• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.356-368
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• 1992

The strongly interactive flow field near a missile afterbody containing a centered exhaust jet is numerically investigated. The thin shear layer and full formulation of compressible, Reynolds I averaged Navier-Stokes equations are solved. A time-dependent implicit numericals algorithm is used to obtain solution for a variety of flow conditions. Turbulence closure is implemented by the Baldwin-Lomax algebraic eddy viscosity model. An adaptive grid technique is adopted to resolve flow regimes with large gradients and to improve the accuracy and efficiency of the computation, Numerical results show good agreemement with experimental data in all regimes.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.4
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• pp.360-369
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• 1997

We calculated the residual current forced by buoyancy, wind stress, and tidal stress in the Chinhae Bay using a three-dimensional diagnostic model. The calculated current was also compared with the observation. The flow directs outward from the central area of the Bay in the upper layer, and also forms eddy-shape stucture in the upper and middle layers. The flow of bottom layer shows an opposite pattern compared to those of top and middle layers. The maximum speed was 6.05 em/see (September) and 3.49 cm/sec (November) in the upper layer, and 4.39 cm/sec on both month in the middle layer. The Kinetic energy of November (8.39xlO' W) was larger than that of September (1.24xlO 'W), mainly resulting from larger buoyancy effect in September. In spite of the roughness of the grid size(1 km) and wind date, the calculated flow shows eorrelation(r=0.71) with the observation. We expect that the correlation be increased by increased by adopting the fine grid and the variable coefficients of diffusion and viscosity.

• 한국항공운항학회:학술대회논문집
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• 2004.11a
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• pp.240-246
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• 2004

For the prediction on the onset of oblique shock wave-induced vortex breakdown, computational studies on the Oblique Shock wave/Vortex Interaction (OSVI) are conducted and compared with both experimental results and analytic model. A Shock-stable numerical scheme, the Roe scheme with Mach number-based function (RoeM), and a two-equation eddy viscosity-transport approach are used for three-dimensional turbulent flow computations. The computational configuration is identical to available experiment, and we attempt to ascertain the effect of parameters such as a vertex strength, streamwise velocity deficit, and shock strength at a freestream Mach number of 2.49. Numerical simulations using the ${\kappa}-{\omega}SST$ turbulence model and suitably modeled vortex profiles are able to accurately reproduce many fine features through a direct comparison with experimental observations. The present computational approach to determine the criterion on the onset of oblique shock wave-induced vortex breakdown is found to be in good agreement with both the experimental result and the analytic prediction.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.51-57
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• 2001

The eddy viscosity turbulence models were applied to predict the flows through a cascade, and the prediction performances of turbulence models were assessed by comparing with the experimental results for a controlled diffusion(CD) compressor blade. The original $\kappa-\omega$ turbulence model and $\kappa-\omega$ shear stress transport(SST) turbulence model were used as two-equation turbulence model which were enhanced for a low Reynolds number flow and the Baldwin-Lomax turbulence model was used as algebraic turbulence model. Farve averaged Wavier-Stokes equations in a two-dimensional, curvilinear coordinate system were solved by an implicit, cell-centered finite-volume computer code. The turbulence quantities are obtained by lagging when the men flow equations have been updated. The numerical analysis was made to the flows of CD compressor blade in a cascade at three different incidence angles (40. 43.4. 46 degrees). We found the reversion in the prediction performance of original $\kappa-\omega$ turbulence model and $\kappa-\omega$ SST turbulence model when the incidence angie increased. And the algebraic Baldwin-Lomax turbulence model showed inferiority to two-equation turbulence models.

• International Journal of Aerospace System Engineering
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• v.2 no.2
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• pp.67-72
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• 2015

The main concern of this study is to integrate the EARSM into an industrial RANS solver in conjunction with the $k-{\omega}$ model, as proposed by Hellsten (EARSMKO2005). In order to improve the robustness, particular limiters are introduced to turbulent conservative variables, and a suitable full-approximation storage (FAS) multi-grid (MG) strategy is designed to incorporate turbulence model equations. The present limiters and MG strategy improve both robustness and efficiency significantly but without degenerating accuracy. Two discretization approachs for velocity gradient on cell interfaces are implemented and compared with each other. Numerical results of a three-dimensional supersonic square duct flow show that the proper discretization of velocity gradient improves the accuracy essentially. To assess the capability of the resulting EARSM $k-{\omega}$ model to predict complex engineering flow, the case of Common Research Model (CRM, Wing-Body) is performed. All the numerical results demonstrate that the resulting model performs well and is comparable to the standard two-equation models such as SST $k-{\omega}$ model in terms of computational effort, thus it is suitable for industrial applications.

• Journal of Hydrogen and New Energy
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• v.27 no.1
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• pp.121-126
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• 2016

Hydraulic performance of a micro-bubble pump has been analyzed by numerical simulation and experimental measurements. Flow recirculation apparatus between the pump inlet and outlet reserviors has been adopted to measure pump performance according to flow conditions sequentially. To analyze three-dimensional flow field in the micro-bubble pump, general analysis code, CFX, is employed. SST turbulence model is employed to estimate the eddy viscosity and compared the pump performance to k-${\varepsilon}$ model. Unstructured grids are used to represent a composite grid system including blade, casing and inlet casing. It is found that the numerical model used in the present study is effective to evaluate the pump performance. From the numerical simulation, low velocity region due to pressure loss is decreased where pump efficiency has maximum value. Detailed flow field inside the micro-bubble pump is also analyzed and compared.

