• Wind and Structures
• /
• v.25 no.6
• /
• pp.537-549
• /
• 2017

In this study, the turbulent flow around a bluff body for different wind velocities was investigated numerically by using its two- and three-dimensional models. These models were tested to verify the validity of the simulation by being compared with experimental results which were taken from the literature. Variations of non-dimensional velocities in different positions according to the bluff body height were analysed and illustrated graphically. When the velocity distributions were examined, it was seen that the results of both two- and three-dimensional models agree with the experimental data. It was also seen that the velocities obtained from two-dimensional model matched up with the experimental data from the ground to the top of the bluff body. Particularly, compared to the front part of the bluff body, results of the upper and back part of the bluff body are better. Moreover, after comparing the results from calculations by using different models with experimental data, the effect of multidimensional models on the obtained results have been analysed for different inlet velocities. The calculation results from the two-dimensional (2D) model are in satisfactory agreement with the calculation results of the three-dimensional model (3D) for various flow situations when comparing with the experimental data from the literature even though the 3D model gives better solutions.

• Wind and Structures
• /
• v.31 no.4
• /
• pp.351-362
• /
• 2020

In this study, the impact of roof slope on the flow characteristics over low-sloped gable roofs was investigated using steady computational fluid dynamics (CFD) simulations based on a k-ω SST turbulence model. A measurement database of the flow field over a scaled model of 15° was created using particle image velocimetry (PIV). Sensitivity analyses for the grid resolutions and turbulence models were performed. Among the three common Reynolds-averaged Navier-Stokes equations (RANS) models, the k-ω SST model exhibited a better performance, followed by the RNG model and then the realizable k-ε model. Next, the flow properties over the differently sloped (0° to 25°) building models were determined. It was found that the effect of roof slope on the flow characteristics was identified by changing the position and size of the separation bubbles, 15° was found to be approximately the sensitive slope at which the distribution of the separation bubbles changed significantly. Additionally, it is suggested additional attention focused on the distributions of the negative pressure on the windward surfaces (especially 5° and 10° roofs) and the possible snow redistribution on the leeward surfaces.

• 한국전산유체공학회:학술대회논문집
• /
• 2007.04a
• /
• pp.87-90
• /
• 2007

A general purpose program NUFLEX for the analysis 3-D thermo/fluid flow and pre/post processor in complex geometry has been developed, which consists of a flow solver based on FVM and GUI based pre/post processor. The solver employs a general non-orthogonal grid system with structured grid and solves laminar and turbulent flows with standard/RNG ${\kappa}-{\varepsilon}\;SST$ turbulence model. In addition, NUFLEX is incorporated with various physical models, such as interfacial tracking, cavitation, MHD, melting/solidification and spray model. For the purpose of verification of the program and testing the applicability, many actual problems are solved and compared with the available data. Comparison of the results with that by STAR-CD or FLUENT program has been also made for the same flow configuration and grid structure to test the validity of NUFLEX.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.502-507
• /
• 2003

Spiral jet is characterized by a wide region of the free vortex flow with a steep axial velocity gradient, while swirl jet is largely governed by the forced vortex flow and has a very low axial velocity at the jet axis. However, detailed generation mechanism of spiral flow components is not well understood, although the spiral jet is extensively applied in a variety of industrial field. In general, it is known that spiral jet is generated by the radial flow injection through an annular slit which is installed at the inlet of convergent nozzle. The objective of the present study is to understand the flow characteristics of the spiral jet, using a computational method. A finite volume scheme is used to solve 3-dimensional Navier-Stokes equations with RNG ${\kappa}-{\varepsilon}$ turbulent model. The computational results are validated by the previous experimental data. It is found that the spiral jet is generated by coanda effect at the inlet of the convergent nozzle and its fundamental features are dependent the pressure ratio of the radial flow through the annular slit and the coanda wall curvature.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.155-159
• /
• 2011

본 연구는 만곡수로 외측에 횡월류 위어를 설치하여 곡률반경에 대한 횡월류 유량계수의 특성을 분석하였다. 곡률반경의 변화에 따른 만곡부의 중심각이 180인 수로모형을 설계하였으며, FLOW-3D모형에 적용하여 유량계수를 산정하고 직선 수로와 비교하여 유량계수의 특성을 분석하는데 목적이 있다. 난류모형은 RNG-$\in$ 모형을 사용하였으며, 수치기법으로는 유한체적법을 사용하였다. 모형의 적용성 검정을 위해 기존에 연구되었던 수리실험과 동일한 조건의 수치모의를 수행하여 모형의 적용성을 확인하였다. 본 연구에서는 하폭를 고정시키고 곡률반경를 변화시킴으로써 $R_c/b$의 변화에 따른 유량계수(C)의 변화를 분석하고, 만곡수로의 월류량($Q_{wc}$)에 대한 직선수로의 월류량($Q_{ws}$)의 비, 만곡수로의 평균 월류 수심에 대한 직선수로의 평균 월류 수심($y_{cave}/y_{save}$)과 $R_c/b$의 관계를 분석하였다. 분석결과 유량계수는 상류수심, 월류량, 만곡수로의 곡률반경 등의 변화에 따라 유량계수는 변화하였으며, 직선과 만곡수로에 대해 분석을 수행하였기 때문에 직선수로의 영향인자를 이용하여 만곡수로에 설치된 횡월류 위어의 월류량과 유량계수를 추정 가능할 것이라 판단된다.

