• Clean Technology
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• v.27 no.1
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• pp.61-68
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• 2021

Selective catalytic reduction (SCR) is widely used as a method of removing nitrogen oxide in large-capacity thermal power generation systems. Uniform mixing of the injected ammonia and the inlet flue gas is very important to the performance of the denitrification reduction process in the catalyst bed. In the present study, a computational analysis technique was applied to the ammonia injection system design process of a denitrification facility. The applied model is the denitrification facility of an 800 MW class coal-fired power plant currently in operation. The flow field to be solved ranges from the inlet of the ammonia injection system to the end of the catalyst bed. The flow was analyzed in the two-dimensional domain assuming incompressible. The steady-state turbulent flow was solved with the commercial software named ANSYS-Fluent. The nozzle arrangement gap and injection flow rate in the ammonia injection system were chosen as the design parameters. A total of four (4) cases were simulated and compared. The root mean square of the NH3/NO molar ratio at the inlet of the catalyst layer was chosen as the optimization parameter and the design of the experiment was used as the base of the optimization algorithm. The case where the nozzle pitch and flow rate were adjusted at the same time was the best in terms of flow uniformity.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.17-25
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• 2020

In this study, three-dimensional fluid flow analyses have been performed in order to investigate the performance characteristics of a horizontal axis tidal turbine (HATT) by solving three-dimensional Reynolds-averaged Navier-Stokes equations utilizing the shear-stress-transport turbulence model. The computational domain for the flow analysis has been composed of hexahedral grids, and the grid dependency test has been carried out so as to determine the optimum grid size. Performance characteristics of the HATT have been investigated in consideration of the effects of hub nose geometry, inflow angle, and the tower. It has been found that the power output can be enhanced along with an increase of the ratio of the length to the diameter of the turbine nose, and the power of HATT has been reduced by approximately 10% when the primary fluid flow had an inflow angle of 15°. The power output of downstream HATT is found to be lower than that of the upstream HATT by about 1%.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.65-72
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• 2012

Numerical simulations were performed to study the stall characteristics of turboprop aircraft. Stall characteristics were qualitatively investigated using the computational results of various configurations based on the combinations of propeller and high lift device. For the analysis of stall characteristics, three-dimensional Navier-Stokes solver with Spalart-Allmaras turbulence model was used and the relative motion between propeller and wing was simulated using sliding mesh technique. For the cruise configurations, major flow separation was occurred at the fuselage/wing fairing and the separation was reduced under propeller slipstream condition. For the high lift device configuration without propeller, major flow separation was occurred at the outboard side of nacelle. With rotating propeller, early stall onset due to low relative velocity and high effective angle of attack was observed on the outboard wing section. Regarding rotating direction of propeller, inboard-down direction was preferred due to the stall delay effect of propeller slipstream.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.1
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• pp.63-78
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• 2009

This paper presents the development of dynamically combined Typhoon generated surge-tide-wave numerical model which is applicable to shallow water. The newly developed model is based on both POM (Princeton Ocean Model) for the surge and tide and WAM (WAve Model) for wind-generated waves, but is modified to be applicable to shallow water. In this paper which is the first paper of the two in a sequence, we verified the accuracy and numerical stability of the hydrodynamic part of the model which is responsible for the simulation of Typhoon generated surge and tide. In order to improve the accuracy and numerical stability of the combined model, we modified algorithms responsible for turbulent modeling as well as vertical velocity computation routine of POM. Verification of the model performance had been conducted by comparing numerical simulation results with analytic solutions as well as data obtained from field measurement. The modified POM is shown to be more accurate and numerically stable compare to the existing POM.

