• Title, Summary, Keyword: turbulence characteristics

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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
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    • v.18 no.9
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    • pp.2423-2430
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    • 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.

Generation of inflow turbulent boundary layer for LES computation

  • Kondo, K.;Tsuchiya, M.;Mochida, A.;Murakami, S.
    • Wind and Structures
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    • v.5 no.2_3_4
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    • pp.209-226
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    • 2002
  • When predicting unsteady flow and pressure fields around a structure in a turbulent boundary layer by Large Eddy Simulation (LES), velocity fluctuations of turbulence (inflow turbulence), which reproduce statistical characteristics of the turbulent boundary layer, must be given at the inflow boundary. However, research has just started on development of a method for generating inflow turbulence that satisfies the prescribed turbulence statistics, and many issues still remain to be resolved. In our previous study, we proposed a method for generating inflow turbulence and confirmed its applicability by LES of an isotropic turbulence. In this study, the generation method was applied to a turbulent boundary layer developed over a flat plate, and the reproducibility of turbulence statistics predicted by LES computation was examined. Statistical characteristics of a turbulent boundary layer developed over a flat plate were investigated by a wind tunnel test for modeling the cross-spectral density matrix for use as targets of inflow turbulence generation for LES computation. Furthermore, we investigated how the degree of correspondence of the cross-spectral density matrix of the generated inflow turbulence with the target cross-spectral density matrix estimated by the wind tunnel test influenced the LES results for the turbulent boundary layer. The results of this study confirmed that the reproduction of cross-spectra of the normal components of the inflow turbulence generation is very important in reproducing power spectra, spatial correlation and turbulence statistics of wind velocity in LES.

A Study on the Combustion Characteristics of Turbulent Diffusion Flame Stabilized by Bluff Body (보염기에 의해 안정되는 난류확산화염의 연소특성에 관한 연구)

  • An, J.G.;Song, K.K.
    • Journal of the Korean Society of Combustion
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    • v.3 no.1
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    • pp.71-78
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    • 1998
  • The flame stabilization and the combustion characteristics of diffusion flame formed in the wake of a cylindrical bluff body with fuel injection are studied. With the turbulence generator, the flame stability limits and ion currents were measured and analyzed. The results from this experimental study are summarized as follows. The region with highest average value of ion currents in the middle of flame is moved to the upstream side by the turbulent components of main stream. The flame mass with partially active reaction is moved fast for uniform flow and turbulence generator G3, but the flame mass with relatively slow reaction is moved slowly for turbulence generator G1. If the turbulence generator with strong turbulent component is installed, the turbulent time scale is increased with movement from main stream side to recirculation zone as well as the flame stability limits is deteriorated. Though the special dominant frequency is not appeared in the eddy which exists in flame, high frequency characteristics are appeared in uniform flow and turbulence generator G3, and low frequency characteristics are appeared in uniform flow, turbulence generator G3 and G1.

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Turbulence Characteristics of a Leakage Vortex in an Axial-Flow Fan (축류 팬 누설 와류의 난류 특성)

  • Myung, Hwan-Joo;Baek, Je Hyun;Rew, Ho-Seon;Lee, In-Seop
    • 유체기계공업학회:학술대회논문집
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    • pp.227-233
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    • 1999
  • Detailed Measurements were made to investigate the turbulence characteristics of a leakage vortex in an axial-flow fan using three-dimensional LDV. The turbulence in the leakage vortex has highly anisotropic characteristics with the radial value being the maximum. The turbulence intensity components in the vortex in the streamwise and tangential directions increase up to a certain downstrean position and then decrease. This increase is mainly due to the rapid decrease of the streamwise velocity of the vortex and partly due to the radial gradient of the streamwise velocity caused by a velocity deficit. As the vortex decays moving downstream, turbulence intensity also decrease gradually.

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Performance Evaluation of Two-Equation Turbulence Models for 3D Wing-Body Configuration

  • Kwak, Ein-Keun;Lee, Nam-Hun;Lee, Seung-Soo;Park, Sang-Il
    • International Journal of Aeronautical and Space Sciences
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    • v.13 no.3
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    • pp.307-316
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    • 2012
  • Numerical simulations of 3D aircraft configurations are performed in order to understand the effects of turbulence models on the prediction of aircraft's aerodynamic characteristics. An in-house CFD code that solves 3D RANS equations and two-equation turbulence model equations are used. The code applies Roe's approximated Riemann solver and an AF-ADI scheme. Van Leer's MUSCL extrapolation with van Albada's limiter is also adopted. Various versions of Menter's $k-{\omega}$ SST turbulence models as well as Coakley's $q-{\omega}$ model are incorporated into the CFD code. Menter's $k-{\omega}$ SST models include the standard model, the 2003 model, the model incorporating the vorticity source term, and the model containing controlled decay. Turbulent flows over a wing are simulated in order to validate the turbulence models contained in the CFD code. The results from these simulations are then compared with computational results from the $3^{rd}$ AIAA CFD Drag Prediction Workshop. Numerical simulations of the DLR-F6 wing-body and wing-body-nacelle-pylon configurations are conducted and compared with computational results of the $2^{nd}$ AIAA CFD Drag Prediction Workshop. Aerodynamic characteristics as well as flow features are scrutinized with respect to the turbulence models. The results obtained from each simulation incorporating Menter's $k-{\omega}$ SST turbulence model variations are compared with one another.

