• Title, Summary, Keyword: Turbulence Flow

Search Result 2,117, Processing Time 0.041 seconds

Large eddy simulation of a square cylinder flow: Modelling of inflow turbulence

  • Tutar, M.;Celik, I.
    • Wind and Structures
    • /
    • v.10 no.6
    • /
    • pp.511-532
    • /
    • 2007
  • The present study aims to generate turbulent inflow data to more accurately represent the turbulent flow around a square cylinder when the inflow turbulence level is significant. The modified random flow generation (RFG) technique in conjunction with a previously developed LES code is successfully adopted into a finite element based fluid flow solver to generate the required inflow turbulence boundary conditions for the three-dimensional (3-D) LES computations of transitional turbulent flow around a square cylinder at Reynolds number of 22,000. The near wall region is modelled without using wall approximate conditions and a wall damping coefficient is introduced into the calculation of sub-grid length scale in the boundary layer of the cylinder wall. The numerical results obtained from simulations are compared with each other and with the experimental data for different inflow turbulence boundary conditions in order to discuss the issues such as the synthetic inflow turbulence effects on the 3-D transitional flow behaviour in the near wake and the free shear layer, the basic mechanism by which stream turbulence interacts with the mean flow over the cylinder body and the prediction of integral flow parameters. The comparison among the LES results with and without inflow turbulence and the experimental data emphasizes that the turbulent inflow data generated by the present RFG technique for the LES computation can be a viable approach in accurately predicting the effects of inflow turbulence on the near wake turbulent flow characteristics around a bluff body.

A Study on Turbulence Flow Characteristics at the Spark Plug Location in S.I. Engine (가솔린기관의 점화플러그 위치에서 난류유동 특성에 관한 연구)

  • 정연종;조규상;김원배
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.18 no.9
    • /
    • pp.2423-2430
    • /
    • 1994
  • Several factors of the efficient combustion process are shape of combustion chamber, position of spark plug, turbulence flow and so on. the shape of combustion chamber and position of spark plug are constrained to geometrically, and then it could not make a change the shape easily. But the turlence flow in combustion chamber have a great influence on combustion phenomena, and which is much easier to control relatively. And since characteristics of turbulence flow would be very important to the stability of combustion and performances, This study is also essential to future engine-low emission and lean burn engine. This paper shows that the visualization of the turbulence flow of single cylinder engine by using 2way, $45^{\circ}$ inclined and 2 channel hot wire probe through the park plug hole. We also study the characteristics of turbulence flow by means of ensemble averaged mean velocity, turvulence intensity and integral length scale.

The Influences of Factors on Turbulence Intensity in Combustion Chamber (연소실내의 난류강도에 미치는 각종 인자의 영향)

  • 한성빈;이상준;이종태;이성열
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.18 no.3
    • /
    • pp.793-804
    • /
    • 1994
  • Turbulence intensity caused by piston movement was almost as same tendency as the piston speed. The turbulence intensity was increased from 0.39m/s to 0.79m/s when mean piston speed increased from 2.33m/s to 4.67m/s. In this case the maximum turbulence intensity caused by piston speed was decreased about 82 percent near the top dead center at the end of compression stroke. The maximum turbulence intensity was created from 12m/s to 22m/s when inlet flow velocity was increased from 22m/s to 45m/s. Also turbulence intensity caused by inlet flow velocity was linearly increased from 0.97m/s at top dead center at the end of compression stroke. The ratio of turbulence intensity and mean inlet flow velocity was about 3 percent for inlet flow velocity.

Effects of Combustor-Level High Free-Stream Turbulence on Blade-Surface Heat/Mass Transfer in the Three-Dimensional Flow Region near the Endwall of a High-Turning Turbine Rotor Cascade

  • Lee Sang Woo;Kwon Hyun Goo;Park Byung-Kyu
    • Journal of Mechanical Science and Technology
    • /
    • v.19 no.6
    • /
    • pp.1347-1357
    • /
    • 2005
  • Effects of combustor-level high free-stream turbulence on the blade-surface heat/mass transfer have been investigated in the three-dimensional flow region near the endwall within a high-turning turbine rotor cascade passage. Free-stream turbulence intensity and integral length scale in the high turbulence case are 14.7 percents and 80 mm, respectively. The result shows that there is no considerable discrepancy in the blade heat/mass transfer near the endwall between the low and high turbulence cases. As departing from the endwall, however, the deviation between the two cases becomes larger, particularly in the region where flow separation and re-attachment occur. Under the high turbulence, flow disturbances such as boundary-layer separation and re-attachment seem to be suppressed, which makes the blade heat/mass transfer more uniform. Moreover, there are some evidences that endwall vortices tend to be weakened under the high turbulence.

Assessment of Turbulence Models for Engine Intake and Compression Flow Analysis (엔진 흡입.압축과정의 유동해석을 위한 난류모델의 평가)

  • Park, Kweon-Ha;Kim, Jae-Gon
    • Journal of the Korean Society of Marine Engineering
    • /
    • v.32 no.8
    • /
    • pp.1129-1140
    • /
    • 2008
  • Many turbulence models have been developed in order to analyze the flow characteristics in an engine cylinder. Watkins introduced k-${\varepsilon}$ turbulence model for in-cylinder flow, and Reynolds modified turbulence dissipation rate by applying rapid transformation theory, Wu suggested k-${\varepsilon}-{\tau}$ turbulence model in which length scale and time scale are separated to introduce turbulence time scale, and Orszag proposed k-${\varepsilon}$ RNG model. This study applied the models to in-cylinder flow induced by intake valve and piston moving. All models showed similar flow fields during early stage of intake stroke. At the end of compression stroke, ${\kappa}-{\varepsilon}$ Watkins, ${\kappa}-{\varepsilon}$ Reynolds and ${\kappa}-{\varepsilon}$ RNG predicted well second and third vortex, especially ${\kappa}-{\varepsilon}$ RNG produced new forth vortex near central axis at the lower part of cylinder which was not predicted by the other models.

