• Transactions of the Korean hydrogen and new energy society
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• v.29 no.4
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• pp.401-409
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• 2018

A numerical investigation has been conducted to find the effects of pressure losses by struts and rakes, and averaging methods on the performance of a multi-stage axial fan and a multi-stage axial compressor. Struts and rakes which produce pressure losses are installed upstream of the aerodynamic inlet plane in the fan and the compressor rigs. Some of normal stator vanes are substituted with thick vanes with total pressure probes to measure total pressure between stages. Three-dimensional Reynolds-averaged Navier- Stokes equations with $k-{\omega}$ SST turbulence model were applied to analyze the pressure losses by the struts, inlet rakes, and thick instrumented vanes. The hexahedral grids were used to construct computational domain. Inlet pressure losses were evaluated for the compressor as a function of Mach number. The passage pressure losses due to the instrumented vanes were evaluated at the two speed lines in the fan. Total properties, such as pressure and temperature, were evaluated at the exit of the fan and the compressor with two different averaging methods which are area-averaging and mass-averaging, respectively.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.25-35
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• 2012

An endwall boundary layer fence technique was adapted to improve the aerothermal environment of a gas turbine passage. The shape optimization of the fence was performed to maximize the improvement. The turbine passage was simulated by a $90^{\circ}$ turning duct (ReD=360,000). The main purpose of the present investigation was to focus on finding a endwall boundary layer fence with minimum total pressure loss in the passage and heat transfer coefficient on the endwall of the duct. Anothor objective function was to minimize the area on the endwall of the duct. An approximate optimization method was used for the investigation to secure the computational efficiency. Results indicated that a significant improvement in aerodynamic environment can be achieved through the application of the fence. Improvement of the thermal environment was smaller than that of the aerodynamic enviroment.

• Journal of Biosystems Engineering
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• v.13 no.3
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• pp.32-43
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• 1988

This study was attempted to investigate the pneumatic separation on separating unit of a combine harvester. The aerodynamic characteristics of threshed materials were analyzed by experiments. The air velocity distribution within the separation chamber was measured for various speeds of the winnower and suction fans to find out the operational and design conditions of the separating unit which would serve for reducing the grain loss from chaff outlet. The results of study arc summarized as follows: 1. Based on the separation curve of threshed materials analyzed, it was shown that three different kind. of materials-kernels, straw chaff, and leaf chaff were as a whole able to be separated pneumatically, regardless of varieties. However, a small amount of the separation grain loss may be expected to occur if the complete separation between kernels and straw chaff would be undertaken because some portion of their separation curve were overlapping. 2. The analysis of air velocity distribution showed that the separation chamber may be divided into two regions, the discharging and separating. The air velocity of the discharging region was 5-15 m/s and that of the separating region 2-5 m/s. 3. The air movement of the separation chamber may be a turbulence flow, being its speed became greater as it moves from the left to the right section of the separation chamber. The equi-speed line. of air flow had a steep gradient in between the discharging and the separation regions. The air velocity in the discharging region was much higher than the terminal velocity of kernels, because of which those kernels appearing in the region could be possibly exhausted as the grain loss from the chaff outlet. 4. The motion trajectory of threshed material in the separating region was dominantly affected by the winnower fan, on the other hand, its motion in the discharging region was affected by suction fan. 5. The grain loss from the chaff outlet was affected greatly by the winnower fan and the trace of kernel movement. It was observed that the optimum working speed to give minimum grain loss from chaff outlet for the combine tested should be maintained at 950~1,150 rpm for the winnower fan and 1,850 rpm for the suction fan. 6. It was shown that a large portion of grain loss from chaff outlet may occur when the kernels may bump against a portion of separation chamber wall and those kernels thus scattered into the discharging region were sucked by the suction fan. It was accordingly recommended that a new design of the wall of separation chamber so as to bump down kernels may be necessary to reduce grain loss from the chaff outlet.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.3
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• pp.23-29
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• 2010

A supersonic nozzle specially is one of the important part in a supersonic turbine usually adapted the impulse type, because the flow acceleration in the turbine theoretically is done only in the nozzle. The present study deals with numerical flow analysis to investigate the effect of nozzle shapes on the performance characteristics of a partial admission supersonic turbine. The flow analysis was performed for four different nozzle shapes. The shapes of the nozzles are circular, square, straight rectangular and bent rectangular nozzles. The results of the flow analysis showed that the aerodynamic loss of turbine is highly affected by the nozzle shapes, and the partial admission loss is also highly depended on nozzle shapes. Specially, bent rectangular nozzle had the best performance among the nozzle shapes

• Journal of the Korean earth science society
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• v.22 no.1
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• pp.40-46
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• 2001

