• Journal of computational fluids engineering
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• v.16 no.4
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• pp.92-99
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• 2011

In order to protect the turbine blade from working fluid of high temperature, many cooling techniques such as internal convection cooling, film cooling, impinging jet cooling and thermal barrier coating have been developed. With all other things, film-cooling has been widely used as the important alternative. In the present work, numerical analysis has been performed to investigate and to compare the film-cooling performance of various film-cooling hole schemes such as cylindrical, crescent, louver, and dumbbell holes. To analyze the turbulent flow and the film-cooling mechanism, three-dimensional Reynolds-averaged Navier-Stokes analysis has been performed with shear stress transport turbulence model. The validation of numerical results has been assessed in comparison with experimental data. The characteristics of fluid flow and the film-cooling performance for each shaped hole have been investigated and evaluated in terms of centerline, laterally averaged and spatially averaged film-cooling effectivenesses. Among the film cooling holes, the dumbbell shaped hole shows better film-cooling effectiveness than the other shaped holes. And the louver and cylindrical shaped hole show the worst film cooling performance, and concentrated flows on near the centerline only.

• New & Renewable Energy
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• v.1 no.2 s.2
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• pp.41-52
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• 2005

The effects of internal manifold designs on the reactants feed-stream in Polymer Electrolyte Fuel Cells [PEFCs] is studied to figure out flow and thermal distribution patterns over an entire fuel cell stack. Reactants flows are modeled either laminar of turbulent depending on regions and the open channels in the bipolar plates are simulated by porous media where permeability should be pre-deter-mined for computational analysis. In this work, numerical models for reactants feed-stream In the PEFC manifolds are classified Into two major flow patterns: Z-shape and U-shape. Several types of manifold geometries are analyzed to find the optimal manifold configurations. The effect of heat generation in PEFC on the flow distribution is also Investigated applying a simplified heat transfer model in the stack level (i.e. multi-cell electrochemical power-generation unit). This modeling technique Is well suited for many large scale problems and this scheme can be used not only to account for the manifold flow pattern but also to obtain Information on the optimal design and operation of PEFC systems.

• Geomechanics and Engineering
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• v.8 no.6
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• pp.811-828
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• 2015

Proper modelling of the basal resistance terms is key in simulating the motion of fluidized granular flow. In this paper, standard depth-averaged governing equations of granular flow are used together with the classical Coulomb, Voellmy, and velocity dependent friction models (VDFM). A high-resolution modified TVDLF method is implemented to solve the partial differential equations without numerical oscillations. The effects of basal resistance terms on the motion of granular flows such as geometric shape evolution, travel times and final deposits are analyzed. Based on the numerical results, the predictions of the front and rear end positions and developing length of granular flow with Coulomb friction model show excellent agreements with experiment results reported by Hutter et al. (1995), and illustrate the validity of the numerical approach. For the Voellmy model, the higher value of turbulent coefficient than reality may obtain more reasonable predicted runout for the small-scale avalanche or granular flow. The energy exchange laws indicate that VDFM is different from the Coulomb and Voellmy models, although the flow characteristics of both three models fit the measurements and observations very well.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.3
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• pp.27-36
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• 2018

Effective pesticide applications are needed to assure the quality and economic competitiveness of fruit production and lower the risk of spray drift. Experimental studies have shown that better spray coverage and less driftability require an understanding of the transport of spray droplets within turbulent airflows in the orchard and the interaction between droplet dynamics and tree canopies. This study developed a computational fluid dynamics (CFD) model to predict pesticide flows in the orchard and spray drift discharged from an air-assisted orchard sprayer. The model represented the transport of spray droplets as well as droplets captured by tree canopies, which were modeled as a conical porous model and branched tree model. Validation of the CFD model was accomplished by comparing the CFD results with field measurements. Spray depositions inside tree canopies and at off-target locations were in good agreement with the measurements. The resulting data presented that 38.6%~42.3% of the sprayed droplets were delivered to the tree canopies while 13.6%~20.1% were drifted out of the orchard, part of them reached farther than 200 m from the orchard. The study demonstrates that CFD model can be used to evaluate spray application performance and spray drift potential.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.306-309
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• 2006

Passive control of the shock wave/turbulent boundary-layer interaction control utilizing slotted plates over a cavity has been carried out. Effect of various slot configurations on the characteristics of the interactions are tested. Pitot/wall surface pressure distributions and flow visualizations including Schlierens and interference fringe patterns over a thin oil-film have been obtained at the downstream of the shock interactions. It was found that the interaction control by a certain slot-configuration could lead a reduction of the total pressure loss through the shock wave, however, the boundary layer thickness became thicker as compared with the case of no control.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.182-186
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• 2011

Ejector-diffuser system has long been used in many diverse fields of engineering applications and it has advantages over other fluid machinery, because of no moving parts and structural simplicity. This system makes use of high-pressure primary stream to entrain the low-pressure secondary stream through pure shear actions between two streams. In general, the flow field in the ejector-diffuser system is highly complicated due to turbulent mixing, compressibility effects and sometimes flow unsteadiness. A fatal drawback of the ejector system is in its low efficiency. Many works have been done to improve the performance of the ejector system, but not yet satisfactory, compared with that of other fluid machinery. In the present study, a mixing guide vane was installed at the inlet of the secondary stream for the purpose of the performance improvement of the ejector system. A CFD method has been applied to simulate the supersonic flows inside the ejector-diffuser system. The present results obtained were validated with existing experimental data. The mixing guide vane effects are discussed in terms of the entrainment ratio, total pressure loss as well as pressure recovery.

• Journal of Ship and Ocean Technology
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• v.10 no.2
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• pp.1-10
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• 2006

Numerical analysis of viscous flow around twin-skeg hull forms was conducted according to the variations of distance between skegs and vertical skeg inclinations by using a hydrodynamic analysis system, WAVIS. Six twin-skeg hull forms were derived by combining three distances between skegs (16m, 20m, 24m) and four vertical skeg angles ($0^{\circ},\;10^{\circ},\;15^{\circ},\;20^{\circ}$). It is found that the better resistance performance can be obtained with larger vertical skeg angle and smaller skeg distance for the present test cases. It also can be seen that the same trend is true for the nominal wake distributions in the propeller plane. Those tendencies were confirmed by the experimental results of MOERI. It is shown that numerical analysis can be a useful and practical tool for the evaluation and improvement of hydrodynamic performances for the complex stern hull forms with twin skegs.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2
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• pp.5-15
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• 1995

An application of the cross correlation technique by adopting ultrasonic waves for water pipe flow measuring purpose is studied. It is a non-intrusive flow metering method by determining the time of the flight of the flow turbulent noise and its non-obstructing mechanism enables to reduce process energy loss due to the flowmeter obstruction. A digital signal processor for the purpose of the real time Fourier transform was employed for the fast time calculation of the flow velocity. The overall accuracy was found as about $1\%$ for flow velocities from 0.25 m/s up to 16 m/s and for the pipe inside diameters from 50mm to 248mm. The cross correlation technique can be used for the tap water utility including most common liquid flows.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.327-330
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• 2006

Numerical study on the passive control of the oblique shock wave/turbulent boundary-layer interaction control utilizing slotted plates over a cavity has been carried out. Numerical results have been compared with the experimental observations, such as pitot/wall surface pressures and Schlieren flow visualizations, obtained for the same boundary conditions. It was found that the present numerical results shows a good agreement with experimental data. Further, the effect of different slot configurations including various number, location and angle of slots on the characteristics of the interactions are also tested, focusing on the variation of the piot pressure and the boundary-layer characteristics downstream of the interaction and the recirculating mass flux through cavity.