• Title/Summary/Keyword: Turbulent Diffusion

Search Result 268, Processing Time 0.031 seconds

Comparison study of turbulent diffusion coefficient using Smagorinsky method and 2-level method (Smagorinsky method와 2-level method를 이용한 난류 확산계수의 비교 연구)

  • 이화운;오은주;정우식;최현정;임주연
    • Journal of Environmental Science International
    • /
    • v.11 no.7
    • /
    • pp.679-686
    • /
    • 2002
  • Turbulence greatly influence on atmospheric flow field. In the atmosphere, turbulence is represented as turbulent diffusion coefficients. To estimate turbulent diffusion coefficients in previous studies, it has been used constants or 2-level method which divides surface layer and Ekman layer. In this study, it was introduced Smagorinsky method which estimates turbulent diffusion coefficient not to divide the layer but to continue in vertical direction. We simulated 3-D flow model and TKE equation applied turbulent diffusion coefficients using two methods, respectively. Then we showed the values of TKE and the condition of each term to TKE. The results of Smagorinsky method were reasonable. But the results of 2-level method were not reasonable. Therefor, it had better use Smagorinsky method to estimate turbulent diffusion coefficients. We are expected that if it is developed better TKE equation and model with study of computational method in several turbulent diffusion coefficients for reasonably turbulent diffusion, we will able to predict precise wind field and movements of air pollutants.

THERMAL CONDUCTION IN MAGNETIZED TURBULENT GAS

  • CHO JUNGYEON;LAZARIAN A.
    • Journal of The Korean Astronomical Society
    • /
    • v.37 no.5
    • /
    • pp.557-562
    • /
    • 2004
  • We discuss diffusion of particles in turbulent flows. In hydrodynamic turbulence, it is well known that distance between two particles imbedded in a turbulent flow exhibits a random walk behavior. The corresponding diffusion coefficient is ${\~}$ ${\upsilon}_{inj}{\iota}_{turb}$, where ${\upsilon}_{inj}$ is the amplitude of the turbulent velocity and ${\iota}_{turb}$ is the scale of the turbulent motions. It Is not clear whether or not we can use a similar expression for magnetohydrodynamic turbulence. However, numerical simulations show that mixing motions perpendicular to the local magnetic field are, up to high degree, hydrodynamical. This suggests that turbulent heat transport in magnetized turbulent fluid should be similar to that in non-magnetized one, which should have a diffusion coefficient ${\upsilon}_{inj}{\iota}_{turb}$. We review numerical simulations that support this conclusion. The application of this idea to thermal conductivity in clusters of galaxies shows that this mechanism may dominate the diffusion of heat and may be efficient enough to prevent cooling flow formation when turbulence is vigorous.

Study on the Turbulent Edge Propagation Speed of a Lifted Diffusion Flame in Turbulent Mixing Layer (난류 혼합층 확산화염에서 부상선단의 난류전파속도에 대한 연구)

  • Kim, Jun-Hong;Chung, S.H.;Ahn, K.Y.;Kim, J.S.
    • 한국연소학회:학술대회논문집
    • /
    • 2004.11a
    • /
    • pp.55-61
    • /
    • 2004
  • Leading front of a lifted diffusion flame in turbulent mixing layer was investigated in order to find a appropriate definition of the turbulent edge propagation speed. The turbulent lifted diffusion flame was simulated by employing the flame hole dynamics combined with level-set method which yields a temporally evolving turbulent extinction process. By tracing the leading front locations of the temporal flame edges, temporal variations of the liftoff height, local flow velocity, and edge propagation speed at the leading front were investigated and they demonstrated the flame-stabilization condition of the turbulent lifted flame. Finally, a turbulent edge propagation speed was defined and its temporal variation from the simulation was discussed.

  • PDF

A Study on the Soot Measurement in Laminar and Turbulent Diffusion Flame Using the Laser Diagnostics (광계측 기법을 이용한 층류 및 난류 확산 화염에서의 매연 측정에 관한 연구)

  • Lee, Jun-Yong;Han, Yong-Taik;Lim, Jun-Won;Min, Kyoung-Doug
    • Proceedings of the KSME Conference
    • /
    • 2008.11b
    • /
    • pp.3073-3078
    • /
    • 2008
  • In this study to find out the amount of soot, LII method, which utilizes a laser, was used in laminar diffusion flame and based upon the temperature and soot measured from the turbulent Diesel diffusion flame in the constant-volume chamber using the two-color method. Through these experiments, we could know that the LII signal is generally proportional to the soot amount in a laminar diffusion flame. And we could acquire the temperature and soot using the two-color method in a turbulent Diesel diffusion flame effectively. In addition to, this experiment revealed that the KL factor was high on parts of the chamber where the temperature dropped. On the other hand, the KL factor was low where the temperature increased rapidly. Also, it was possible to measure the highest temperature of a turbulent Diesel diffusion flame is approximately 2300K.

