• 한국전산유체공학회:학술대회논문집
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• 2000.10a
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• pp.9-14
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• 2000

Computational methods can be classified roughly into two parts: one is the methods based on a potential flow theory, and the other is numerical solvers(CFD) based on Navier-Stockes equation. Methods based on a potential theory are more effective than CFD when the free surface effect is considered. Especially Rankine source method seems to become widespread for simulations of wave making problems. For computations of viscous flow problems, CFD techniques have rapidly been developed and have shown many successful results in the viscous flow calculation. Present paper introduces a computational system 'WAVIS' which includes a pre-processor, potential ant viscous flow solvers and a post-processor. To validate the system, the calculated results for modem commercial hull forms are compared with measurements. It is found that the results from the system are in good agreement with the experimental data, illustrating the accuracy of the numerical methods employed for WAVIS.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.1
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• pp.104-111
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• 2009

An unstructured overset mesh method has been developed for the simulation of unsteady flow fields around isolated rotors and rotor-fuselage configurations. The flow solver was parallelized for the efficient calculation of complicated flows requiring a large number of cells. A quasi-unsteady mesh adaptation technique was adopted to enhance the spatial accuracy of the solution and to better resolve the rotor wake. The method has been applied to calculate the flow fields around rotor-alone and rotor-fuselage configurations in forward flight. Validations were made by comparing the predicted results with those of measurements. It was demonstrated that the present method is efficient and robust for the prediction of unsteady time-accurate flow fields involving multiple bodies in relative motion.

• Journal of the Korean Society of Visualization
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• v.5 no.1
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• pp.43-48
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• 2007

Micro-PIV(particle image velocimetry) has been widely used to measure the velocity of micro flow. Although this micro-PIV method can give accurate 2D instantaneous velocity information of mea-surement plane, it cannot resolve the out of plane component of velocity vectors. Lots of the micro fluidic devices generate three-dimensional flow and 3D measurement of velocity is useful to understand the physics of micro flow phenomena. In this study, we constructed stereoscopic micro-PIV(SMPIV) system and applied this method to the impinging micro jet flow. The results show that this method can produce accu-rate 3D reconstruction of micro jet flow.

• Journal of the Korean housing association
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• v.17 no.2
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• pp.11-18
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• 2006

For the more comfortable thermal environment in residential buildings, it was necessary for variable components like as automatic flow limiting valves and/or balancing valves in hydronic system. And, these components had an effect on flow-rate and pressure inside pipe. In this case, the incompatibility between the design for the heating system and the selection of equipment was the causes of several problems in heating pipe network. In this study, we peformed measurements and analyses of flow rate and pressure inside pipe for radiant floor heating in residential buildings through field surveys and experiments in order to find out the actual conditions and problems. On the basis of this, we suggested the approach for the optimal flow-rate and pressure maintaining inside pipe in individual heating system.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.80-85
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• 2015

The unsteady-state, incompressible and three-dimensional large eddy simulation(LES) was carried out to analyze the structure of turbulent flow fields according to the operating loads of three-dimensional small-size axial fan(SSAF). LES shows the best prediction performance in comparison with any other Reynolds averaged Navier-Stokes(RANS) method because static pressure coefficients analysed by LES show a little bit larger than measurements including all flow coefficients. Also, it can be known that the wake of SSAF is divided into from axial flow to radial flow before and behind stall region according to the increase of static pressure through LES analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.9
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• pp.814-821
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• 2007

A hybrid method is presented for efficient computation of turbulent flow noise at low Mach numbers. In this method, the turbulent flow field is computed by incompressible large eddy simulation (LES), while the acoustic field is computed with the linearized perturbed compressible equations (LPCE) derived in this study. Since LPCE is computed on the rather coarse acoustic grid with the flow variables and source term obtained by the incompressible LES, the computational efficiency of calculation is greatly enhanced. Furthermore, LPCE suppress the instability of perturbed vortical mode and therefore secure consistent and stable acoustic solutions. The proposed LES/LPCE hybrid method is applied to three low Mach number turbulent flow noise problems: i) circular cylinder, ii) isolated flat plate, and iii) interaction between cylinder wake and airfoil. The computed results are closely compared with the experimental measurements.

• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.58-63
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• 2003

The performance of turbo pump drops rapidly and it gets into break-down when the void fraction reaches above the threshold value because the impeller flow passage is choked up with air bubbles. Phenomenological understanding of break-down and pumping recovery mechanisms under air-water two-phase flow conditions are therefore important for pump designers and essential assignment for researchers. In this paper, we investigated the characteristics of break-down and pumping recovery due to entrained air occurring inside a screw-type centrifugal pump which has a wide flow passage mainly through the findings of suction and discharge pressures, rotational speed, flow rate measurements and visualization.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.663-666
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• 2002

Hard disk drived (HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. The distribution of pressure disturbance on disks has relation to flow structure. To investigate the flow structure, time-resolved hot-wire measurements of the circumferential velocity component were obtained for the flow between the center pair of four disks of common radius $R_2$ coretating at angular velocity ${\Omega}$ in a fixed cylindrical enclosure. Hot-wire supporter acts as an obstruction in this case. The effects of rotating speed and size of hot-wire supporter diameter between disks on the flow driven by disks were investigated. Velocity spectra at the fixed space were measured to obtain the structure of inner and outer region in flow field.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.623-626
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• 2002

The object of present study is to find the flow characteristics of centrifugal turbomachinery according to the volute shape change. The experiments were carried out for two model; volute-A designed by free vortex conditions and volute-B designed for use in high mass flow rate conditions using the volute-A test results, Flow measurements were taken in shrouded impeller with 12 backward type blades by using a five-hole pilot-tube and carried out in 4 flow rate, $Q/Q_d\;=0,43,\;1.0,\;1.27,\;1,47$, respectively, For volute-B, we found that pressure distribution was more uniform at high flow rate and from $Q/Q_d\;:\;0,43\;to\;Q/Q_d\;:\;1,20$, losses decreased and efficiency increased compare with volute-A.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1892-1899
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• 2001

An experimental study was performed for measuring velocity and turbulence intensity in a circular tube for Re= 10,000, 15,000 and 20,000, with swirl and without swirling flow. The velocity fields were measured using PIV techniques and swirl motion was produced by a tangential inlet condition. Some preliminary measurements indicated that over the first 4 diameter, two regions of flow reversal were set up (the so called 2-cell structure). At the highest Reynolds numbers, the maximum values of the measured axial velocity components had moved toward the test tube wall and produce more flow reversal at the conter of the tube. As the Reynolds number increased, the turbulence intensity of swilling flow at the tube inlet also increased.