• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.88-96
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• 2008

Effects of the duct inlet guide vane on the flowrate distribution characteristics of the defroster nozzle exit in a defrost duct system were investigated experimentally to design the optimum heating, ventilation and air conditioning (HVAC) system applied in an automotive compartment. A 3-dimensional hot-wire anemometer system was used to measure the velocity field in the vicinity of the defroster nozzle jet flow and the velocity distributions near the windshield interior surface. At first, two cases of with- and without-duct inlet guide vanes were considered as the test condition, and then three cases of the duct inlet guide vane were tested to determine the optimum guide vane shape and their positions. The arrangement of the duct inlet guide vanes has an effect on the improved flowrate distribution at the defroster nozzle exit and near the windshield interior surface. However, the application of the lots of guide vane to control the flow direction leads to increase the flow resistance, resulting in the decreased flowrate issuing from the defroster nozzle. The shape of the duct inlet guide vane affects not only the flowrate distribution between the driver side and the assistant driver side but also the reduction of the flow resistance in the defrost duct system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1416-1425
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• 1996

A numerical method has been proposed to predict 3-dimensional flow in a duct system with multiple outlets. For the duct system, it is supposed that the pressure values are given at multiple outlets while the velocity profile is given at a inlet. To maintain the continuity of pressure distribution between main and branch duct, present method allows that the pressure value taken from analysis of branch duct can be converted to the main duct analysis. The result from present method which can handle the pressure boundary condition closely coincided with that from regular method which can handle the velocity boundary condition only. Furthermore the flow distribution from present method showed good agreement with that from the single block method. From the comparison of the present method with the total pressure method used for engineering duct design, 13% of discrepancy in pressure loss was shown between the main duct inlet and the branch duct outlet.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.1
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• pp.33-39
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• 1999

In this paper an experimenatal investigation of characteristics of developing ransitional steady flows in a square-sectional $180^{\circ}$ curved duct is presented, The experimental study is carried out to measure axial velocity profiles secondary flow velocity profiles and entrance length by using Laser Dopper Velocimeter(LDV) system. The flow development is found to depend upon Dean number and curvature ratio. Of special interest is the secondary flow generated by centrifugal effects in the plane of the cross-section of the duct. The secondary flows becomes strong from $120^{\circ}$ of bended angle on the duct. The entrance length of transitional steady flow is obtained to $120^{\circ}$ of bended angle of the duct in this experimental conditions.

• The KSFM Journal of Fluid Machinery
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• v.19 no.1
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• pp.18-23
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• 2016

A HVAC(Heating Ventilation and Air Conditioning) is adapted to increase the comfort of the cabin environment for train. The train HVAC duct system has very long duct and many outlets due to the shape of a train set. the duct cross section shape is limited by a roof structure and equipments. Therefore, the pressure distribution and flow uniformity is an important performance indicator for the duct system. In this study, the existing blow down type HVAC duct system for a train was supplemented to improve the flow uniformity by applying a design method combining design of experiment (DOE) with numerical analysis. The design variables and the test sets were selected and the performance for each test set was evaluated using CFD(Computational Fluid Dynamics). The influence of each design variable on the system performance was analysed based on the results of the performance evaluation on the test sets. Furthermore, the optimized model, whose the flow uniformity was improved was produced using the direct optimization(gradient-based method). Finally, the performance of the optimized model was evaluated using numerical analysis, and it was confirmed that its flow uniformity has indeed improved.

• Journal of Biomedical Engineering Research
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• v.17 no.4
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• pp.515-524
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• 1996

The flow characteristics of developing unsteady laminar flow in a square-sectional $180^{\circ}$ curved duct are experimentally investigated by using laser doppler velocimerty (LDV) system with data acquisition and processing system of rotating machinery resolver(RMR) and PHASE software. The major flow characteristics of developing laminar pulsating flows are presented by mean velocity profilel velocity distribution of secondary flow, wall shear stress distributions, entrance lengths according to dimensionless angular frequency($\omega^+$), velocity amplitude ratio($A^1$), and time-averaged Dean number($De_ta$). The velocity profiles and wall shear stress distribution of laminar pulsating flow with dimensionlessangular frequency show the flow characteristics of the quasi-steady laminar flow in a curved duct. The developing region of laminar pulsatile flows in a square-sectional $180^{\circ}$ curved duct is extended to the curved duct angle of approximately $120^{\circ}$ under the present experimental condition.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1742-1747
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• 2003

