• Title/Summary/Keyword: Chimera 격자기법

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A Grid Adaptation Method Using the Chimera and Patched Grid Systems (중첩격자계와 접합격자계를 이용한 적응격자 기법)

  • Kim, De-Hee;Kwon, Jang-Hyuk
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.10
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    • pp.17-25
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    • 2005
  • A grid adaptation method within systems of chimera and patched grids is presented. Problem domains are divided into near-body and off-body fields. Near-body field is filled with curvilinear body-fitted grids that extend only a short distance from body surfaces and connected to other grid systems via chimera domain connectivity method. Off-body field is filled with patched uniform cartesian grids of varying levels of refinement. This method gives flexibility in grid generation and efficient adaptation capability. Several numerical experiments including 2D store separation were performed to show the performance of the proposed adaptation method.

Validation of Chimera Grid Method Applied to UMSAPv With Prediction of Carriage Load (장착하중 예측을 통한 UMSAPv에 적용된 중첩 격자 기법 검증)

  • Kang, SeonWook;Ahn, Kyehyun;Lee, Seungsoo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.50 no.10
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    • pp.669-676
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    • 2022
  • In this paper, the carriage load analyses of stores installed on aircraft are conducted to validate the chimera grid method applied to an unstructured CFD solver, UMSAPv. First, the chimera grid method of UMSAPv is verified for the well-known Eglin Wing/Pylon/Finned store problem. Next, an angle of attack sweep of F/A-18C clean configuration is conducted at a subsonic speed. The computed results are compared with the results of the previous study using MSAPv, a structured CFD solver, to show the validity of Umsapv. Finally, the carriage of F/A-18C JDAM is carried out with a chimera grid as well as a single block grid. The computed results are compared with other computational, experimental and the flight tests.

Analysis of the flow field around an automobile with Chimera grid technique (Chimera 격자기법을 이용한 자동차 주위의 유동장 해석)

  • An, Min-Gi;Park, Won-Gyu
    • Journal of computational fluids engineering
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    • v.3 no.2
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    • pp.39-51
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    • 1998
  • This paper describes the analysis of flow field around an automobile. The governing equations of the 3-D unsteady incompressible Navier-Stokes equations are solved by the iterative time marching scheme. The Chimera grid technique has been applied to efficiently simulate the flow around the side-view mirror. To validate the capability of simulating the flow around a ground vehicle, the flows around the Ahmed body with 12.5$^{\circ}$ and 30$^{\circ}$ of slant angles are simulated and good agreements with experiment and other numerical results are achieved. To validate Chimera grid technique, the flow field around a cylinder was also calculated. The computed results are also well agreed with other numerical results and experiment. After code validations, the flow phenomena around the ground vehicle are evidently shown. The flow around the side-view mirror is also well simulated using the Chimera grid technique.

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A Study of Parallel Implementations of the Chimera Method using Unsteady Euler Equations (비정상 Euler 방정식을 이용한 Chimera 기법의 병렬처리에 관한 연구)

  • Cho K. W.;Kwon J. H.;Lee S.S
    • Journal of computational fluids engineering
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    • v.4 no.3
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    • pp.52-62
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    • 1999
  • The development of a parallelized aerodynamic simulation process involving moving bodies is presented. The implementation of this process is demonstrated using a fully systemized Chimera methodology for steady and unsteady problems. This methodology consists of a Chimera hole-cutting, a new cut-paste algorithm for optimal mesh interface generation and a two-step search method for donor cell identification. It is fully automated and requires minimal user input. All procedures of the Chimera technique are parallelized on the Cray T3E using the MPI library. Two and three-dimensional examples are chosen to demonstrate the effectiveness and parallel performance of this procedure.

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Verification of Hovering Rotor Analysis Code Using Overlapped Grid (중첩격자를 이용한 제자리비행 로터 해석 코드의 수치특성)

  • Kim, Jee-Woong;Park, Soo-Hyung;Yu, Yung-Hoon;Kim, Eu-Gene;Kwon, Jang-Hyuk
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.8
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    • pp.719-727
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    • 2008
  • A 3-D compressible Navier-Stokes solver using overlapped grids is developed to predict a flow-field around a hovering rotor. The flow solver is verified by a parametric study with the grid spacing of wake grid, spatial accuracy and turbulence model. Computations are performed with different Chimera grid systems. Computational results are compared with the experimental data of Caradonna et al. for both blade loading and the tip vortex behavior. Numerical results show good agreements with experiments for the distribution of surface pressure and tip vortex behavior. Pressure distributions over the blade have marginal differences for different numerical methods, whereas large discrepancies are seen in the prediction of the wake behavior. Results unexpectedly show that the vortex strength from an automated cut-paste Chimera grid is weaker than that from the conventional Chimera grid.

