• Title/Summary/Keyword: boundary characteristics

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Wake Characteristics of Vane-Type Vortex Generators in a Flat Plate Laminar Boundary Layer

  • Shim, HoJoon;Jo, Young-Hee;Chang, Kyoungsik;Kwon, Ki-Jung;Park, Seung-O
    • International Journal of Aeronautical and Space Sciences
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    • v.16 no.3
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    • pp.325-338
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    • 2015
  • Experimental and numerical investigations were conducted to identify the wake characteristics downstream of two vane-type vortex generators over laminar flat plate boundary layer. Experimental study was carried out by using the stereoscopic particle image velocimetry. To describe the flow field around the vortex generator in detail, numerical study was performed. We considered two different planform shapes of vortex generator: triangular and rectangular shape. The height of the generator was chosen to be about the boundary layer thickness at the position of its installation. Two different lengths of the generator were chosen: two and five times the height. Wake measurements were carried out at three angles of attack for each configuration. Wake characteristics for each case such as overall vortical structure, vorticity distribution, and location of vortex center with downstream distance were obtained from the PIV data. Wake characteristics, as expected, were found to vary strongly with the geometry and angle of attack so that no general tendency could be deduced. Causes of this irregular tendency were explained by using the results of the numerical simulation.

The Boundary Tones in Korean Intonational Phrases (한국어 억양구의 경계톤)

  • Han, Sun-Hee;Oh, Mi-Ra
    • Speech Sciences
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    • v.5 no.2
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    • pp.109-129
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    • 1999
  • A study of boundary tones, which are realized at the final syllable of an Intonational Phrase, is important in that sentential meaning is often differentiated solely by the use of different boundary tones in Korean. The purposes of this paper are three-fold: Firstly, it aims at finding out the different characteristics of boundary tones between designed corpus and natural speech. Secondly, it is to show that gender and dialectal differences are crucial factors in determining different realizations of boundary tones. Finally, this study is to provide a basis for better speech synthesis and speech recognition through the analysis of the morphemes where boundary tones are realized. This study has shown that nine different kinds of boundary tones are realized based on the contextual, gender and dialectal differences. In addition to the boundary tones suggested in Jun (1993), three more boundary toes are introduced: L-%,H-%,LHLH%.

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Influence of Flow Conditions on a Boundary Layer to the Near-Wake of a Flat Plat (평판 경계층 유동조건이 근접후류에 미치는 영향)

  • Kim, D.H.;Chang, J.W.
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1625-1630
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    • 2004
  • An experimental study was carried out to investigate influence of flow conditions on a boundary layer to the near-wake of a flat plate. The flow condition in the vicinity of trailing edge that is influenced by upstream condition history is an essential factor that determines the physical characteristics of a near-wake. Various tripping wires were used to change boundary layer flow condition of upstream at the freestream velocity of 6.0 m/sec. Measurements of the boundary layer and near-wake according to the change of upstream conditions were conducted by using both I-probe(55P14 for boundary layer) and X-probe(55P61 for wake). Normalized velocity profiles of the boundary layer were shown the flow types such as laminar boundary layer, transition, and turbulent boundary layer at 0.95C from the leading edge. The velocity and turbulence intensity profiles of the near-wake for the case of laminar boundary layer at the flat plate surface exhibited a defect and a double peak showing perfect symmetry, respectively.

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Grain boundary structure and electrical characteristics of alkaline metallic cation-diffused $(SrCa)TiO_3$ ceramics (알칼리 금속 이온의 입계확산에 따른 $(SrCa)TiO_3$ 소결체의 입계구조 및 전기적 특성)

  • Heo, Hyeon;Cho, Nam-Hui
    • Journal of the Korea Institute of Military Science and Technology
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    • v.2 no.1
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    • pp.183-193
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    • 1999
  • Semiconducting (Sr0.85Ca0.15)TiO3 ceramics were prepared by conventional powder synthesis techniques, and then alkaline metallic cations were diffused into the ceramic bodies. The threshold voltage of the ceramics increases with increasing diffusion time and the amount of diffused materials. The ceramics had boundary potential heights of 0.01 ~ 2.89 eV, while their boundary resistance ranged from 2.2 $M{\Omega}$ to 120.4 $M{\Omega}$. Such electrical characteristics of the boundaries were correlated with the boundary structure of the ceramics obtained by transmission electron microscopy.

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Flow Characteristics of Transitional Boundary Layers on a Flat Plate Under the Influence of Freestream Turbulent Intensity (자유유동 난류강도 변화에 따른 평판위 천이 경계층의 유동특성에 관한 실험적 연구)

  • Shin, Sung-Ho;Jeon, Woo-Pyung;Kang, Shin-Hyoung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.9
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    • pp.1335-1348
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    • 1998
  • Flow characteristics in transitional boundary layers on a flat plate were experimentally investigated under three different freestream conditions i. e. uniform flow with 0.1 % and 3.7% freestream turbulent intensity and cylinder-wake with 3.7% maximum turbulent intensity. Instantaneous streamwise velocities in laminar, transitional and turbulent boundary layers were measured by I-type hot-wire probe. For estimation of wall shear stresses on the flat plate, measured mean velocities near the wall were applied to the principle of Computational Preston Tube Method (CPM). Distributions of skin friction coefficients were reasonably predicted in all developed boundary layers. Intermittency profiles, which were estimated using Conditional Sampling Technique in transitional boundary layers, were also consistent with previously published data. It was predicted that the incoming turbulent intensity had more influence on transition onset point and transition process than freestream turbulent intensity existed just over the transition region. It was also confirmed that non-turbulent and turbulent profiles in transitional boundary layers could not be simply treated as Blasius and fully turbulent profiles.

