• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.1
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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.

• Atmosphere
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• v.34 no.2
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• pp.153-176
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• 2024

At 0843 UTC 30 May 2021, a commercial aircraft encountered severe turbulence at z = 11.5 km associated with the rapid development of Mesoscale Convective System (MCS) in the Gyeonggi Bay of Korea. To investigate the generation mechanisms of Near-Cloud Turbulence (NCT) near the MCS, Weather Research and Forecasting model was used to reproduce key features at multiple-scales with four nested domains (the finest ∆x = 0.2 km) and 112 hybrid vertical layers. Simulated subgrid-scale turbulent kinetic energy (SGS TKE) was located in three different regions of the MCS. First, the simulated NCT with non-zero SGS TKE at z = 11.5 km at 0835 UTC was collocated with the reported NCT. Cloud-induced flow deformation and entrainment process on the downstream of the overshooting top triggered convective instability and subsequent SGS TKE. Second, at z = 16.5 km at 0820 UTC, the localized SGS TKE was found 4 km above the overshooting cloud top. It was attributed to breaking down of vertically propagating convectively-induced gravity wave at background critical level. Lastly, SGS TKE was simulated at z = 11.5 km at 0930 UTC during the dissipating stage of MCS. Upper-level anticyclonic outflow of MCS intensified the environmental westerlies, developing strong vertical wind shear on the northeastern quadrant of the dissipating MCS. Three different generation mechanisms suggest the avoidance guidance for the possible NCT events near the entire period of the MCS in the heavy air traffic area around Incheon International Airport in Korea.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.141-151
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• 1997

This paper deals with a numerical study of flow-guider applied to controlling current in a bay. Two dimensional numerical model for tidal currents based on the depth averaged equation is developed and standard k-.epsilon. model is adopted to determine the turbulence diffusion. Equations are described in a generalized coordinate system to be implemented by non-staggered grid system and discretized by using finite volume method. Unsteady flow is simulated by fully implicit scheme. Hybrid scheme and central differencing are used to compute the convective terms and source terms, respectively. The tidal current in a rectangular bay is simulated and it gives satisfactory results. The realistic and distinct models of a large structure placed in bay are also exemplified with or without flow-guiders. The simulation results show that the flow-guider gives the residual tidal current in the bay by the different flux with respect to the direction of tidal current.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.27-41
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulation of three-dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence-free flow field at each physical time step. An implicit time integration method with local time stepping was implemented to accelerate the convergence in the pseudo-time sub-iteration procedure. The one-equation Spalart-Allmaras turbulence model has been adopted to solve high-Reynolds number flow fields. The flow solver was parallelized to minimize the CPU time and to overcome the computational overhead. This method has been applied to calculate steady and unsteady flow fields around submarine configurations and a 3-D infinite cylinder. Validations were made by comparing the predicted results with those of experiments or other numerical results. It was demonstrated that the present method is efficient and robust for the prediction of steady and unsteady incompressible flow fields.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.677-684
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• 2007

In the Present Study, a 3-D viscous flow solver, based on unstructured hybrid meshses containing tetrahedra, prisms and pyramids, has been developed. A finite-volume discretization scheme is used for solving the compressible Navier-Stokes equations. A cell-vertex median dual volume is used for spatial discretization. The one-equation Spalart-Allmaras turbulence model has been adopted to evaluate the eddy viscosity. Validation were made by computing laminar and turbulent flows around a 3-D wing for steady flows and turbulent flows around an oscillating 3-D wing in harmonic motion for unsteady flows.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.35-40
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• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convertive terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. In this paper k-$\varepsilon$ turbulence model with wall function is used to increase efficiency of computation times.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.3
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• pp.29-36
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• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Wavier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convective terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. Considering computation times, $\kappa$-$\varepsilon$ turbulence model with wall function is used.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.59-69
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• 2000

A numerical analysis based on two-dimensional, incompressible and compressible Navier-Stokes equations was carried out for double circular arc compressor cascade and the results are compared with available experimental data. The incompressible code based on SIMPLE algorithm adopts pressure weighted method and hybrid scheme for the convective terms. The compressible code with preconditioning method involves a upwind-biased scheme for the convective terms and LU-SGS scheme for temporal integration. Several turbulence models are evaluated by computing the turbulent viscous flows; Baldwin-Lomax, standard $\kappa$ -$\varepsilon$, $\kappa$ -$\varepsilon$ Lam. Bremhorst, standard $\kappa$-$\omega$, $\kappa$ -$\omega$ SST model.

• Journal of the Korean Society for Precision Engineering
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• v.8 no.4
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• pp.23-32
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• 1991

The paper discusses the problem of the flow over the backward facing step and the offset jet, which are calculated numerically. Standard k- .epsilon. model and its LPS modification are used as turbulence models. Hybrid central/upwind scheme and skew- upwind scheme are used as numerical schemes. The numerical scheme has a strong influence on the offset jet rather than the flow over backward facing step. The skew-upwind scheme gives good results in both cases. However, the k- .epsilon. model with LPS modification yields no remarkable improvements in the predictions of both flows. The skew-upwind scheme improves the prediction of reattachment length in the offset jet.

• Fire Science and Engineering
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• v.17 no.3
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• pp.50-54
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• 2003

The backlayer phenomena of smoke in the road tunnel is evaluated through numerical experiments. A commercial code, PHOENICS is used to simulate smoke flow in the road tunnel. The independent and dependent variables are ventilation air velocity and the length of backlayer of smoke respectively. Hybrid scheme and $textsc{k}-\varepsilon$ turbulence model is adopted in the simulation process and mass residual is used as a convergence criterion. The experimental results say that the length of backlayer is reduced linearly with the increase of ventilating air velocity and that there is a critical air velocity which prevents from the onset of backlayering phenomena. One finds that there is a fresh air region near the bottom of tunnel which could make the passenger escape from the region polluted by smoke. These phenomena come from the severe vertical stratification of the smoke air mixture in the tunnel.