• International Journal of Fluid Machinery and Systems
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• v.2 no.2
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• pp.147-155
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• 2009

Dynamic characteristics of the clearance flow between an axially oscillating rotational disk and a stationary disk were examined by experiments and computations based on a bulk flow model. In the case without pressure fluctuations at the inlet and outlet of the clearance, parallel and contracting flow paths had an effect to stabilize the axial oscillation of the rotating disk. The enlarged flow path had an effect to destabilize the axial oscillation due to the negative damping and stiffness for outward and inward flows, respectively. It was shown that the fluid force can be decomposed into the component caused by the inlet or outlet pressure fluctuation without the axial oscillation and that due to the axial oscillation without the inlet or outlet pressure fluctuation. A method to predict the stiffness and damping coefficients is proposed for general cases when the device is combined with an arbitrary flow system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.69-74
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• 2004

In scramjet engines with sidewall compression inlet, it is well known that a non-uniform flow appears since a separated region is generated near the flow centerline on the body side. The separated region is caused by shock-boundary layer interaction and likely to cause un-start phenomena since the flow in the separated region is subsonic and acts as a communication path between the isolator and the combustor. In the present study, the non-uniform flow characteristics in the scramjet inlet-isolator region are numerically studied in detail. Effect of flow suction from body sidewall surface on the non-uniform flow field numerically examined to clarify the flow mechanism to suppress the un-start transition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1043-1048
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• 2003

An experimental investigation was executed to determine the capacity degradation due to non-uniform refrigerant distribution in a multi-path evaporator. In addition, the possibility of recovering the capacity reduction by controlling the refrigerant distribution among refrigerant paths was assessed. The finned-tube evaporator, which had a three-path and three-depth-row, was tested by controlling inlet quality, exit pressure, and exit superheat for each refrigerant path. The capacity reduction due to superheat unbalance between each path was as much as 30%, even when the overall evaporator superheat was kept at a target value of 5.6$^{\circ}C$. It may indicate that the internal heat transfer within the evaporator assembly caused the partial capacity drop. For the evaporator having air mal-distributions, the maximum capacity reduction was found to be 8.7%. A 4.5% capacity recovery was obtained by controlling refrigerant distribution to obtain the target superheat at the outlet of each path.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.3
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• pp.245-253
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• 2011

We investigate the flow characteristics of elementary-flow paths with $90^{\circ}$ bends; a velocity-control trim consists of such paths. For geometric similarity, the width and length of each path are selected, and the number of bends is 0, 4, or 8. The flow tests are conducted with the same flow-path elements. The numerical results are in good agreement with the experimental data. In elements without bends, the volume flow rate decreases with the length of the flow path, with a constant pressure drop between the inlet and the outlet. However, in flow paths with $90^{\circ}$ bends, it increases and then decreases with the length of the flow path. For a fixed number of $90^{\circ}$ bends, better pressure-drop characteristics are observed as the length of the flow path increases. For a fixed flow-path length, a flow-path element with more bends has a smoother pressure drop along the path.

• Journal of the korean Society of Automotive Engineers
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• v.7 no.1
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• pp.24-34
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• 1985

The study of unsteady gas exchange processes in the inlet and exhaust systems of the single-cylinder 4-stroke cycle spark ignition engine is presented in this paper. The generalized method of characteristics including friction, heat transfer, change of flow area and entropy gradients was used for solving the equations defining the gas exchange process. The path line calculation was also conducted to allow for calculation of the gas composition and entropy change along the path lines, and of the variable specific heat due to the change of temperature and composition. As the result of the simulation, the properties at each point in the inlet and exhaust pipe, pressure and temperature in the cylinder, and charging efficiency were obtained. Pumping loss and residual gas fraction were also computed. The effect of engine speed, exhaust and inlet pipe length on the pumping loss and charging efficiency were studied showing that the results were in agreement with what has been known from experiments.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.44-50
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• 2001

A numerical study was made to choose the better turbulence model for the flow in the discharge flow path from a diffuser to a wall. In this study standard $\kappa-\epsilon$ model(SKE), RNG $\kappa-\epsilon$ model(RNG), and Reynolds stress model(RSM) were applied. In case of the flow with relatively high Reynolds number at a diffuser inlet, the pressure loss coefficients by RNG have a tendency to be near to those by SKE at small ratio(below about 0.35) of $h/D_o$, but to those by RSM at large ratio(above about 0.35). At large ratio RNG begins to enlarge the effects of rapid strain and streamline curvature. RNG & RSM are recommended as the appropriate turbulence models for this case. But it is noticeable that the velocity gradient pattern in RNG is same as in SKE, and also that the total pressure distribution in RNG is same as in RSM only at swirling flow area, same as in SKE only at main flow area.

• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.735-744
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• 2012

In order to quantify the flow distribution characteristics of APR+ reactor, a test was performed on a test facility, ACOP ($\underline{A}$PR+ $\underline{C}$ore Flow & $\underline{P}$ressure Test Facility), having a length scale of 1/5 referring to the prototype plant. The major parameters are core inlet flow and outlet pressure distribution and sectional pressure drops along the major flow path inside reactor vessel. To preserve the flow characteristics of prototype plant, the test facility was designed based on a preservation of major flow path geometry. An Euler number is considered as primary dimensionless parameter, which is conserved with a 1/40.9 of Reynolds number scaling ratio. ACOP simplifies each fuel assembly into a hydraulic simulator having the same axial flow resistance and lateral cross flow characteristics. In order to supply boundary condition to estimate thermal margins of the reactor, the distribution of inlet core flow and core exit pressure were measured in each of 257 fuel assembly simulators. In total, 584 points of static pressure and differential pressures were measured with a limited number of differential pressure transmitters by developing a sequential operation system of valves. In the current study, reactor flow characteristics under the balanced four-cold leg flow conditions at each of the cold legs were quantified, which is a part of the test matrix composing the APR+ flow distribution test program. The final identification of the reactor flow distribution was obtained by ensemble averaging 15 independent test data. The details of the design of the test facility, experiment, and data analysis are included in the current paper.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.771-776
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• 2001

By matching a well established fast throughflow code, with standard loss correlations, and an efficient optimization algorithm, a new design system has been developed, which optimizes inlet and exit flow-field parameters for each blade row of a multistage axial flow turbine. The compressible steady state inviscid throughflow code based on streamline curvature method is suitable for fast and accurate flow calculation and performance prediction of a multistage axial flow turbine. A general purpose hybrid constrained optimization package, iSIGHT has been used, which includes the following modules: genetic algorithm, simulated annealing, modified method of feasible directions. The design system has been demonstrated using an example of a 5-stage low pressure steam turbine for 800MW thermal power plant previously designed by HANJUNG. The comparison of computed performance of initial and optimized design shows significant improvement in the turbine efficiency.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.517-522
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• 2001

The exit edges of a diffuser are smoothly rounded, and a wall is located perpendicularly to a diffuser exit. The fluid is discharged towards the radial direction of a diffuser after impinging against a wall from a diffuser. In this flow path, pressure loss coefficients have been calculated by the variables of Reynolds number at a diffuser inlet, distance between a diffuser exit and a wall, and turbulence models. As a result, it was calculated that $h/D_0$ ratio between $0.35\sim0.4$ has the minimum pressure loss coefficient regardless of Reynolds number and turbulence models. It was also found that in case of the flow with relatively high Reynolds number at a diffuser inlet, the pressure loss coefficients by RNG $k-\varepsilon$ model have a tendency to be near to those by standard $k-\varepsilon$ model at small ratio of $h/D_0$, but to those by RSM at large ratio.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.470-476
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• 2019

The braking force for a train is generally provided by compressed air. The pressure valve system that is used to apply appropriate braking forces to trains has a complex flow circuit. It is possible to make a channel shape that can increase the flow efficiency by 3D printing. There are restrictions on the flow shape design when using general machining. Therefore, in this study, the compressed air flow was analyzed in a pressure valve system by comparing flow paths made with conventional manufacturing methods and 3D printing. An analysis was done to examine the curvature magnitude of the flow path, the diameter of the flow path, the magnitude of the inlet and reservoir pressure, and the initial temperature of the compressed air when the flow direction changes. The minimization of pressure loss and the uniformity of the flow characteristics influenced the braking efficiency. The curvilinear flow path made through 3D printing was advantageous for improving the braking efficiency compared to the rectangular shape manufactured by general machining.