Field ◽  
Analytical Methods ◽  
High Speed ◽  
Gas Flow ◽  
Fundamental Equation ◽  
Numerical Procedure ◽  
The State ◽  
Two Dimensional ◽  
Perfect Gas ◽  
Irrotational Flow

Abstract A numerical procedure is proposed for solution of certain problems in steady gas flow where subsonic, sonic, and supersonic regions appear simultaneously. The difficulties that occur in analytical methods for taking into account the differences of the type of the fundamental equation (elliptic, parabolic, hyperbolic) are avoided. Given a streamline and the state of the gas along that streamline, the co-ordinates of the neighboring streamline and the state of the gas along it can be computed. The procedure can be applied successively to cover a flow field. The method is described in detail for two-dimensional, steady, irrotational flow (without shocks) of a perfect gas, and an example is given.

Numerical Simulation Research of Air-Assisted Atomizer Internal Gas Flow Field Based on Fluent

2014 ◽  
Vol 599-601 ◽  
pp. 377-380
Author(s):  
Qiao Li ◽  
Ya Yu Huang
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Total Pressure ◽  
High Speed ◽  
Gas Flow ◽  
Static Pressure ◽  
Mutual Influence ◽  
Simulation Research ◽  
Simulation Calculation ◽  
Gas Flow Field

The numerical simulation calculation of air-assisted atomizer internal gas flow field is done, the distribution and changes of the nozzle inside flow field total pressure, velocity, and dynamic and static pressure are analyzed. The analysis shows that the total pressure loss is less; due to the effect of gas viscous, the high-speed air flow is formed vortex flow near the outlet nozzle and the mutual influence between the dynamic and static pressure. A new way is supported for optimizing the nozzle structure according to these studies.

Sign in / Sign up

Export Citation Format

Share Document