Heat exchange between the atmosphere and sea is produced using the data from two 3m discus buoy installed by KMA in 1996. The meteorological and oceanic characteristics at the Dukjukdo and Chilbaldo buoy for the period 1996 ${\sim}$ 2000 are discussed. Daily averaged sensible heat and latent heat flux at each site are estimated from bulk aerodynamic method using given data and analyzed. Quantitative analyses show SST indicates 1-year cycle like air temperature but has 1 month lag. Sea level pressure is lowest in July, humidity is higher from May to August, and wind speed has averaged value of 5 m/s and higher in autumn and winter. Sensible heat flux analyses present that strong heat loss from the sea occurs in autumn and winter and weak heat loss from atmosphere appears in spring and summer, and net sensible heat loss from the sea is found throughout the year. The ocean significantly releases latent heat into atmosphere from August to May but get a little latent heat from atmosphere in other months. Net latent heat loss from the sea is larger than net sensible heat loss except in January and February. Comparison with two sites suggests that the magnitude of heat flux and their fluctuation are generally stronger at Dukjukdo than at Chilbaldo. In case study, both sensible and latent heat flux is a little more at Chilbaldo in March 1998, but substantially stronger at Dukjukdo in November 1996.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.53 no.1
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• pp.8-14
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• 2008

Ammonia ($NH_3$) volatilization from a silty clay loam paddy soil applied with non, straight urea, and coated urea, respectively, under transplanting in Milyang, Korea from 2002 and 2003 was simulated by a Water and Nitrogen Management Model (WNMM). Based on the data from the in-situ measurements, $NH_3$ volatilization during the rice growth was 6.04% and 1.46% of the applied nitrogen (N) from straight urea and coated urea, respectively. The bulk aerodynamic approach in WNMM satisfactorily predicted the difference in $NH_3$ loss during the given rice growing seasons from the two urea fertilizers. $R^2$ for the correlation between the predicted and observed NH3 loss during the calibration year (2002) was 0.53 less than 0.68 of the application year (2003). This difference could be due to the weather condition such as heavy rainfall and temperature during the calibration year.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.75-78
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• 2004

Various jet engines (Turbine engine family and RAM Jet engine) have been developed for high speed aircrafts. but their application to hypersonic flight is restricted by principle problems such as increase of total pressure loss and thermal stress. Therefore, the development of next generation propulsion system for hypersonic aircraft is a very important subject in the aerospace engineering field, SCRAM Jet engine based on a key technology, Supersonic Combustion. is supposed as the best choice for the hypersonic flight. Since Supersonic Combustion requires both rapid ignition and stable flame holding within supersonic air stream, much attention have to be given on the mixing state between air stream and fuel flow. However. the wider diffusion of fuel is expected with less total pressure loss in the supersonic air stream. So. in this study the direction of fuel injection is inclined 30 degree to downstream and the total pressure of jet is controlled for lower penetration height than thickness of boundary layer. Under these flow configuration both streams, fuel and supersonic air stream, would not mix enough. To spread fuel wider into supersonic air an aerodynamic force, baroclinic torque, is adopted. Baroclinic torque is generated by a spatial misalignment between pressure gradient (shock wave plane) and density gradient (mixing layer). A wedge is installed in downstream of injector orifice to induce an oblique shock. The schlieren optical visualization from side transparent wall and the total pressure measurement at exit cross section of combustor estimate how mixing is enhanced by the incidence of shock wave into supersonic boundary layer composed by fuel and air. In this study non-combustionable helium gas is injected with total pressure 0.66㎫ instead of flammable fuel to clarify mixing process. Mach number 1.8. total pressure O.5㎫, total temperature 288K are set up for supersonic air stream.

• The KSFM Journal of Fluid Machinery
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• v.11 no.5
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• pp.15-21
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• 2008

In modem wind power system of large capacity above 1MW, horizontal axis wind turbine(HAWT) is a common type. And, the optimum design of wind turbine to guarantee excellent power performance and its reliability in structure and longevity is a key technology in wind Industry. In this study, mathematical expressions based upon the conventional BEMT(blade element momentum theory) applying to basic 1MW wind turbine blade configuration design. Power coefficient and related flow parameters, such as Prandtl's tip loss coefficient, tangential and axial flow induction factors of the wind turbine analyzed systematically. X-FOIL was used to acquire lift and drag coefficients of the 2-D airfoils and we use Viterna-Corrigan formula to interpolate the aerodynamic characteristics in post-stall region. In order to predict the performance characteristics of the blade, a performance analysis carried out by BEMT method. As a results, axial and tangential flow factors, angle of attack, power coefficient investigated in this study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.4
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• pp.336-343
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• 2009

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses generated in the cascade of a turbine. Therefore, these are important part for improving a turbine efficiency. As well, many studies have been performed to decrease the secondary flow losses. The present study deals with the leading edge fences on a wing-body to decrease a horseshoe vortex, one of the factors to generate the secondary flow losses, and investigates the characteristics of the generated horseshoe vortex as the shape factors, such as the installed height, and length of the fence. The study was investigated using $FLUENT^{TM}$. Total pressure loss coefficient was improved about 4.0 % at the best case than the baseline.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.1
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• pp.23-28
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• 2012

In the present work, numerical analyses of air flow in HVAC duct have been carried out for enhancement of cooling/heating performance. For the analyses, three-dimensional Reynolds-averaged Navier-Stokes equations have been solved with the shear stress transport turbulence model. The numerical results were validated in comparison with the experimental data. Based on the numerical results, the HVAC duct was designed to reduce the pressure loss. The modified duct geometry shows largely reduced pressure drop in comparison with the reference geometry. And, through modified duct shape, the performance of air conditioning has been enhanced.