  • PDF

Numerical Study of Shear-Enhanced Turbulent Diffusion (전단 증진된 난류확산의 수치적 연구)

  • Lee, Chang-Hun;Choe, Jae-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.25 no.7
    • /
    • pp.944-951
    • /
    • 2001
  • The purpose of this study is to investigate the effect of shear on turbulent diffusion. Turbulent Couette flows at low Reynolds number are numerically simulated using a Lagrangian PDF method. Flow field and particle trajectories are computed and analyzed in detail. Statistics for particle dispersion obtained from numerical simulations is compared with the classical scaling relations for dispersion in a shear flow.

An Experimental Study About The Intermittent Flow Field in The Transition Region of a Turbulent Round Jet (발달하는 원형제트의 간헐적 유동에 관한 실험적 연구)

  • 김숭기;조지룡;정명균
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.14 no.1
    • /
    • pp.230-240
    • /
    • 1990
  • An exprimental research has been carried out to find the intermittent flow pattern in the transition region of a turbulent round jet in order to elucidate detailed turbulence structure and to accumulate basic data necessary for computational turbulence modelling. Turbulent signals were processed digitally to obtain conventional or conditional velocity components. The high-order conditional correlations obtained in this study showed similar trends as those of other free shear flows. It was found that the non-turbulent fluid contributes negligibly to the turbulent kinetic energy production and its diffusive transport and that the diffusion by bulk convection has the same order of magnitude as the gradient diffusion in the free boundary region. The statistical analyses such as flatness factor, skewness factor and probability density functions of turbulent and non-turbulent zone durations have also been performed.

Experimental Study on Combustion Noise Characteristics in Turbulent Jet Diffusion Flames (난류 제트확산화염의 연소소음 특성에 관한 실험연구)

  • 김호석;오상헌
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.18 no.5
    • /
    • pp.1253-1263
    • /
    • 1994
  • The experimental study is carried out to identify the combustion generated noise mechanism in free turbulent jet diffusion flames. Axial mean fluctuating velocities in cold and reacting flow fields were measured using hot-wire anemometer and LDv.The overall sound pressure level and their spectral distribution in far field with and without combustion were also measured in an anechoic chamber. The axial mean velocity is 10-25% faster and turbulent intensities are about 10 to 15% smaller near active reacting zone than those in nonreacting flow fields. And sound pressure level is about 10-20% higher in reacting flow fields. It is also shown that the spectra of the combustion noise has lower frequency characteristics over a broadband spectrum. These results indicate that the combustion noise characteristics in jet diffusion flames are dominated by energy containing large scale eddies and the combusting flow field itself. Scaling laws correlating the gas velocity and heat of combustion show that the acoustic power of the combustion noise is linearly proportional to the 3.8th power of the mean axial velocity rather than 8th power in nonreacting flow fields, and the SPL increases linearly with logarithmic 1/2th power of the heat of combustion.

The Effect of Residence Time on the Generation of Silica Nanoparticles in a Turbulent Diffusion Flame (난류 확산화염에서 체류시간이 실리카 나노입자의 생성에 미치는 영향)

  • Kwak, In-Jae;Bae, Soo-Ho;Shin, Hyun-Dong
    • 한국연소학회:학술대회논문집
    • /
    • 2006.10a
    • /
    • pp.196-201
    • /
    • 2006
  • Silica(SiO2) nanoparticles are used as additives in plastics and rubbers to improve mechanical, electrical, magnetic properties and optical material. Silica nanoparticles were synthesized by the gas phase thermal oxidation of several kinds of precursors in many types of reactor. Diffusion flame reactor has some advantages compared with other types of reactors. In this study, we investigated the generation of silica nanoparticles on the effect of residence time by tetraethylothosilicate(TEOS) in a turbulent diffusion flame reactor controlled by providing reactant flowrate and reactor geometry affect particle morphology, particle size and particle size distribution. To determine the flame residence time, flame length should be determined which was examined by ICCD image. Particle size, distribution and morphology were performed with TEM.

  • PDF

On the Effect of Presumed PDF and Intermittency on the Numerical Simulation of a Diffusion Flame

  • Riechelmann, Dirk;Fujimori, Toshiro
    • Journal of the Korean Society of Combustion
    • /
    • v.6 no.2
    • /
    • pp.23-28
    • /
    • 2001
  • In the present work, the effect of PDF selection and intermittency on the result of the numerical simulation are examined by the simulation of a turbulent methane-air jet diffusion flame. As to the PDFs, beta-function and clipped Gaussian are considered. Results for the pure mixing jet are compared with experimental results. Then, the turbulent flame is calculated for the same conditions and the results obtained for the several models are compared. It is found that the clipped Gaussian distribution coupled with consideration of intermittency recovers the experimental data very well. As to the reacting flow results, the main overall properties of the turbulent jet diffusion flame such as maximum flame temperature are less affected by the choice of the PDF. Flame height and NO emissions, on the contrary, appear to be significantly influenced.

  • PDF