• 대한조선학회지
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• 제18권2호
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• pp.7-20
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• 1981

A method to predict the three-dimensional turbulent boundary layer on ship forms is introduced. The present differential method is in the scope of thin boundary layer theory and adopting the eddy-viscosity turbulence model. Two different numerical schemes are taken in this paper to handle the sign-changing cross-flows. The method is applied to predict the boundary layer development on real ship forms; SSPA Model 720($C_B$=0.675) and HSVA Tanker Model($C_B$=0.85). The results are qualitatively in good agreements with measurements except at the very stern. Therefore the method seems to be very promising if further developments are accomplished to handle the thick stern boundary layer effectively.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.187-193
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• 2007

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}\;-\;{\omega}$ turbulence model. The cavity has the aspect ratios of 2.5, 3.5 and 4.5 for two-dimensional case, same aspect ratios with the W/D ratio of 2 for three-dimensional case. The Mach and Reynolds numbers are 0.53 and 1,600,000 respectively. The flow field is observed to oscillate in the "shear layer mode" with a feedback mechanism. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formula. The MPI(Message Passing Interface) parallelized code was used for calculations by PC-cluster.

• Journal of Advanced Marine Engineering and Technology
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• 제30권5호
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• pp.580-588
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• 2006

Two-dimensional turbulent flows past a square cylinder and cavity noise are simulated by the finite difference lattice Boltzmann method with subgrid turbulence model. The method, based on the standard Smagorinsky subgrid model and a single-time relaxation lattice Boltzmann method, incorporates the advantages of FDLBM for handling arbitrary boundaries. The results are compared with those by the experiments carried out by Noda & Nakayama and Lyn et al. Numerical results agree with the experimental ones. Besides, 2D computation of the cavity noise generated by flow over a cavity at a Mach number of 0.1 and a Reynolds number based on cavity depth of 5000 is calculated. The computation result is well presented a understanding of the physical phenomenon of tonal noise occurred primarily by well-jet shear layer and vortex shedding and an aeroacoustic feedback loop.

• International Journal of Aeronautical and Space Sciences
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• 제17권1호
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• pp.8-19
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• 2016

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ${\omega}RSM$ turbulence model. Additionally, the RNG $k-{\varepsilon}$, SSG RSM, and $SST_+{\gamma}-Re_{\theta}$ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ${\omega}RSM$ results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The $SST_+{\gamma}-Re_{\theta}$ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

• Wind and Structures
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• 제15권3호
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• pp.247-261
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• 2012

Some numerical investigations are presented concerning the response of a given plate under turbulence driven excitations. Three different input loads are simulated according to the wall pressure distributions derived from the models proposed by Corcos, Efimtsov and Chase, respectively. Modal solutions (finite element based) are used for building the modal stochastic responses in the sub-critical aerodynamic frequency range. The parametric investigations concern two different values of the structural damping and three values of the boundary layer thickness. A final comparison with available experimental data is also discussed. The results demonstrate that the selection of the adequate TBL input model is still the most critical step in order to get a good prediction.

• Nuclear Engineering and Technology
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• 제56권2호
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• pp.611-623
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• 2024

The ISP-47 TOSQAN experiment was analyzed with containmentFOAM which is an open-source CFD code based on OpenFOAM. The containment phenomena taking place during the experiment are gas mixing, stratification and wall condensation in a mixture composed of steam and non-condensable gas. The k-ω SST turbulence model was adopted with buoyancy turbulence models. The wall condensation model used is based on the diffusion layer approach. We have simulated the full TOSQAN experiment which had a duration 20000 s. Sensitivity studies were conducted for the buoyancy turbulence models with SGDH and GGDH and there were not significant differences. All the main features of the experiments namely pressure history, temperature, velocity and gas species evolution were well predicted by containemntFOAM. The simulation results confirmed the formation of two large flow stream circulations and a mixing zone resulting by the combined effects of the condensation flow and natural convection flow. It was found that the natural convection in lower region of the vessel devotes to maintain two large circulations and to be varied the height of the mixing zone as result of sensitivity analysis of non-condensing wall temperature. The computational results obtained with the 2D mesh grid approach were comparable to the experimental results.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 추계 학술대회논문집
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• pp.182-187
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• 2003

Numerical analysis of three-dimensional vicous flow is used to compute the design speed operating line of a transonic axial-flow compressor. The Navier-Stokes equation was solved by an explicit finite-difference numerical scheme and the Baldwin-Lomax turbulence model was applied. A spatially-varying time-step and an implicit residual smoothing were used to improve convergence. Two-stage axial compressor of a turboshaft engine developed KARI was chosen for the analysis. Numerical results show reasonably good agreements with experimental measurements made by KARI. Numerical solutions indicate that there exist a strong shock-boundary layer interaction and a subsequent large flow separation. It is also observed that the shock is moved ahead of the blade passage at near-stall condition.

• 대한기계학회논문집
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• 제13권5호
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• pp.1052-1060
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• 1989

본 연구에서는 0-방정식 난류모형과 2-방정식 난류모형 그리고 역압력 구배와 수렴과 발산의 영향을 고려한 2-방정식 난류모형을 사용하여 대칭단면에서의 난류유동 을 해석하고, 계산 결과를 비교하여 난류모형의 적절성을 평가하고자 한다.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권3호
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• pp.117-128
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• 2002

This paper describes the smoke filling process of a fire field model based on a self-deve-loped SMEP (Smoke Movement Estimating Program) code to the simulation of fire induced flows in the two types of atrium space containing a ceiling heat flux. The SMEP using PISO algorithm solves conservation equations for mass, momentum, energy and species, together with those for the modified k-$\varepsilon$ turbulence model with buoyancy production term. Also it solves the radiation equation using the discrete ordinates method. Compressibility is assumed and the perfect gas law is used. Comparison of the calculated upper-layer average tempera-ture and smoke layer clear height with the zone models has shown reasonable agreement. The zone models used are the CFAST and the NBTC one-room. For atrium fires with ceiling glass the ceiling heat flux by solar heat causes a high smoke temperature near the ceiling. However, it has no effect on the smoke movement such as the smoke layer clear heights that are important in fire safety. In conclusion, the smoke layer clear heights that are important in evacuation activity except the early of a fire were not as sensitive as the smoke layer tem-perature to the nature of ceiling heat flux condition. Thus, a fire sensor in atrium with ceiling glass has to consider these phenomena.

• Wind and Structures
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• 제15권1호
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• pp.17-26
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• 2012

Modeling swirling wakes is of considerable interest to wind farm designers. The present work is an attempt to develop a computational tool to understand free, far-wake development behind a single rotating wind turbine. Besides the standard momentum and continuity equations from the boundary layer theory in two dimensions, an additional equation for the conservation of angular momentum is introduced to study axisymmetric swirl effects on wake growth. Turbulence is simulated with two options: the standard ${\kappa}-{\varepsilon}$ model and the Reynolds Stress transport model. A finite volume method is used to discretize the governing equations for mean flow and turbulence quantities. A marching algorithm of expanding grids is employed to enclose the growing far-wake and to solve the equations implicitly at every axial step. Axisymmetric far-wakes with/without swirl are studied at different Reynolds numbers and swirl numbers. Wake characteristics such as wake width, half radius, velocity profiles and pressure profiles are computed. Compared with the results obtained under similar flow conditions using the computational software, FLUENT, this far-wake model shows simplicity with acceptable accuracy, covering large wake regions in far-wake study.