• Journal of ILASS-Korea
• /
• v.21 no.1
• /
• pp.47-52
• /
• 2016

This paper describes the modeling of CNG direct injection using gaseous sphere injection model. Simulation of CNG direct injection does not need break up and evaporation model compared to that of liquid fuel injection. And very fine mesh is needed near the injector nozzle to resolve the inflow boundary. Therefore it takes long computation time for gaseous fuel injection simulation. However, simulation of CNG direct injection could be performed with the coarse mesh using gaseous sphere injection model. This model was integrated in KIVA-3V code and RNG $k-{\varepsilon}$ turbulence model needs to be modified because this model tends to over-predict gas jet diffusion. Furthermore, we preformed experiments of gaseous fuel injection using PLIF (planar laser induced fluorescence)method. Gaseous fuel injection model was validated against experiment data. The simulation results agreed well with the experiment results. Therefore gaseous sphere injection model has the reliability about gaseous fuel direct injection. And this model was predicted well a general tendency of gaseous fuel injection.

• Journal of Power System Engineering
• /
• v.18 no.3
• /
• pp.59-65
• /
• 2014

The computational fluid dynamics was carried out to evaluate turbulent models on the swirling flow of a gun-type gas burner(GTGB) according to the mesh size. The commercial SC/Tetra software was used for a steady-state, incompressible and three-dimensional numerical analysis. In consequence, the velocity magnitude from the exit of a GTGB and the flowrate predicted by the turbulent models of MP k-${\varepsilon}$, Realizable k-${\varepsilon}$ and RNG k-${\varepsilon}$ agree with the results measured by an experiment very well. Moreover, the turbulent kinetic energy predicted by the turbulent model of standard k-${\varepsilon}$ with mesh type C only agrees with the experimental result very well along the radial distance. On the other hand, the detailed prediction of the information of swirling flow field near the exit of a GTGB at least needs a CFD analysis using a fairly large-sized mesh such as a mesh type C.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.15 no.3
• /
• pp.239-249
• /
• 2005

Ventilation effect is analyzed for boiler building with multiple heat sources. Air flow inside the boiler building is characterized as turbulent mixed convection. Analysis methodology is set up with two different $k-{\varepsilon}$ type models (standard $k-{\varepsilon}$, RNG $k-{\varepsilon}$). Two different cases with high and low outside temperature are analyzed. In case of high outside temperature condition, mixed convection is well realized inside the boiler building. With different upper louver opening rate, air flow is also well established and proper opening rate is found to meet design limit in case of low outside temperature condition. Difference of analysis results for two different turbulence models are not significant. Therefore, analysis methodology with simple $k-{\varepsilon}$ turbulence model is found to be reliable for the boiler building ventilation analysis. However, more simplified geometrical model is desired to expand its application.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.4
• /
• pp.118-129
• /
• 1996

In this study, three dimensional flow analysis in a HVAC duct was performed computationally using various turbulence models and compared numerical predictions such as outlet flow split, surface pressure distribution along the duct to experimental data. It's well known that accuracy of computational predictions of flow heavily dependent on turbulent models and discritization method. Therefore, in this work, to assess the ability of turbulent models to predict characteristics of duct flow, three kinds of models, namely standard $k-\varepsilon$, RNG $k-\varepsilon$ and modified $k-\varepsilon$, containing parameter for the effect of streamline curvature were employed and validated one another by comparing with experimental data. In results, modified $k-\varepsilon$ turbulence model allows a successful prediction of static pressure distribution particulary at around strong curvature but little improvement flow split. In the futrue, adoption of CFD to design HVAC duct with modified $k-\varepsilon$ model will bring benefits of producing more accurate prediction, and also give designers more detail information much more than now.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.8 no.3
• /
• pp.181-189
• /
• 2000

The aerodynamic characteristics of large transport vehicle has become more and more important in recent vehicle design to improve driving performance in high speed cruising and raise the product valve with regard to a comfortable driving condition. Hence, detailed knowledge of the flow field around truck coner vane is essential to improve fuel efficiency and reduce the dirt contamination on vehicle body surface. In this study, three-dimensional flow characteristics around corner vane attached to truck cabin were computed for the steady, incompressible, and high speed viscous flow, adopting the RNG k-$\varepsilon$ turbulence model. In order to investigate the influence of configuration and structure of corner vane, computations were carried out for four cases at a high Reynolds number, Re=4.1$\times$106 (based on the cabin height). The global flow patterns, drag coefficient and the distributions such as velocity magnitude, turbulent kinetic energy around the corner vane, were examined. As a result of this study, we could identify the flow characteristics around corner vane for the variation of corner vane length and width. Also, suggest the improved structure to reduce the dirt contamination in cabin side.