scholarly journals Numerical Study on Dynamical Structures and the Destratification of Vertical Turbulent Jets in Stratified Environment

Water ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 2085
Author(s):  
Xuan Huang ◽  
Ling-ling Wang ◽  
Jin Xu
Keyword(s):  
Internal Wave ◽  
Horizontal Plane ◽  
Numerical Study ◽  
Turbulent Jets ◽  
Threshold Value ◽  
Pollutant Emission ◽  
Dimensionless Time ◽  
Gaussian Profile ◽  
Dimensionless Analysis ◽  
The Law

The law of pollutant emission and diffusion in stratified waters is a common issue. In this paper, numerical study on the interaction between vertical turbulent jets and the pycnocline is carried out to study the problems of jet’s emission through the large eddy simulation (LES). A trigonometric function disturbance (TFD) method is developed to ensure the velocity distribution of the jet in the horizontal plane yield to Gaussian profile. Numerical simulations are carried out in the range of 1.11 < Frp < 4.77, corresponding to 1393 < Rep < 5979, where the Froude number Frp and the Reynolds number Rep are defined at the entrance of pycnocline. The coherent structure and internal waves are observed at the pycnocline during the process of jets impinging. After the impingement, the destratification effects can be found. It can be found that Frp = 3 is a threshold value for the interaction between jets and the pycnocline. When Frp > 3, the interaction becomes intensely. Furthermore, the fitting formula of the radial momentum flux dissipation rate that is used to describe the decay of energy contained by the jets during the impinging process, is established through the dimensionless analysis. As a result, the influence range of the jet on the horizontal plane can be evaluated by Rep. It is also found that the destratification of jets is mainly affected by the velocity of the internal wave induced by jets. In addition, by employing the dimensionless time T related to that velocity, the law of destratification varies with dimensionless time is obtained, which can be summarized as follows: Due to the influence of the first internal wave, the thickness of the pycnocline increases rapidly and reaches a critical value at T = 1.4, after that, the increase of the thickness of the pycnocline becomes linear.

Numerical Study of the Mean and Filtered Characteristics of Turbulent Jets Impinging on Convex and Flat Surfaces Using LES

2012 ◽  
Author(s):  
Adra Benhacine ◽  
Zoubir Nemouchi ◽  
Lyes Khezzar ◽  
Nabil Kharoua
Keyword(s):  
Convex Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Scale Model ◽  
Wall Jet ◽  
Potential Core ◽  
Flat Surfaces ◽  
Free Jet ◽  
Eddy Simulation

A numerical study of a turbulent plane jet impinging on a convex surface and on a flat surface is presented, using the large eddy simulation approach and the Smagorinski-Lilly sub-grid-scale model. The effects of the wall curvature on the unsteady filtered, and the steady mean, parameters characterizing the dynamics of the wall jet are addressed in particular. In the free jet upstream of the impingement region, significant and fairly ordered velocity fluctuations, that are not turbulent in nature, are observed inside the potential core. Kelvin-Helmholtz instabilities in the shear layer between the jet and the surrounding air are detected in the form of wavy sheets of vorticity. Rolled up vortices are detached from these sheets in a more or less periodic manner, evolving into distorted three dimensional structures. Along the wall jet the Coanda effect causes a marked suction along the convex surface compared with the flat one. As a result, relatively important tangential velocities and a stretching of sporadic streamwise vortices are observed, leading to friction coefficient values on the curved wall higher than those on the flat wall.

Generation of Efficient Terahertz Radiation by Relativistic Self-Focusing of A Cosh-Gaussian Laser Beam in A Magnetized Plasma

2021 ◽  
Author(s):  
Gunjan Purohit ◽  
Bineet Gaur ◽  
Pradeep Kothiyal ◽  
Amita Raizada
Keyword(s):  
Laser Beam ◽  
Numerical Study ◽  
The Self ◽  
Magnetized Plasma ◽  
Thz Radiation ◽  
Gaussian Laser Beam ◽  
Plasma Parameters ◽  
Gaussian Profile ◽  
Self Focusing ◽  
Incident Laser Intensity

Abstract This paper presents a scheme for the generation of terahertz (THz) radiation by self-focusing of a cosh-Gaussian laser beam in the magnetized and rippled density plasma, when relativistic nonlinearity is operative. The strong coupling between self-focused laser beam and pre-existing density ripple produces nonlinear current that originates THz radiation. THz radiation is produced by the interaction of the cosh-Gaussian laser beam with electron plasma wave under the appropriate phase matching conditions. Expressions for the beamwidth parameter of cosh-Gaussian laser beam and the electric vector of the THz radiation have been obtained using higher-order paraxial theory and solved numerically. The self-focusing of the cosh-Gaussian laser beam and its effect on the generated THz amplitude have been studied for specific laser and plasma parameters. Numerical study has been performed on various values of the decentered parameter, incident laser intensity, magnetic field, and relative density. The results have also been compared with the paraxial region as well as the Gaussian profile of laser beam. Numerical results suggest that the self-focusing of the cosh-Gaussian laser beam and the amplitude of THz radiation increase in the extended paraxial region compared to the paraxial region. It is also observed that the focusing of the cosh-Gaussian laser beam in the magnetized plasma and the amplitude of the THz radiation increases at higher values of the decentered parameter.