• Journal of the korean society of oceanography
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• v.37 no.3
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• pp.169-177
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• 2002

An eddy-resolving free-surface primitive-equation model with nonlinear terrain-following coordinates is established to study the exchange of water masses among the Asian marginal seas and their adjacent waters. A curvilinear coordinate system is used to generate the horizontal grid with a variable resolution for the regional oceans from $5^{\circ}$S to $45^{\circ}$N and $100^{\circ}$E to $155^{\circ}$E. The higher resolution region has about a 10 km by 10 km grid covering the complex geometry of the coastal marginal seas, while the lower resolution region has about a 30 km by 30 km grid covering the eastern Pacific. The model is initialized by the Levitus annual climitology and forced by the monthly mean air-sea fluxes of momentum, heat, and freshwater derived from the Comprehensive Ocean-Atmosphere Data Set. High-resolution and low-viscosity are identified as the key factors for a better representation of the exchange of waters through narrow straits and passages between the marginal seas and their adjacent waters. The dynamics of the loop currents and eddies in the South China Sea and Celebes Sea are examined in detail. It has found that the anticyclonic loop and detached eddies from the Kuroshio through the Luzon Strait play an important role in transporting warm and salty water into the South China Sea, while the cyclonic circulation of the Mindanao Current in the Celebes Sea plays a role in contributing cold water to the Indonesian throughflow. The deep undercurrent of the western Pacific is shown to provide fresher water to the South China Sea and Celebes Sea. These modeling results suggest that the exchange processes via the narrow straits and passages are of fundamental importance to the maintenance of water masses for the marginal sea region.

• Ocean Systems Engineering
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• v.6 no.1
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• pp.23-60
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• 2016

The major objective of this study was to develop further understanding of 3D nearshore hydrodynamics under a variety of wave and tidal forcing conditions. The main tool used was a comprehensive 3D numerical model - combining the flow module of Delft3D with the WAVE solver of XBeach - of nearshore hydro- and morphodynamics that can simulate flow, sediment transport, and morphological evolution. Surf-swash zone hydrodynamics were modeled using the 3D Navier-Stokes equations, combined with various turbulence models (${\kappa}-{\varepsilon}$, ${\kappa}-L$, ATM and H-LES). Sediment transport and resulting foreshore profile changes were approximated using different sediment transport relations that consider both bed- and suspended-load transport of non-cohesive sediments. The numerical set-up was tested against field data, with good agreement found. Different numerical experiments under a range of bed characteristics and incident wave and tidal conditions were run to test the model's capability to reproduce 3D flow, wave propagation, sediment transport and morphodynamics in the nearshore at the field scale. The results were interpreted according to existing understanding of surf and swash zone processes. Our numerical experiments confirm that the angle between the crest line of the approaching wave and the shoreline defines the direction and strength of the longshore current, while the longshore current velocity varies across the nearshore zone. The model simulates the undertow, hydraulic cell and rip-current patterns generated by radiation stresses and longshore variability in wave heights. Numerical results show that a non-uniform seabed is crucial for generation of rip currents in the nearshore (when bed slope is uniform, rips are not generated). Increasing the wave height increases the peaks of eddy viscosity and TKE (turbulent kinetic energy), while increasing the tidal amplitude reduces these peaks. Wave and tide interaction has most striking effects on the foreshore profile with the formation of the intertidal bar. High values of eddy viscosity, TKE and wave set-up are spread offshore for coarser grain sizes. Beach profile steepness modifies the nearshore circulation pattern, significantly enhancing the vertical component of the flow. The local recirculation within the longshore current in the inshore region causes a transient offshore shift and strengthening of the longshore current. Overall, the analysis shows that, with reasonable hypotheses, it is possible to simulate the nearshore hydrodynamics subjected to oceanic forcing, consistent with existing understanding of this area. Part II of this work presents 3D nearshore morphodynamics induced by the tides and waves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.772-778
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• 2002

A numerical analysis of turbulent gas-particle two-phase flow is performed in conjunction with the experiments of Fackrell ＆ Robins and Raupach & Legg that considered ground-level source and/or elevated source flat plate flow. K-$\omega$ turbulence model is used in order to analyze fully turbulent flow field and the concentration equation with settling velocity is adopted for the concentration field. The model of Einstein and Chien is applied that couples the velocity field and the concentration field. Turbulent eddy viscosity is re-evaluated in this model. The present numerical results have good agreement between the simulation and the experimental data for the mean flow velocities and particle concentrations. While the previous study shows about 27% error in the vicinity of the source of particle concentration, the .present study allows about 14% error. A new turbulent gas-particle flow model developed by this study is able to cut down error by 13% at a near source.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1661-1670
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• 1996

Incompressible flow over a backward-facing step is computed by low Reynolds number turbulence models in order to compare with direct simulation results. In this study, selected low Reynolds number 1st and 2nd (Algebraic Stress Model : ASM) moment closure turbulence models are adopted and compared with each other. Each turbulence model predicts different flow characteristics, different re-attachment point, velocity profiles and Reynolds stress distribution etc. Results by .kappa.-.epsilon. turbulence models indicate that predicted re-attachment lengths are shorter than those by standard model. Turbulent intensity and eddy viscosity by low Reynolds number .kappa.-.epsilon. models are still greater than DNS results. The results by algebraic stress model (ASM) are more reasonable than those by .kappa.-.epsilon. models. The convective scheme is QUICK (Quadratic Upstream Interpolation for Convective Kinematics) and SIMPLE algorithm is adopted. Reynolds number based on step height and inlet free stream velocity is 5100.