• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2666-2671
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• 2007

This work presents microchannel heat sink shape optimization procedure using Kriging method. Design variables relating to microchannel width, depth and fin width are selected, and thermal resistance has been taken as objective function. Design points are selected through a three-level fractional factorial design of sampling method. Navier-Stokes and energy equations for laminar flow and conjugate heat transfer are solved at these design points using a finite volume solver. Solutions are carefully validated with experimental results. Using the numerically evaluated objective function, a surrogate model (Kriging) is constructed and optimum point is searched by sequential quadratic programming. The process of shape optimization greatly improves the thermal performance of microchannel heat sink under constant pumping power.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.20-26
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• 2008

A numerical study is carried out to analyze the steady three-dimensional turbulent flow and convective heat transfer in a staggered pin-fin array with diamond shaped elements at various geometrical configurations. Steady Reynolds-averaged Navier-Stokes equations and energy equation are solved using a finite volume based solver. Shear stress transport (SST) model is used as turbulence closure. The computational domain is composed of one pitch of pin-fin displacement with periodic boundary conditions on the surfaces normal to the streamwise direction and the cross-streamwise direction. The numerical results for Nusselt number and friction factor are validated with experimental results. The effects of pin angle, pin height and pitch on Nusselt number, friction factor and efficiency index are investigated.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.177-184
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• 2009

Cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has focused on the simulation of cavitating flow past cylinders with strong side flows. The governing equation is the Navier-Stokes equation based on the homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved liquid and vapor phase, separately. An implicit dual time and preconditioning method are employed for computational analysis. For the code validation, the results from the present solver have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results have been obtained. After the code validation, the strong side flow was applied to include the wake flow effects of the submarine or ocean tide.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.3 no.2
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• pp.161-171
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• 1999

Aerodynamic sensitivity analysis codes are developed via the hand-differentiation using a direct differentiation method and an adjoint method respectively from discrete two-dimensional compressible Navier-Stokes equations. Unlike previous other researches, Baldwin-Lomax algebraic turbulence model is also differentiated by hand to obtain design sensitivities with respect to design variables of interest in turbulent flows. Discrete direct sensitivity equations and adjoint equations are efficiently solved by the same time integration scheme adopted in the flow solver routine. The required memory for the adjoint sensitivity code is greatly reduced at the cost of the computational time by allowing the large banded flux jacobian matrix unassembled. Direct sensitivity code results are found to be exactly coincident with sensitivity derivatives obtained by the finite difference. Adjoint code results of a turbulent flow case show slight deviations from the exact results due to the limitation of the algebraic turbulence model in implementing the adjoint formulation. However, current adjoint sensitivity code yields much more accurate sensitivity derivatives than the adjoint code with the turbulence eddy viscosity being kept constant, which is a usual assumption for the prior researches.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.223-232
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• 1998

To investigate the flow inside the centrifugal impeller, computer program which can solve Three-dimensional compressible turbulent flow has been developed. The Navier-Stokes equations were chosen as the governing equation for viscous flow while Euler equations for inviscid case. Time marching method was incorporated with the Flux Difference Splitting method suggested by Roe to capture the steep gradients such as a shock. For high order of accuracy, MUSCL approach was adopted while differentiable limiter to ensure TVD property. For turbulence closure, Baldwin- Lomax model was applied due to its simplicity. To demonstrate the capabilities of present program, several validation problems have been solved and compared with experiments and other available data. From the above calculations generally good agreements were obtained. Finally, the developed code was applied to Eckardt's impeller and the performance prediction was carried out. Some important aspects on boundary condition for successful simulation were discussed and the remedy was also introduced.

• Journal of computational fluids engineering
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• v.5 no.3
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• pp.23-31
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• 2000

The three-dimensional unsteady compressible Full Navier-Stokes equation solver with sliding multi-block method has been applied to analyze three dimensional characteristics of the viscous flow field and compression wave around the high speed train which is entering into a tunnel. The numerical scheme of AF + ADI was used to efficiently solve Navier-Stokes equations in the curvilinear coordinate system. The vortex formation owing to the viscous interaction around the train was found and the generation of compression wave due to the blockage effects was observed ahead of the train in the form of plane wave. The three dimensional characteristics of the flow field compared to the analytic results were discussed in detail. The variation of pressure of tunnel wall surface and velocity profile of the train are identified as the train enters into a tunnel. The changes in aerodynamic forces and streamlines of each specific sections are also discussed.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.60-66
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• 2011

Engineering interests of submerged bodies and turbomachinery has led researchers to study various cavitation models for decades. The governing equations used for the present work are the two-phase Navier-Stokes equations with homogeneous mixture model. The solver employed on implicit dual time preconditioning algorithm in curvilinear coordinates. Three different cavitation models were applied to two axisymmetric cylinders and compared with experiments. It is concluded that the Merkle's new cavitation model has successfully accounted for cavitating flows and well captured the re-entrant jet phenomenon over the 0-caliber cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.9
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• pp.733-740
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• 2007

Microchannel heat sink shape optimization is performed using Kriging method. Design variables relating to microchannel width, depth and fin width are selected, and thermal resistance has been taken as objective function. Design points are selected through a three-level fractional factorial design of sampling method. Navier-Stokes and energy equations for laminar flow and conjugate heat transfer are solved at these design points using a finite volume solver. Solutions are carefully validated with experimental results. Using the numerically evaluated objective function, a surrogate model (Kriging) is constructed and optimum point is searched by sequential quadratic programming. The process of shape optimization greatly improves the thermal performance of microchannel heat sink under constant pumping power.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.29-34
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• 2000

This paper describes a numerical study to make clear the characteristics of flow around a high speed catamaran hull advancing on calm water. The simulation is carried out at Froude number of 0.5 with a separation to length rations of 0.2 to 0.5. To simulate the flows, the Navier-Stokes solver is employed in which the free surface condition is included. Computations are performed in a rectangular grid system based grid system based on the Marker & Cell method. For the validation, the computation results are compared with the experiments.

• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.150-161
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• 1993

원초변수를 이용한 Navier-Stokes 방정식의 수치계산기법을 개발하고, 이를 응용하여 backward facing step의 층류 유동을 계산하였다. 직교좌표계에서의 비압축성 Navier-Stokes방정식을 풀기위해 시간과 공간항을 2차 정도의 유한 차분을 사용하여 이산화하였고 비교차격자계를 사용하여 양해법으로 수치 계산하였다. 운동량방정식과 연속방정식으로 부터 유도된 압력방정식(pressure-poisson equation)을 이용하여 무발산 조건을 만족시켰ㄲ다. Backward facing step의 층류 유동을 100.$\leq$R$_e$$\leq$1000 범위에 대해서 수치 계산하였으며 실험결과와 잘 일치하는 결과를 구할 수 있었다. 특히 step뒤에서 생기는 박리구간의 길이는 다른 계산결과들보다 실험치에 가까운 값을 얻을 수 있었으며, Re가 600보다 클때는 위쪽 벽에 또 다른 박리 유동이 발생되는 현상이 예측되었다.