• Journal of the Korean Society of Safety
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• v.10 no.3
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• pp.120-129
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• 1995

Since the rate and completeness of combustion in direct injection engines were controlled by the characteristics of gas flow fields and sprays, an understanding of those was essential to the design of the direct injection engines. In this study the numerical simulations of swirl effects on the characteristics of gas flow fields and sprays were performed using the spray model that could predict the interactions between gas fields and spray droplets. The governing equations were discretized by the finite volume method and the modified k- e model which included the compressibility effects due to the compression/expansion of piston was used. The results of numerical calculation of the spray characteristics in the quiescent environment were compared with the experimental data. There were good agreements between the results of calculation and the experimental data, except in the early stages of spray. In the motoring condition, the results showed that a substantial air entrainment into the spray volume was emerged and hence the squish motion was relatively unimportant during fuel injection periods. As the swirl ratio increased, the evaporation rate was increased due to the wide dispersion of the spray droplets and the strong interaction between spray droplets and gas fields.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.21-29
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• 2002

In the present study, a passive control method, using a porous wall and cavity system, is applied to the shock wave/boundary layer interactions in transonic moist air flow. The two-dimensional, unsteady, compressible, Navier-Stokes equations, which are fully coupled with a droplet growth equation, are solved by the third-order MUSCL type TVD finite difference scheme. Baldwin-Lomax model is employed to close the governing equations. In order to investigate the effectiveness of the present control method, the total pressure loss of the flow and the time-dependent behaviour of shock motions are analyzed in detail. The computed results show that the present passive control method considerably reduces the total pressure losses due to the shock wave/boundary layer interaction in transonic moist air flow and suppresses the unsteady shock wave motions over the airfoil as well. It is also found that the location of the porous ventilation significantly affects the control effectiveness.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.4
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• pp.28-34
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• 2019

In this study, pin-fin arrays, which are widely used for cooling turbine blades, were studied. The vortex generator in pin-fin arrays is located in front of the circular tube. The cross-section of the vortex generator is NACA-9410. The purpose of this study is to analyze heat transfer performance and flow characteristics of pin-fin arrays. The position of vortex generator is changed with the vertical flow direction on the bottom wall. Pin-fin arrays were calculated with 6000, 10000 and 15000 Reynolds number. The commercial program ANSYS v18.0 CFX and the turbulence model $k-{\omega}$ SST were used. As a result, the heat transfer performance increased up to 5.8% and pressure loss increased less than 1%.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.142-150
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• 2003

Turbulent flows and related heat transfer in a square heated duct is investigated by a turbulence model and a large eddy simulation. The cooling channel of calorimeter is modeled to the square duct. The nonlinear k-ε-fμ model of Park et al. [3] is slightly modified and their explicit heat flux model is employed. The Reynolds number is varied in the range 4000≤Reｂ≤20000. The heat transfer is closely linked to the secondary flows which driven by the turbulent motion. Its magnitude is 1~3% of the mean streamwise velocity. The relation of Nu~Re0.8Pr0.34 is validated by comparing with the predicted Nu of k-ε-fμ model. Finally, the coherent structures and thermal fluctuations are scrutinized.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.7-12
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• 2016

This paper deals with a parametric study on cooling channel configurations to enhance the cooling effect. As a cooling effect has been increased, the exhaust gas by the plant from a manufacture is becoming deceased. To solve this problem, the design of a efficient cooling system is needed. In this paper, the cooling channel was analyzed to improve the cooling performance. The heat transfer rates depending on the number of baffle and the heiht of fin were obtained by using numerical simulation method. Three-dimensional Reynolds-averaged Naiver-Stokes equations were used to estimate flow and heat transfer in cooling channel, and the $k-{\varepsilon}$ model for turbulence closure was employed.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.343-349
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• 2011

A loosely coupling method is adopted to combine a computational fluid dynamics (CFD) solver and the comprehensive structural dynamics (CSD) code, CAMRAD II, in a systematic manner to correlate the airloads, vortex trajectories, blade motions, and structural loads of the HART I rotor in descending flight condition. A three-dimensional compressible Navier-Stokes solver, KFLOW, using chimera overlapped grids has been used to simulate unsteady flow phenomena over helicopter rotor blades. The number of grids used in the CFD computation is about 24 million for the isolated rotor and about 37.6 million for the rotor-fuselage configuration while keeping the background grid spacing identical as 10% blade chord length. The prediction of blade airloads is compared with the experimental data. The current method predicts reasonably well the BVI phenomena of blade airloads. The vortices generated from the fuselage have an influence on airloads in the 1st and 4th quadrants of rotor disk. It appeared that presence of the pylon cylinder resulted in complex turbulent flow field behind the hub center.