• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.90-98
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• 1998

본 논문은 2차원 해면효과의 수치계산 결과를 정리하였다. 지면으로부터의 높이변화에 따른 점성유동장을 계산하기 위하여 지배방정식으로는 비압축성 RANS방정식을, 시간에 대하여 서는 음해법으로 프로그램을 구성하였다. 압력항은 가상압축성을 도입 4차 수치확산항을 추가하는 것에 의해 계산하였으며, 높은 레이놀즈수에서의 효과적인 계산을 위해 Baldwin-Lomax 난류 모델을 도입하였다. 해면효과가 없는 무한유중에서의 NACA-0012단면 계산결과를 실험데이터와 비교하는 것에 의해 프로그램의 타당성을 확인하였다. NACA-6409와 두께비 $4.6\%$의 날개에 대하여 해면효과를 고려한 계산을 수행하였다. 높이의 변화에 따라 계산된 무차원계수, 압력 및 속도분포는 해면효과의 특성을 잘 보여주고 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.781-785
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• 2003

This work presents a numerical analysis of two-phase natural circulation flow in reactor cavity under external vessel cooling. Steady, incompressible, three-dimensional Reynolds-averaged Navier-Stokes equations for multiphase flows with zero equation turbulence model are solved to predict the shear key effect on the circulation rate of cooling water and the distribution of void fraction according to the different mass flow of inlet air. Results show that shear key has a positive effect on the circulation rate of cooling water and induce a local increase of void fraction below the shear key, but not remarkably.

• International Journal of Fluid Machinery and Systems
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• 제8권1호
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• pp.36-45
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• 2015

Oil and gas industry pumps viscous fluids and investigation of flow physics is important to understand the machine behavior to deliver such fluids. 3D numerical flow simulation and analysis for different viscous fluids at different rotational speeds of a centrifugal impeller have been reported in this paper. Reynolds-averaged Navier Stokes (RANS) equations were solved and the performance analysis was made. Standard two equation k-${\varepsilon}$ model was used for the turbulence closure of steady incompressible flow. An inlet recirculation and reverse flow in impeller passage was observed at low impeller speeds. It was also found that the higher viscosity fluids have higher recirculation which hinders the impeller performance.

• 설비공학논문집
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• 제11권1호
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• pp.73-80
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• 1999

This paper describes a numerical study of three-dimensional buoyant turbulent flow in a stairwell model with three convective differencing schemes, which include the upwind differencing scheme, the hybrid scheme and QUICK scheme. The Reynolds-averaged Navier-Stokes and energy equations are solved with a two-equation turbulence model. The Boussinesq approximation is used to model buoyancy terms in the governing equations. Three-dimensional predictions of the velocity and temperature fields are presented and are compared with experimental data. Three-dimensional simulations with each scheme have predicted the overall features of the flow fairly satisfactorily. A better agreement with experimental is achieved with QUICK scheme.

• 대한조선학회논문집
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• 제38권4호
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• pp.1-10
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• 2001

비 압축성 점성 유동에 대한 RANS 방정식의 수치 해법을 사용해서 4상한(four quadrant) 조건에서 작동하는 박용 프로펠러 주위의 난류 유동과 프로펠러 단독 성능을 계산하였다. 4상한 조건의 단독 성능에 대한 실험결과가 존재하는 모형 프로펠러 P4381에 대하여 계산된 유동은 다양한 조건에서 프로펠러에 발생하는 3차원 유동박리를 포함한 복잡한 점성유동 특성을 잘 보여주었으며, 계산된 프로펠러 추력과 토크는 실험에서 캐비테이션이 심하게 발생된 일부 경우를 제외하고는 실험 결과와 잘 일치하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.66-72
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• 1999

A numerical simulation method has been under development for solving turbulent flows around a ship model in maneuvering motion using the Reynolds Averaged Navier-Stokes equations. The method used second-order finite differences, collocated grids, pressure-Poisson equation and four-stage Runge-Kutta scheme as key components of the solution method. A modified Baldwin-Lomax model is used for the turbulence closure. This paper presents a preliminary result of the computational study on turbulent flows past a ship model in drift motion. Calculations are carried out for a Series 60 $C_B=0.6$ ship model, for which detailed experimental data are available. The results of the present calculations are compared with the experimental data for hydrodynamic forces acting on the model as well as velocity distributions at longitudinal sections. Only fair agreements has been achieved. The computational results show the complex asymmetrical shear flow patterns including three-dimensional separations followed by formation of bilge vortices both in bow and stern regions.