When a shock wave is discharged from the exit of a duct, complicated flow is formed near the duct exit. The flow field is much more complicated under the ground effects or any other objects near the exit of a duct, such as the circumstance near the exit of the high-speed railway tunnel. The resulting flow is essentially three-dimensional unsteady with the effects of strong compressibility. In the current study, three-dimensional flow fields of the weak shock wave which is discharged from the exit of a duct are numerically investigated using a CFD method. Computations are performed for the weak shock wave in the range below 1.5. The results obtained show that the directivity and magnitude of the weak shock discharged strongly depend upon the Mach number of initial shock wave and are significantly influenced by the ground effects.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.579-587
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• 1999

The flow distribution characteristics in a complex duct system have been investigated in this paper by three means, namely experimental measurement, numerical simulation and the Extended T-method analysis. While the exit flow rates predicted by the three-dimensional CFD calculation and those given by the experiment show a close agreement, the results from the one-dimensional Extended T-method are found to differ from the experiment by -22.2% to 26.3% for the various exits. These discrepancies may be attributed to the underlying limitation concerning the fitting loss coefficients, which assume that the flow in front of the fittings is fully developed. It is proposed that, in order to analyse the three-dimensional flow distributions in a complex duct system by one-dimensional analysis such as the Extended T-method, further Improvements to the fitting loss coefficients should be made.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.59 no.1
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• pp.65-73
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• 2023

This study analyzed the duct characteristics of hubless rim-driven propeller (RDP) used in underwater robots. In the previous study, flow visualization experiments were performed with an advancing ratio of 0.2 to 1. The vortex at the front of the duct increased in strength while maintaining its size as the advancing ratio decreased. Therefore, it is necessary to study the optimization of the duct shape. Conventional propeller thrusters use acceleration/deceleration ducts to increase their efficiency. However, unlike conventional propellers, it is impossible to apply to airfoil acceleration/deceleration ducts due to the RDP structure. In this study, duct wake flow characteristics, thrust force, and efficiency according to the duct shape of RDP were analyzed using numerical analysis techniques. Duct design is limited and six duct shapes were designed. As a result, an optimized duct shape was designed considering duct wake flow characteristics, thrust force, and efficiency. The shape that the outlet width of the RDP was kept constant until the end of the duct showed higher thrust force and efficiency.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.05a
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• pp.127-133
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• 2000

In the present study flow characteristics of turbulent pulsating flow in a square-sectional 180。 curved duct are investigated experimentally. in order to measure axial velocity and secondary flow distributions experimental studies for air flow are conducted in a square-sectional $180^{\circ}$ curved duct by using the LDV system with the data acquisition and the processing system of the Rotating Machinery Resolver (RMR) and the PHASE software. The experiment is conducted on seven sections form the inlet(${\phi}=180^{\circ}$) at $30^{\circ}$ intervals of the duct. The results obtained from the experimentation are summarized as follows : In the axial velocity distributions of turbulent pulsating flow when the ratio of velocity amplitude(A1) is less than one there is hardly any velocity change in the section except near the wall and any change in axial velocity distribution along the phase. The secondary flow of turbulent pulsating flow has a positive value at the vend angle of $150^{\circ}$ without regard to the ratio of velocity amplitude. The dimensionless value of secondary flow becomes gradually weak and approaches zero in the region of bend angle $180^{\circ}$ without regard to the ratio of velocity amplitude.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.15-23
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• 2000

In the present study, flow characteristics of turbulent pulsating flow in the square-sectional $180^{\circ}$curved duct are investigated experimentally. In order to measure axial direction velocity and secondary flow distributions, experimental studies for air flow are conducted in the square-sectional $180^{\circ}$curved duct by using the LDV system with the data acquisition and the processing system of the Rotating Machinery Resolver (RMR) and the PHASE software. The experiment is conducted on seven sections form the inlet($\phi=0^{\circ}$) to the outlet($\phi=180^{\circ}$) at $30^{\circ}$intervals of the duct. The results obtained from the experimentation are summarized as follows : In the axial direction velocity distributions of turbulent pulsating flow, when the ratio of velocity amplitude (A1) is less than one, there is hardly any velocity change in the section except near the wall and in axial velocity distribution along the phase. The secondary flow of turbulent pulsating flow has a positive value at the bend angle of $150^{\circ}$regardless of the ratio of velocity amplitude. The dimensionless value of secondary flow becomes gradually weak and approaches zero in the region of bend angle $180^{\circ}$without regard to the ratio of velocity amplitude.