Effects of Combustor-Level High Inlet Turbulence on the Endwall Flow and Heat/Mass Transfer of a High-Turning Turbine Rotor Cascade

  • Lee, Sang-Woo;Jun, Sang-Bae;Park, Byung-Kyu;Lee, Joon-Sik
    • Journal of Mechanical Science and Technology
    • /
    • v.18 no.8
    • /
    • pp.1435-1450
    • /
    • 2004
  • Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The end wall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the end wall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the end wall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. In this study, the end wall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.

Performance Assessment of Turbulence Models for the Prediction of Tip Leakage Flow in an Axial-flow Turbomachinery (축류형 유체 기계에서 팁 누설 유동 해석을 위한 난류 모델 성능 비교)

  • Lee, Gong-Hee;Baek, Je-Hyun
    • Proceedings of the KSME Conference
    • /
    • /
    • pp.2162-2167
    • /
    • 2003
  • It is well-known that high anisotropic characteristic of turbulent flow field is dominant inside tip leakage vortex. This anisotropic nature of turbulence invalidates the use of the conventional isotropic eddy viscosity turbulence model based on the Boussinesq assumption. In this study, to check whether an anisotropic turbulence model is superior to the isotropic ones or not, the results obtained from steady-state Reynolds averaged Navier-Stokes simulations based on the RNG ${\kappa}-{\varepsilon}$ and the Reynolds stress model in two test cases, such as a linear compressor cascade and a forward-swept axial-flow fan, are compared with experimental data. Through the comparative study of turbulence models, it is clearly shown that the Reynolds stress model, which can express the production term and body-force term induced by system rotation without any modeling, should be used to predict the complex tip leakage flow, including the locus of tip leakage vortex center, quantitatively.

  • PDF

Evaluation of the Anisotropic k - ${\epsilon}$ Turbulence Model by the Numerical Analysis of Axisymmetric Swirling Turbulent Flow (축대칭 선회난류의 수치해석에 의한 비등방 k - ${\epsilon}$ 난류모델의 評價)

  • Lee, Yeon-Won
    • Journal of the Korean Society of Marine Engineering
    • /
    • v.20 no.5
    • /
    • pp.39-44
    • /
    • 1996
  • To overcome weak poinks of the standard k-${\varepsilon}$ turbulence model when applied to complex turbulent flows, various modified models were proposed. But their effects are confined to special flow fields. They have still some problems. Recently, an anisotropic k-${\varepsilon}$ turbulence model was also proposed to solve the drawback of the standard k-${\varepsilon}$ turbulence model. This study is concentrated on the evaluation of the anisotropic k-${\varepsilon}$ turbulence model by the analysis of axisymmetric swirling turbulent flow. Results show that the anisotropic k-${\varepsilon}$ turbulence model has scarecely the fundamentally physical mechanism of predicting the swirling structure of flow.

  • PDF

The Numerical Analysis on In-cylinder Flow Fields of an Axisymmetric Engine Using $K-{\varepsilon}-{\tau}$ Turbulence Model ($K-{\varepsilon}-{\tau}$ 난류모델을 이용한 축대칭 엔진 실린더내 유동장의 수치해석)

  • 최재성
    • Journal of the Korean Society of Marine Engineering
    • /
    • v.23 no.5
    • /
    • pp.711-718
    • /
    • 1999
  • Current turbulence models including modified $K-{\varepsilon}-{\tau}$ turbulence model do not predict compression effect on turbulence accurately in an internal combustion engine. The $K-{\varepsilon}-{\tau}$ turbulence model was suggested to improve the predictability of compression effect by We et al. In this paper a numeri-cal study was performed to clarify the applicability of the $K-{\varepsilon}-{\tau}$ turbulenc model to the calculation of the in-cylinder flow of an axisymmetric engine. THe results using $K-{\varepsilon}-{\tau}$ turbulence model are compared to those from the modified $K-{\varepsilon}-{\tau}$ turbulence model and experimental data. The mean veloc-ity and rms velocity profiles using $K-{\varepsilon}-{\tau}$ turbulence model showed a better agreement with an experimental data than those of modifid $K-{\varepsilon}-e$ turbulence model.

  • PDF

A Study on the Turbulence Enhancement of Jet Flow by the Ultrasonic Forcing in a Coaxial Circular Pipe (동심원관내에서 초음파가진에 의한 제트유동의 난류증진에 관한 연구)

  • Ju, E.S.;Lee, Y.H.;Song, M.G.;Lee, S.B.;Son, S.W.
    • Journal of the Korea Society For Power System Engineering
    • /
    • v.5 no.3
    • /
    • pp.31-37
    • /
    • 2001
  • A study to obtain the enhancement of turbulence at low Reynolds number is carried out by adding ultrasonic force into the jet flow field of a coaxial circular pipe which can afford the sufficient data of flow characteristics with the shear flow and turbulence flow in spite of its simple shape. A coaxial circular flow field is made vertically in a large and transparent acryl tank. The time mean velocity vector, distribution, kinetic energy and turbulence intensity formed in the complex flow field of turbulence enhancement are investigated, observed and discussed at Reynolds number of 2,000, 3,000 and 5,000 by using PIV measurement, in results, the validity of ultrasonic to obtain the enhancement of turbulence is certified.

  • PDF