Calculation of three-dimensional boundary layer near the plane of symmetry of an automobile configuration (자동차 중앙대칭단면 부근의 3차원경계층 계산)

  • 최장섭;최도형;박승오
    • Journal of the korean Society of Automotive Engineers
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    • v.10 no.2
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    • pp.61-69
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    • 1988
  • The finite-difference three-dimensional boundary layer procedure of Chang and Patel is modified and applied to solve the boundary layer development on the automobile surface. The inviscid pressure distribution needed to solve the boundary layer equations is obtained by using a low order panel method. The plane of symmetry boundary layer exhibits the strong streamline divergence up to the midbody and convergence thereafter. The streamline divergence in front of the windshield helps the boundary layer to overcome the sever adverse pressure gradient and avoid the separation. The relaxation of the pressure right after the top of the wind-shield, on the other hand, makes the overly thinned boundary layer to readjust and prompts the streamlines to converge into the symmetry plane before the external streamlines do. The three-dimensional characteristics are less apparent after the midbody and the boundary layer is similar to that of the two-dimensional flow. The results of the off-plane-of-symmetry boundary layer are also presented.

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The Plan Characteristics of Shared Housing through the Boundaries of Shared Space - A Focusing on the case of Urban Area in Domestic and Overseas - (공유경계를 통해 본 공유주거의 계획특성 - 국내외 도심 속 사례를 중심으로 -)

  • Kang, Su-Gyeong;Kim, Yong-Sung
    • Korean Institute of Interior Design Journal
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    • v.25 no.6
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    • pp.3-14
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    • 2016
  • According to Plato's ontology, we lead our lives by establishing a relationship with others in the society. However in rapidly changing era, our lives was gradually moving towards personal tendency. Even for the relationship with family, not with others. Thus, awareness about owning properties has changed due to the sociocultural factors and increase number of single-person households. So in this study, the considerations for single-person housing were perceived through preceding research, and the elements making spatial boundary of shared housing were drawn to make rational space sharing based on the boundary with others and of the living environment. With overall analysis based on the spatial boundary features of planned shared housing, the plan characteristics according to the spatial boundary of the current shared housing is to be drawn and analyzed. Third, The expressive and structural features of spatial boundary as above appear with mutual flexible connectivity, And the result shows that the modularity was the highest. Among them variable coupling modularity of shows how it is possible to combine efficiently and variously the private and public spaces with regularity of 'space of optimal unit'. This study drew plan characteristics from more detailed space border of shared housing. Therefore, The basic framework of the characteristics spin for the cases that newly emerge later on.

Numerical Analysis on the Flow Field and Heat Transfer Characteristics of Longitudinal Vortices in Turbulent Boundary Layer - On the Common Flow Up - (3차원 난류경계층 내에 존재하는 종방향 와동의 유동장 및 열전달 특성에 관한 수치해석(II) - Common Flow Up에 관하여 -)

  • Yang Jang-Sik
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.9
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    • pp.799-807
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    • 2005
  • The flow characteristics and the heat transfer rate on a surface by the interaction of a pair of vortices are studied numerically. To analyze the common flow up produced by vortex generators in a rectangular channel flow, the pseudo-compressibility viscous method is introduced into the Reynolds-averaged Navier-Stokes equation for 3-dimensional unsteady, incompressible viscous flows. To predict turbulence characteristics, a two-layer $k-\varepsilon$ turbulence model is used on the flat plate 3-dimensional turbulence boundary The computational results predict accurately Reynolds stress, turbulent kinetic energy and flow field generated by the vortex generators. The numerical results, such as thermal boundary layers, skin friction characteristics and heat transfers, are also reasonably close to the experimental data.

Investigation of Turbulence Characteristics of Defect Law Region over Flat plate (평판 위 흐름 Defect Law 영역의 난류 특성 연구)

  • Suh, Sung-Bu;Park, Il-Ryong;Jung, Kwang-Hyo;Lim, Jung-Gwan;Kim, Kwang-Soo;Kim, Jin
    • Journal of Ocean Engineering and Technology
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    • v.28 no.4
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    • pp.268-273
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    • 2014
  • To investigate the turbulence characteristics within the boundary layer over a flat plate, an experimental study was performed using a PIV technique in a circular water channel. For two water velocities, 0.92 and 1.99 m/s, the water velocity profiles were taken and analyzed to determine turbulent characteristics such as the Reynolds stress, Taylor micro-length scale, and Kolmogorov length scale within the defect law region of the boundary layer. These analysis methods may be applied to research on the friction drag reduction technology using micro-bubbles or an air sheet over the surface of a ship's hull, because the physical reason for the friction drag reduction could be found by understanding the variation of the turbulence characteristics and structures in the boundary layer.