• 한국전산유체공학회지
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• 제12권4호
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• pp.85-89
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• 2007

In the present work, flow analysis has been performed for side channel type double stage ring blower by solving three-dimensional Reynolds-averaged Navier-Stokes equation. Shear stress transport model is used as turbulent closure. The commercial CFD code CFX 11.0 is used for the calculations. Each of two stage is calculated separately and the second stage inlet flow is same as the first stage outlet flow so that consecutive calculation is possible. Velocity and pressure fields have been analyzed at the mid-plane between blades. The numerical results are validated with experimental data for head coefficients at different flow coefficients.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.257-261
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• 2004

Computational fluid dynamics analysis was carried out for thermo-chemical flow field in Arcjet thruster with mono-propellant Hydrazine ($N_2$H$_4$) as a working fluid. The theoretical formulation is based on the Reynolds Averaged Navier-Stokes equations for compressible flows with thermal radiation. The electric potential field governed by Maxwell equation is loosely coupled with the fluid dynamics equations through the Ohm heating and Lorentz force. Chemical reactions were assumed being infinitely fast due to the high temperature field inside the arcjet thruster. An equilibrium chemistry module for nitrogen-hydrogen mixture and a thermal radiation module for optically thin media were incorporated with the fluid dynamics code. Thermo-physical process inside the arcjet thruster was understood from the flow field results and the performance prediction shows that the thrust force is increased by amount of 3 times with 0.6KW arc heating.

• 대한기계학회논문집B
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• 제25권2호
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• pp.269-276
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• 2001

This paper dipicts the computational results for the axisymmetric subsonic/sonic ejector systems with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-Averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the ejector diffuser exit. In order to obtain practical design factors for subsonic/sonic ejector systems, the ejector throat area, the mixing section configuration, and the ejector throat length were changed in computations. For the subsonic/sonic ejector systems operating in the range of low operation pressure ratio, the effects of the design factors on the flow are discussed.

• 한국해안·해양공학회논문집
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• 제31권6호
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• pp.409-422
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• 2019

Beach cusp의 생성기작으로 기능하는 Synchronous Edge wave의 수리특성을 살펴보기 위한 3D 수치모의를 OpenFOAM 기반 tool box인 IHFOAM을 활용하여 수행하였다. 파랑모형은 RANS[Reynolds Averaged Navier-Stokes equation]와 연속방정식으로 구성하였으며, Synchronous Edge wave 형성에 필요한 연안방향으로 파고가 변조되는 short-crested waves는 동일한 주기와 파고를 지니는 두 개의 Cnoidal wave가 전면 해역에서 비스듬히 조우되도록 조파하여 재현하였다. 모의결과 파랑 집중단면에서의 유속이 파랑 분산단면보다 전체적으로 크게 모의되었다. 또한 파랑 집중단면의 경우 해안방향 흐름[up-rush]이 먼 바다방향 흐름[back-wash]보다 세기는 우월하나 지속기간은 짧은 비선형 파동계의 일반적인 성정을 지니는 것으로 모의되었다. 이와 더불어 처오름 정점에서 양쪽의 분산단면으로 흐름이 나뉘며 약해지는 b ack-wash로 인해 up-rush 최대유속은 back-wash 최대유속의 두 배 가까이 증가하는 것으로 관측되었다. 이에 비해 파랑 분산단면의 경우 집수효과로 해안 인근 수역에서는 먼 바다방향 흐름이 해안방향흐름보다 우월하게 모의되었다. 또한 천수 중간 수역에서는 해안방향 흐름이 여전히 우세하나 비대칭 정도는 현저하게 감소하였다. 이러한 수리특성은 Synchronous Edge wave의 전형적인 성정으로 수치모의가 성공적으로 이루어진 것으로 판단된다. 이 과정에서 너울이 우월한 해양환경에서 해빈이 느리지만 점진적으로 복원되는 과정에서 주 기작으로 기능하는 경계층 streaming에 대한 새로운 해석도 제시되었다.