An Unstructured 3-D Chimera Technique for Overlapped Bodies inRelative Motion (3차원 비정렬 중첩격자계를 이용한 서로 겹쳐진 물체들 간의 상대운동 해석기법에 관한 연구)

  • 안상준;권오준;정문승
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.8
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    • pp.1-7
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    • 2006
  • In the present study, A 3-D chimera technique for overlapped bodies in relative motion is studied using unstructured meshes. If all node points of a mesh element at solid boundary are in another body, this element is excluded from computational domain. For computation of unsteady flow, non-active cells have proper variables using interpolation and extrapolation. These variables are used in next time step. The motion of a launching trajectory ejected from a wing and the motion of deploying fins of a trajectory which have not been simulated are computed to conform practicality of this technique.

Numerical analysis of flow field around an automobile with variation of yaw angles (측풍의 편향각 변화에 따른 자동차 주위의 유동해석)

  • Kang D. M.;Jung Y. R.;Park W. G.;Ha S. D.
    • Journal of computational fluids engineering
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    • v.4 no.3
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    • pp.1-11
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    • 1999
  • This paper describes the flow field analysis of an automobile with crosswind effects of 15°, 30° 45° and 60° of yaw angles. The governing equations of the 3-D incompressible Navier-Stokes equations are solved by the iterative time marching scheme. The Chimera grid technique has been applied to efficiently simulate the flow around the side-view mirror. The computated surface pressure coefficients have been compared with experimental results and a good agreement has been achieved. The A- and C-pillar vortex and other flow phenomena around the ground vehicle are evidently shown. The variation of aerodynamic coefficients of drag, lift, side force and moments with respect to yaw angle is systematically studied.

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APPLICATION OF MOVING LEAST SQUARE METHOD IN CHIMERA GRID METHOD (중첩격자에 대한 이동최소자승법 적용 연구)

  • Lee, K.;Lee, S.
    • 한국전산유체공학회:학술대회논문집
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    • 2007.04a
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    • pp.17-22
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    • 2007
  • Chimera grid Method is widely used in Computational Fluid Dynamics due to its simplicity in constructing grid system over complex bodies. Especially, Chimera grid method is suitable for unsteady flow computations with bodies in relative motions. However, interpolation procedure for ensuring continuity of solution over overlapped region fails when so-call orphan cells are present. We have adopted MLS(Moving Least Squares) method to replace commonly used linear interpolations in order to alleviate the difficulty associated with orphan cells. MSL is one of interpolation methods used in mesh-less methods. A number of examples with MLS are presented to show the validity and the accuracy of the method.

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Numerical Flow Simulations Around High Speed Train Using CHIMERA Grid Technique (CHIMERA 격자기법을 이용한 고속전철 주위의 전산유동해석)

  • Choi S. W.;Kim I. S.
    • Journal of computational fluids engineering
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    • v.1 no.1
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    • pp.81-87
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    • 1996
  • The aerodynamic charateristics of high speed train can be improved by well-designing of its fore-body shape. In this paper, as a way of the design a fore-body shape which has optimal aerodynamic charasteristics, 9 models of fore-body shapes are proposed and the change of aerodynamic charateristics is studied through calculations of flow field around high speed train for each fore-body shape. The flow field around high speed trains are calculated using Thin-Layer Navier-Stokes equation and Chimera grid technique. The application of Chimera grid technique to these flow calculations over high speed train which has ground plane under the train makes grid generation easily. As a computaional algorithm, Pulliam and Chaussee's Diagonal algorithm, the modified form of the Beam and Warming's AF scheme which operates on block-tridiagonal matrices, is selected to reduce computaional time. Introducing hole points flag concept to this Diagonal algorithm. a algorithm for Chimera grid is generated. The variational trends of aerodynamic characteristics are studied from the results of flow calculations around high speed trains for 9 fore-body shapes.

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APPLICATION OF MOVING LEAST SQUARE METHOD IN CHIMERA GRID METHOD (중첩격자에 대한 이동최소자승법 적용 연구)

  • Lee, K.;Lee, S.;Cho, J.Y.
    • Journal of computational fluids engineering
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    • v.13 no.1
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    • pp.49-56
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    • 2008
  • Chimera grid methods have been widely used in Computational Fluid Dynamics due to its simplicity in constructing grid systems over complex bodies, and suitability for unsteady flow computations with bodies in relative motion. However, the interpolation procedure for ensuring the continuity of the solution over overlapped regions fails when the so-called orphan cells are present. We have adopted the MLS(Moving Least Squares) method to replace commonly used linear interpolations in order to alleviate the difficulty associated with the orphan cells. MLS is one of the interpolation methods used in mesh-less methods. A number of examples with MLS are presented to show the validity and the accuracy of the method.