The Analysis of the the characteristics of Korean peninsula Aircraft Turbulence Index using KWRF (KWRF를 활용한 한반도 항공기 난류 지수 특성 분석)

  • Kim, Young-Chul
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.18 no.1
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    • pp.89-99
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    • 2010
  • The purpose of this study is analysis of Korean peninsula aircraft turbulence using the numerical weather prediction model, KWRF with the various turbulence index and pilot weather report data. Compared with the pilot weather report data and Calculated the turbulence index using the KWRF model result, many turbulence index show the similar horizontal distribution, except for the TUB2 and VWS. The analysis of vertical structure of turbulence, there are some difference each turbulence index respectively, but severe turbulence turn up in 15,000ft almost turbulence index. above 20,000ft height, intensity of turbulence vary each turbulence index. Through this turbulence study, It is founded on the research and development of the Korean peninsula aircraft turbulence

Dynamic Analysis of a Large Tilting Pad Journal Bearing Including the Effects of Temperature Rise and Turbulence (온도상승 및 난류효과를 고려한 대형 틸팅패드 저널베어링의 동특성 해석)

  • 하현천;김경웅
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.2
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    • pp.313-321
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    • 1995
  • The effects of the temperature rise and the turbulence are very important factors to predict the accurate performance of a large tilting pad journal bearing. In this study, the dynamic characteristics of a large tilting pad journal bearing are analyzed, taking into account the three dimensional variation of lubricant viscosity and turbulence. The effects of the temperature rise and the turbulence on the stiffness and damping coefficients are investigated in comparison with the results from the laminar or isothermal theory. The stiffness and damping coefficients increase due to the turbulence but decrease due to the temperature rise. The results show that the effects of both the temperature rise and turbulence must be considered simultaneously in order to predict the dynamic characteristics of a large tilting pad journal bearing more accurately.

A forensic study of the Lubbock-Reese downdraft of 2002

  • Holmes, J.D.;Hangan, H.M.;Schroeder, J.L.;Letchford, C.W.;Orwig, K.D.
    • Wind and Structures
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    • v.11 no.2
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    • pp.137-152
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    • 2008
  • This paper discusses engineering aspects of the rear-flank downdraft that was recorded near Lubbock, Texas on 4 June 2002, and produced a gust wind speed nearly equal to the design value (50-year return period) for the region. The general characteristics of the storm, and the decomposition of the time histories into deterministic 'running mean' and random turbulence components are discussed. The fluctuating wind speeds generated by the event can be represented as a dominant low-frequency 'running mean' with superimposed random turbulence of higher frequencies. Spectral and correlation characteristics of the residual turbulence are found to be similar to those of high-frequency turbulence in boundary-layer winds. However, the low-frequency components in the running-mean wind speeds are spatially homogeneous, in contrast to the low-frequency turbulence found in synoptic boundary-layer winds. With respect to transmission line design, this results in significantly higher 'span reduction factors'.

A Study on the Flow characteristics in dividing Rectangular ducts (사각분기 덕트내의 유동특성에 관한 연구)

  • 이행남;박길문;이덕구
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • pp.270-275
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    • 2001
  • The characteristics of flow in dividing regions are precise, therefore their classification is very important not only in industry but also in hydrodynamics. By now, many studies of flow in dividing regions have been peformed, but flow characteristics that use visualization In dividing regions have not been studied. The present study of the PIV and the CFD exhibit average velocity distributions, kinetic energy distributions and total pressure distributions etc of the total flow field due to the development of the accurate visualization optical laser and of optical equipment. Also, PIV is accurate with the flows characteristics of the dividing region as continuous analysis is done using input equipment. The study analyzes velocity vector field, turbulence kinetic energy, turbulence viscosity of dividing regions with flow for visualization of the PIV and the CFD measurement in a dividing rectangular ducts.

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Wind spectral characteristics on strength design of floating offshore wind turbines

  • Udoh, Ikpoto E.;Zou, Jun
    • Ocean Systems Engineering
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    • v.8 no.3
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    • pp.281-312
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    • 2018
  • Characteristics of a turbulence wind model control the magnitude and frequency distribution of wind loading on floating offshore wind turbines (FOWTs), and an in-depth understanding of how wind spectral characteristics affect the responses, and ultimately the design cost of system components, is in shortage in the offshore wind industry. Wind spectrum models as well as turbulence intensity curves recommended by the International Electrotechnical Commission (IEC) have characteristics derived from land-based sites, and have been widely adopted in offshore wind projects (in the absence of site-specific offshore data) without sufficient assessment of design implications. In this paper, effects of wind spectra and turbulence intensities on the strength or extreme responses of a 5 MW floating offshore wind turbine are investigated. The impact of different wind spectral parameters on the extreme blade loads, nacelle accelerations, towertop motions, towerbase loads, platform motions and accelerations, and mooring line tensions are presented and discussed. Results highlight the need to consider the appropriateness of a wind spectral model implemented in the strength design of FOWT structures.