A Numerical Study of the Fixed-Threshold Criterion for Expressing Transient Stability Constraints in Optimal Power Flow

2015 ◽  
Vol 781 ◽  
pp. 379-383
Author(s):  
Warut Suampun
Keyword(s):  
Power Flow ◽  
Optimal Power Flow ◽  
Transient Stability ◽  
Numerical Study ◽  
Threshold Value ◽  
Computing System ◽  
Threshold Values ◽  
Optimal Power ◽  
Threshold Criterion ◽  
Fixed Threshold

A numerical study of the widely used fixed-threshold criterion for expressing transient stability constraints in optimal power flow (TSCOPF) is conducted. Based on a stability-region framework, a more accurate expression of transient stability constraint in TSCOPF is presented. A method for computing system exact threshold values is proposed and employed for the study of threshold values under different conditions. It is shown via numerical results on the WSCC9 and IEEE145 systems that the exact threshold value for each system and contingency is in fact not a constant, and can vary greatly depending on several factors such as types of contingency, loading conditions, and network topology.

scholarly journals Experimental and Numerical Study of the Coanda Effect Used to Reduce Self-Sustained Tones

2002 ◽  
Author(s):  
C. Allery ◽  
S. Gue´rin ◽  
A. Hamdouni ◽  
A. Sakout
Keyword(s):  
Horizontal Plane ◽  
Numerical Study ◽  
Coanda Effect ◽  
Inclined Plane ◽  
Flow Configuration ◽  
Large Hysteresis ◽  
Dimensional Dynamical System ◽  
Coandǎ Effect ◽  
Low Dimensional ◽  
Proper Orthogonal

We present in this paper an experimental and numerical study about the Coanda effect which causes the sudden reattachment of a jet to an inclined plane. This phenomenon induces a large hysteresis loop, which can be used to reduce the noise produced by an airflow crossing two diaphragms in tandem inside a duct. The angle of the inclined wall with horizontal plane and the flow velocity are the two main parameters studied here. With the aim of doing optimal control, we propose to construct for this flow configuration a low-dimensional dynamical system with a basis issued from a Proper Orthogonal Decomposition.

scholarly journals Numerical Study for Experiment on Wave Pattern of Internal Wave and Surface Wave in Stratified Fluid

2019 ◽  
Vol 33 (3) ◽  
pp. 236-244
Author(s):  
Ju-Han Lee ◽  
Kwan-Woo Kim ◽  
Kwang-Jun Paik ◽  
Won-Cheol Koo ◽  
Yeong-Gyu Kim
Keyword(s):  
Surface Wave ◽  
Internal Wave ◽  
Numerical Study ◽  
Wave Pattern ◽  
Stratified Fluid

EXPERIMENTAL AND NUMERICAL STUDY OF THERMAL ANALYSIS OF HIGH-SPEED FRICTION BRAKING SYSTEM

2011 ◽  
Vol 10 (01) ◽  
pp. 135-142
Author(s):  
CHUNMEI ZHANG ◽  
YONGFENG LI
Keyword(s):  
Thermal Analysis ◽  
Friction Surface ◽  
High Speed ◽  
Material Selection ◽  
Numerical Study ◽  
Friction Pair ◽  
Maximum Temperature ◽  
Dimensionless Time ◽  
Braking System ◽  
Friction Braking System

Thermal analysis can be used as one of the basis for the friction pair material selection in high-speed friction braking system. In this study, the experimental results showed that surface temperature could be reduced by increasing the radius of the friction disk or thermal conductivity coefficient of disk material with stable braking; In the early stage of long braking, the temperature on the friction surface rises rapidly, but further braking does not lead to a significant rise in temperature; In the case of short braking, there is not enough time for the friction surface to reach the critical temperature, and the disk surface reaches the maximum temperature at the end of braking. During long braking, the dimensionless time capacity of the friction surface reaching the highest temperature is F0 ≈ 0.1F0s.

Detailed Study of Front Module for Low-Emission Combustor

2020 ◽  
Author(s):  
A. Vasilyev ◽  
V. Zakharov ◽  
O. Chelebyan ◽  
O. Zubkova
Keyword(s):  
Experimental Data ◽  
Numerical Study ◽  
Flame Structure ◽  
Combustion Efficiency ◽  
Liquid Fuels ◽  
Pollutant Emission ◽  
Additional Information ◽  
Low Emission ◽  
Wide Range ◽  
To Receive

Abstract At the ASME Turbo Expo 2018 conference held in Oslo (Norway) on the 11th-15th of June 2018, the paper GT2018-75419 «Experience of Low-Emission Combustion of Aviation and Bio Fuels in Individual Flames after Front Mini-Modules of a Combustion Chamber» was published. This paper continues the studies devoted to the low-emission combustion of liquid fuels in GTE combustors. The paper presents a description of more detailed studies of the front module with a staged pneumatic fuel spray. The aerodynamic computations of the front module were conducted, and the disperse characteristics of the fuel-air spray were measured. The experimental research was carried out in two directions: 1) probing of the 3-burner sector flame tube at the distance of one third of its length (temperature field and gas sampling); 2) numerical study of the model combustor with actual arrangement of the modules in the dome within a wide range of fuel-air ratio. The calculated and experimental data of velocity field behind the front module were compared. And new data about the flame structure inside the test sector were obtained. Experimental data confirm the results of preliminary studies of the 3-burner sector: combustion efficiency is higher than 99.8%, EiNOx is at the level of 2–3 g/fuel kg at the combustor inlet air temperature of 680K and fuel-air ratio of 0.0225. The conducted research allowed to receive additional information on the influence of some design units on the pollutant emission and to estimate the different elements of computational methods for simulation of a low-emission combustor with a multi-atomizer dome.

scholarly journals A numerical study of confined turbulent jets for homogeneous combustion with oxygen enrichment

Fuel ◽  
2020 ◽  
Vol 261 ◽  
pp. 116449 ◽  
Author(s):  
Kumar Aanjaneya ◽  
Weiyu Cao ◽  
Yawei Chen ◽  
Claus Borgnakke ◽  
Arvind Atreya
Keyword(s):  
Numerical Study ◽  
Turbulent Jets ◽  
Oxygen Enrichment ◽  
Homogeneous Combustion
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