• 한국가시화정보학회지
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• 제14권2호
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• pp.12-17
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• 2016

In this work, we investigate the flow velocity controllability of a diffuser-type multiple hydrofoil duct by experimental and numerical flow visualization approaches. The flow velocity controllability is analyzed by changing the angle of the hydrofoil near the outlet, which is the diffuser, while the incoming flow velocity is 0.6 m/s in the experiment. When the diffuser angle is changed from 0 to 7.5 degree, the maximum velocity inside the duct is varied from 1.35 m/s to 1.52 m/s. Also, it is shown from the numerical analysis that the maximum velocity is varied from 1.09 m/s to 1.17 m/s in the same condition. Thus, the aspect of the acceleration in the duct due to the increase of the diffuser angle is similar between the both approaches. Therefore, the multiple hydrofoil duct can be used to control the flow speed inside the duct for continuously extracting power close to a rated capacity.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1683-1691
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• 2000

In this study, it is numerically revealed that the secondary flow due to the Coriolls force in a straight duct rotating about an axis perpendicular to that of the duct is analogous to that caused by the centrifugal force in a stationary curved duct. Dimensionless parameters $K_{LR}=Re/\sqrt{Ro}$ and Rossby number in a rotating straight duct were used as a set corresponding to Dean number and curvature ratio in a stationary curved duct. When the value of Rossby number and curvature ratio is large, it is shown that the flow field satisfies the `asymptotic invariance property`, that is, there are strong quantitative similarities between the two flows such as friction factors, flow patterns, and maximum axial velocity magnitudes for the same values of $K_{LR}$ and Dean number.

• 대한기계학회논문집
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• 제16권2호
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• pp.369-381
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• 1992

Characteristics of flow and heat transfer have been studied numerically in a square duct with a periodic pressure gradient. The flow in a duct was assumed to be fully developed and constant heat flux was imposed at the surfaces of a square duct. The distributions of axial velocity and time-space averaged temperature are investigated with angular velocity and amplitude ratio at a given Reynolds number 1000. When the periodic pressure gradient was imposed axially in a duct, the reverse flow may be occurred near the duct wall. The magnitude of this reverse flow increases as the amplitude ratio increases or as the angular frequency decreases. In the ranges of the amplitude ratio and the angular velocity in present investigation, the ratio of the periodic time space averaged temperature to the nonperiodic space averaged temperature has been found to be greater than one. This means that the cooling effect at the duct walls deteriorates with a periodic situation compared with nonperiodic one.

• International Journal of Advanced Culture Technology
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• 제10권3호
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• pp.295-306
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• 2022

The NOx removal performance of the SCR process depends on various factors such as catalytic factors (catalyst composition, shape, space velocity, etc.), temperature and flow rate distribution of the exhaust gas. Among them, the uniformity of the flow flowing into the catalyst bed plays the most important role. In this study, the flow characteristics in the SCR reactor in the design stage were simulated using a three-dimensional numerical analysis technique to confirm the uniformity of the airflow. Due to the limitation of the installation space, the shape of the inlet duct was compared with the two types of inlet duct shape because there were many curved sections of the inlet duct and the duct size margin was not large. The effect of inlet duct shape, guide vane or mixer installation, and venturi shape change on SCR reactor internal flow, airflow uniformity, and space utilization rate of ammonia concentration were studied. It was found that the uniformity of the airflow reaching the catalyst layer was greatly improved when an inlet duct with a shape that could suppress drift was applied and guide vanes were installed in the curved part of the inlet duct to properly distribute the process gas. In addition, the space utilization rate was greatly improved when the duct at the rear of the nozzle was applied as a venturi type rather than a mixer for uniform distribution of ammonia gas.

• 대한기계학회논문집B
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• 제29권5호
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• pp.545-553
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• 2005

In the present study, The characteristics of developing steady laminar flows of a straight duct connected to a $180^{\circ}$ curved duct were examined In the entrance region through experimental measurement. Flow characteristics such as shear stress distributions, pressure distributions and friction coefficient experimentally in a square cross-sectional straight duct by using the PIV system. For the PIV measurement by particles produced from mosquito coils particles. The experimental data were obtained at 9 points dividing the test sections by 400mm. Experimental results can be summarized as follows. Critical Reynolds number, $Re_{cr}$ which indicates transition from laminar steady flow to transition steady flow was 2,150. Shear stress per unit length on the wall was stronger than that in the fully developed flow region. This was attributed to the fact that shear stress and pressure loss in the curvature of a duct were increased. Pressure distributions were gradually decreased irrespective of Reynolds number In the whole test section. This trends were in a good agreement with the reference results. Pipe friction coefficient in the steady state flow region was calculate from method of least squares. The co-relationship between fiction coefficient and Reynolds number was established as follow; ${\lambda}=56/Re$.

