• Title/Summary/Keyword: 큰에디모사

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Large Eddy Simulation of Flow and Heat Transfer in a Rotating Ribbed Channel (요철이 설치된 회전하는 채널 내부의 유동 및 열전달의 큰에디모사)

  • Ahn, Joon;Choi, Hae-Cheon;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.193-198
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    • 2003
  • A gas turbine blade has an internal cooling passage equipped with ribs, which can be modeled as a ribbed channel. We have studied a flow inside a ribbed channel using large eddy simulaton (LES) with a dynamic subgrid-scale model. The simulation results are compared with the experimental ones. The turbulence intensity and local heat transfer near the rib have not been well captured by the conventional Reynolds averaged Navier-Stokes simulation (RANS). However, these variables obtained by the present LES agree well with those from experiments. From the instantaneous velocity and temperature fields, we explain the mechanisms responsible for the local peaks in the heat transfer distribution along the channel wall. We have also investigated the effect of rotation on the flow and heat transfer in the ribbed channel.

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Large Eddy Simulation of Flow and Heat Transfer in a Channel Roughened by Square or Semicircle Ribs (사각 또는 반원 형상의 요철이 설치된 채널 내부의 유동 및 열전달의 큰에디모사)

  • Ahn, Joon;Choi, Hae-Cheon;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1436-1441
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    • 2004
  • The internal cooling passage of a gas turbine blade can be modeled as a ribbed channel. Most studies have considered square ribs. However, the ribs can be rounded due to improper manufacturing or wear during the operation. Hence, we have studied two different rib geometries in this study, i.e. square and semicircle ribs. We have performed large eddy simulations (LES) and experiments to validate the results from the simulations. LES predicts the detailed flow and thermal features, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms for the local heat transfer distribution between ribs. For both the geometries, heat transfer is enhanced by the entrainment of the cold fluid by the vortical motions and impingement of the entrained cold fluid on the ribs.

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LES for unsteady flow past n cavity (공동을 지나는 비정상 유동에 대한 LES 해석)

  • Lim Jongsoo;shin Dongshin
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.791-794
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    • 2002
  • Cavity is inevitably included in automobile vehicle configuration. The complex unsteady flow and sound waves generated by the cavity are very important issues because of the involved fluid dynamics and the practical importance in the field of aerodynamics. The LES method used is a conventional one with Smagorinsky eddy-viscosity model and the computational grid is small enough to be handled by workstation-level computers. LES can successfully simulate of cavity noise analysis.

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COARSE GRID LARGE-EDDY SIMULATION OF FLOW OVER A HEAVY VEHICLE (화물차 주위 유동의 성긴 격자 큰에디모사)

  • Lee, S.;Kim, M.;You, D.;Kim, J.J.;Lee, S.J.
    • Journal of computational fluids engineering
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    • v.21 no.1
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    • pp.30-35
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    • 2016
  • In order to investigate effects of grid resolution on large-eddy simulation of flow over a heavy vehicle, large-eddy simulations over the vehicle with coarse grid and fine grid are conducted. In addition, comparison of drag coefficients with the experimental data obtained by a wind tunnel experiment is conducted. Both of the drag coefficients of coarse grid and fine grid large-eddy simulation show good agreement with the experimental data. Flow fields obtained by the coarse and the fine grid large-eddy simulation are compared in the vehicle frontal-face region, the vehicle rear wheel region, and the vehicle base region. Coarse grid large-eddy simulation shows good agreement with the fine grid large-eddy simulation in the vehicle front face region and the vehicle rear wheel region, since the flow over the present vehicle is dominated by flow separation which is geometrically pre-determined, not by the skin friction which is known to be sensitive to grid resolution.

Effects of Dimple Depth and Reynolds Number on the Flow and Heat Transfer in a Dimpled Channel (딤플이 설치된 채널에서 레이놀즈 수 및 딤플 깊이에 따른 유동 및 열전달 특성)

  • Ahn, Joon;Lee, Young-Ok;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.3253-3258
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    • 2007
  • A large eddy simulation (LES) has been conducted for the flow and heat transfer in a dimpled channel. Two dimple depths of 0.2 and 0.3 times of the dimple print diameter (= D) have been compared at the bulk Reynolds number of 20,000. Three Reynolds numbers of 5,000, 10,000 and 20,000 have been studied, while the dimple depth is kept as 0.2 D. With the deeper dimple, the flow reattachment occurs father downstream inside the dimple, so that the heat transfer is not as effectively enhanced as the case with shallow ones. At the low Reynolds number of 5,000, the Nusselt number ratio is as high as those for the higher Reynolds number, although the value of heat transfer coefficient decreases because of the weak shear layer vortices.

