• 한국전산유체공학회지
• /
• 제18권3호
• /
• pp.79-86
• /
• 2013

Preconditioned compressible Navier-Stokes equations are solved for almost incompressible flows. Unstructured meshes are utilized for spatial discretization of complex flow domain. Effectiveness of the current preconditioning algorithm, with respect to various Reynolds numbers and Mach numbers, is demonstrated by the solution of canonical problems for incompressible flows, e.g. driven cavity flows.

• International Journal of Automotive Technology
• /
• 제7권2호
• /
• pp.139-143
• /
• 2006

As an automobile tends to be high grade, the needs for more luxurious interior and comfortable HVAC system are emerged. The defrosting ability is another major factor of the performances of HVAC system. The present work is to simulate the flow and the temperature field of cabin interior during the defrost mode. The three-dimensional incompressible Navier-Stokes equations and energy equation were solved on the multi blocked grid system by the iterative time marching method and AF scheme, respectively. The present computations were validated by the comparison of the temperature field of a driven cavity and velocity field of 1/5 model scale of an automobile. Generally good agreements were obtained. By the present computation, the complicated features of flow and temperature within the automotive cabin interior could be well understood.

• 한국전산유체공학회지
• /
• 제12권4호
• /
• pp.38-43
• /
• 2007

Owing to the rapid progress in manufacturing technology of microscale devices, there are active research works in developing microscale propulsion systems. In this study, gas flows in nozzles with size of milli and sub-millimeter are investigated by using a CFD code based on the Navier-Stokes equations. The prediction results were compared with theoretical results of quasi-one-dimensional nozzle flow and experiment data. In general, theoretical values agree very well with the CFD results. However, theoretical values begin to deviate from the CFD and experimental data for relatively small Reynolds numbers and the nozzle shape with rectangular cross section. The primary reason for this discrepancy is due to the existence of the thick boundary layer at the wall in low Reynolds flows.

• 한국전산유체공학회지
• /
• 제1권1호
• /
• pp.71-80
• /
• 1996

An iterative time marching procedure for solving incompressible turbulent flow has been applied to the flows around a high speed train including cross-wind effects. This procedure solves three-dimensional unsteady incompressible Reynolds-averaged Navier-Stokes equations on a non-orthogonal curvilinear coordinate system using first-order accurate schemes for the time derivatives and third/second-order accurate schemes for the spatial derivatives. Turbulent flows have been modeled by Baldwin-Lomax turbulent model. To validate present procedure, the flow around a high speed train at zero yaw angle was simulated and compared with experimental data. Generally good agreement with experiments was achieved. The flow fields around the high speed train at 9.2°, 16.7°, and 45° of yaw angle were also simulated.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2011년도 제37회 추계학술대회논문집
• /
• pp.263-267
• /
• 2011

본 연구는 에틸렌-공기 혼합물로 채워져 있는 굽은 관에서의 충격파와 화염의 상호 작용, 화염 가속, 연소폭발천이 현상을 수치적으로 살펴보았다. 여기서 사용되는 모델은 지배방정식으로 Navier-Stokes 방정식과 경계조건 처리 방법으로 ghost fluid 기법을 사용하였다. 굽은 관에서 여러 충격파 강도를 이용한 모델링을 통하여 화염과 강한 충격파의 충돌에 의한 열점 생성과 화염 전파의 가속 현상을 확인하였으며 추가적으로 평균 화학적 열 발생률이 대략 20 MJ/($g{\cdot}s$)이 되는 지점에서 최초 폭굉이 발생한다는 것을 확인하였다. 즉, 우리는 복잡한 형상에 의한 효과를 포함하는 수치적 계산 결과를 기반으로 관에서의 강한 충격파, 충격파와 화염의 상호 작용, 열점, 연소폭발천이 현상 등의 발생을 확인하였다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
• /
• pp.185-187
• /
• 2006

• 한국유체기계학회 논문집
• /
• 제5권3호
• /
• pp.40-45
• /
• 2002

Since the previous cut-and-try design algorithm requires much cost and time, the automated design technique with the CFD and optimum design algorithm has recently been concerned. In this work, the Navier-Stokes equation was solved to gain more detailed viscous flow information of cascade with rotor-stator interactions. The H-grid embedded by O-grid was generated to obtain more accurate solution by eliminating the branch cut of H-grid near airfoil surface. To handle the relative motion of the rotor to the stationary stator, the sliding multiblock method was applied and the cubic-spline interpolation was used on the block interface boundary. To validate present procedure, the time-averaged aerodynamic loads were compared with experimeatal data. A good agreement was obtained. The Modified Method of Feasible Direction (MMFD) was used to carry out the sensitivity analysis of the change of aerodynamic performance by the changes of the cascade geometry. The present optimization of the cascade gave a dramatic reduction of the drag while the lift maintains at the value within the user-specified tolerance.

• 한국전산유체공학회지
• /
• 제2권1호
• /
• pp.46-53
• /
• 1997

The flow field around a three dimensional minivan-like body has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations on a non-orthogonal curvilinear coordinate system using second-order accurate schemes for the time derivatives, and third/second-order scheme for the spatial derivatives. The Marker-and-Cell concept is applied to efficiently solve continuity equation. A H-H type of multi-block grid system is generated around a three dimensional minivan-like body. Turbulent flows have been modeled by the Baldwin-Lomax turbulent model. To validate present procedure, the flows around the Ahmed body with 12.5° of slant angle are simulated. A good agreement with other numerical results is achived. After code validation, the flows around a mimivan-like body are simulated. The simulation shows three dimensional vortex-pair just behind body. The flow separation is also observed on the rear of the body. It has concluded that the results of present study properly agreed with physical flow phenomena.

• 한국전산유체공학회지
• /
• 제17권3호
• /
• pp.25-32
• /
• 2012

This work was devoted to compare two different cavitation models to study the dependency of model constants. The cavitation model of Merkle et al.(2006) and Kunz et al.(2000) were used for the present computational study. The cavitation models were coupled with the incompressible unsteady Reynolds-Averaged Navier-Stokes solver to indicate the vaporization and condensation processes. For this purpose, a preconditioning method was added as the pseudo-time term to solve the unsteady stiffness problems. For the validation of the numerical simulation, the computation was performed for the cavitating flow in a converging-diverging channel. The present results show that Merkle's cavitation model is independent to the model constants, and the higher numerical accuracy over Kunz's cavitation model.

• 대한기계학회논문집
• /
• 제19권10호
• /
• pp.2617-2629
• /
• 1995

The flow through a centrifugal compressor rotor was calculated using the quasi-3-dimensional and fully 3-dimensional Navier-Stokes solution methods. The calculated results, obtained during the development of the computer codes for both methods are discussed. In the inviscid quasi 3-dimensional analysis, stream function formulation was used for the blade to blade (B-B) plane calculations, and the streamline curvature method was used for the meridional (H-S) plane calculations. In the viscous 3-dimensional flow analysis, a control volume method based on a general rotating curvilinear coordinate system was used to solve the time-averaged Navier-Stokes equations, and a standard k-.epsilon. model was used to obtain eddy viscosity. The quasi-3-dimensional analysis reasonably predicts the pressure distributions and requires much less computation time in the region where viscous effects are not strong; however, it fails to predict velocity field and loss mechanism through the impeller passage. The viscous 3-dimensional flow analysis shows reasonable pressure distributions and typical jet-wake flow field through the impeller passage. Secondary flow and total pressure distributions on cross-sectional planes explain the loss mechanisms through the impeller.