• Advances in aircraft and spacecraft science
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• 제7권3호
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• pp.203-214
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• 2020

In many applications like the aircraft or the rockets/missiles, the flow from a nozzle needs to be expanded suddenly in an enlarged duct of larger diameter. The enlarged duct is provided after the nozzle to maximize the thrust created by the flow from the nozzle. When the fluid is suddenly expanded in an enlarged duct, the base pressure is generally lower than the atmospheric pressure, which results in base drag. The objective of this research work is to optimize the length to diameter (L/D) ratio of the enlarged duct using the CFD analysis in the flow field from the supersonic nozzle. The flow from the nozzle drained in an enlarged duct, the thrust, and the base pressure are studied. The Mach numbers for the study were 1.5, 2.0 and 2.5. The nozzle pressure ratios (NPR) of the study were 2, 5 and 8. The L/D ratios of the study were 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Based on the results, it is concluded that the L/D ratio should be increased to an optimum value to reattach the flow to an enlarged duct and to increase the thrust. The supersonic suddenly expanded flow field is wave dominant, and the results cannot be generalized. The optimized L/D ratios for various combinations of flow and geometrical parameters are given in the conclusion section.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.621-626
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• 2003

This paper is concerned with the numerical analyses of an S-shaped duct for the inter-channel between compressor spools. For the compactness and lightweight of an engine, the length of the S-shaped duct is desired to be minimized. Shortening the S-shaped duct however, flow separation is likely to occur. Numerical investigation using a three-dimensional Navier-Stokes flow solver has been performed to determine the availability of the minimization of an S-shaped duct. Computations are performed introducing the experimental data as the inlet flow condition of the OGV in determining the minimum length of the S-shaped duct. Also, the leaning effect of the OGV which assists the flow to turn radially inward are studied adopting mixing-plane method to consider the rotor/OGV interaction.

• 설비공학논문집
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• 제7권2호
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• pp.217-224
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• 1995

The effects of duct inlet conditions on fan characteristics and upper wind velocity fields were investigated for two kinds of impellers. As the duct inlet condition, the relative positions between duct inlet and fan impeller and the size of baffle plate mounted on a duct inlet were selected. The 3-dimensional velocity components in flow fields were measured by a 5-holes pitot tube. From the results of measurements, it was found that the size of baffle plate scarecely effect on upper wind flow fields and characteristics of fan. It was also confirmed that the upper wind velocity distributions can be estimated by the potential flow field with large baffle plate at duct inlet.

• 한국기계가공학회지
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• 제16권2호
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• pp.50-55
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• 2017

This study is about the distributions of flow in an air conditioning duct used for marine and oil drilling ships. Three-dimensional steady state turbulence was assumed as a governing equation for describing the flow in the air conditioning duct in this study. We compared the flow field with the pressure distribution according to the inlet velocity for two types of air conditioning duct, and stress and safe factors were simulated using ANSYS W/B. The result of fluid analysis showed an increased pressure drop in the duct according to the inlet velocity. Furthermore, secondary flow and complicated flow characteristics occurred at the bellows zone.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.157-159
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• 2008

An numerical investigation of the flow characteristics inside a diffusing S-duct inlet with and without vortex generators(VGs) was conducted. The primary discussion herein focuses on development of secondary flow in the S-duct with and without VGs, pressure recovery and distortion at the exit are also discussed. Full three-dimensional Navier-Stokes equations are solved using finite volume method and $k-\varepsilon$ turbulence model is employed. In order to validate the credibility of the numerical methods, predicted results of surface pressure are compared with flight test for the S-duct inlet without VGs, and it shows fairly good agreement. The result shows that VGs alter the flow characteristics in the S-duct and are effective in reducing distortion and ineffective in improving pressure recovery.