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Suppression of Turbulence in a Circular Jet Using a Single Frequency Excitation (단일 주파수 가진을 이용한 원형 제트의 난류 억제)

  • Park Jeongyoung;Choi Haecheon
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.241-244
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    • 2002
  • Large eddy simulation of a circular jet at the Reynolds number of 10000 is performed to investigate turbulence suppression effect with single frequency excitation at the non-dimensional frequency of 0.017. Instantaneous flow fields show that, with excitation, naturally occurring energetic vortices are suppressed through earlier saturation and breakdown of the shear layer vortices into fine grained turbulence. Due to the excitation, the Reynolds stresses are larger for the excited case near the jet and turbulence suppression begins afterward. The Reynolds normal stresses show largest suppression in the shear layer near the jet and in the centerline further downstream, while the Reynolds shear stress shows largest suppression in the shear layer at all the downstream locations.

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NUMERICAL INVESTIGATION OF TURBULENT FLOW FROM AN ANNULAR JET (환형제트 난류유동에 대한 수치해석 연구)

  • Kim, Jungwoo
    • Journal of computational fluids engineering
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    • v.18 no.4
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    • pp.47-52
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    • 2013
  • In the present study, the turbulent flow from an annular jet is investigated by using large eddy simulation. Particularly, the effect of the ratio of the inner and outer diameters is one of the main interests of this study. The instantaneous fields presented in this paper showed that behind the jet exit the backflow region, as well known in literatures, exists, and its detailed behavior depends on the ratio of the inner and outer diameters ($D_1/D_2$). The dependence on $D_1/D_2$ is attributed to the different shear layer development according to $D_1/D_2$. At small $D_1/D_2$, the development of the outer shear layer is similar to that from the circular jet. However, with increasing $D_1/D_2$, the interaction between the outer and inner shear layers becomes strong, resulting in fast transition to turbulence.

Numerical Study on the Drag of a Car Model under Road Condition (주행조건에서의 자동차 모델 항력에 대한 수치해석적 연구)

  • Kim, Beom-Jun;Kang, Sung-Woo;Choi, Hyoung-gwon;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.8
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    • pp.1182-1190
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    • 2003
  • A parallelized FEM code based on domain decomposition method has been recently developed for large-scale computational fluid dynamics. A 4-step splitting finite element algorithm is adopted for unsteady flow computation of the incompressible Navier-Stokes equation, and Smagorinsky LES model is chosen for turbulent flow computation. Both METIS and MPI Libraries are used for domain partitioning and data communication between processors, respectively. Tiburon model of Hyundai Motor Company is chosen as the computational model at Re=7.5 $\times$ 10$^{5}$ , which is based on the car height. The calculation is carried out under both the wind tunnel condition and the road condition using IBM SP parallel architecture at KISTI Super Computing Center. Compared with the existing experimental data, both the velocity and pressure fields are predicted reasonably well and the drag coefficient is in good agreement. Furthermore, it is confirmed that the drag under the road condition is smaller than that under the wind-tunnel condition.

LARGE EDDY SIMULATION OF THE FLOW AROUND A SPHERE WITH UNSTRUCTURED MESH (비정렬 격자를 이용한 구 주위의 큰에디 모사)

  • Lee, K.S.;Baek, J.H.
    • 한국전산유체공학회:학술대회논문집
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    • 2007.04a
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    • pp.41-44
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    • 2007
  • A large eddy simulation method with unstructured mesh is presented. Two explicit filtering procedures are adopted for reducing the aliasing error of the nonlinear convective term and measuring the level of subgrid scale velocity fluctuation, respectively. The developed subgrid scale model is basically an eddy viscosity model which depends on both local velocity fluctuation level and local grid scale. As a validation problem, the flows around a sphere of several Reynolds numbers are simulated and some characteristic quantities are compared to experimental data and numerical results in the literature.

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