• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 추계 학술대회논문집
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• pp.1-9
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• 2001

In this paper, some numerical methods recently developed for gas-liquid two-phase flows are reviewed. And then, a preconditioning method to solve cavitating flow by the author is introduced. This method employs a finite-difference Runge-Kutta method combined with MUSCL TVD scheme, and a homogeneous equilibrium cavitation model. So that it permits to treat simply the whole gas-liquid two-phase flow field including wave propagation, large density changes and incompressible flow characteristic at low Mach number. Finally, numerical results such as detailed observations of the unsteady cavity flows, a sheet cavitation break-off phenomena and some data related to performance characteristics of hydrofoils are shown.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1995년도 춘계학술발표회 초록집
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• pp.53-59
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• 1995

In a hot water extraction process, the flow pattern of upper region in a storage tank is a major reason of mixing between hot water and cold water. In this study, the temperature distribution in a storage tank was measured to predict the flow pattern of upper region, and the degree of stratification was analysed to the variables dominating a extraction process. And also, it was found that the degree of stratification improved expecially in a low flow rate in case of using modified distributor I(DMI) as a outlet port type.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1015-1022
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• 2003

Flows in a regenerative pump were calculated for several flow-rates, using the CFX-Tascflow. The calculated results show the vortex structure in the impeller and side channel. The predicted performance shows considerable discrepancy from the measured values for low flow rates. Main source of the difference is the leakage flow of pump strongly affecting the performance of pump. A simple correlation was proposed using calculated leakage flows through the simplified passage. One dimensional analysis were made for the recirculating flow and angular momentum transfer using calculated three dimensional data base.

• 한국유체기계학회 논문집
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• 제1권1호
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• pp.24-31
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• 1998

Aerodynamic performance tests and flow measurement were carried out for several radial impellers of NACA 65-810 airfoil. The data base obtained are to be used for verifying the methods of flow analysis and CFD codes. The effects of numbers and span of blades on the performances, efficiency and impeller exit flow are investigated in the present study. The flow rate on the performance curve is proportional to the span of the blade for the same value of fan pressure rise. The magnitude of radial velocity component at the impeller exit gradually decreases from the hub to shroud side. The magnitude of tangential velocity component gradually increases from the hub to shroud side. The way of variations of velocity is the same at the diffuser exit, however, becomes more uniform. The pressure rise performance increases with blade number at the small flow coefficients, however, decreases with the number of blade at the large flow coefficients. This shows that flow guidance in important at the low flow rate and the friction becomes significant at the high flow rate.

• 대한기계학회논문집B
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• 제29권9호
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• pp.971-978
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• 2005

Effects of inlet distorted flow on performance, stall and surge are experimentally investigated for a high-speed centrifugal compressor. Tested results for the distorted inlet flow cases are compared with the result of the undistorted one. The performance of compressor is slightly deteriorated due to the inlet distortion. The inlet distortion does not affect the number of stall cell and the propagation velocity. It also does not change stall inception flow rate. However, as the distortion increases, stall starts at the higher flow rate for low speed and at the lower flow rate for high speed. For 50,000 rpm stall occurrs as the flow rate decreases, however disappears fur the smaller flow rate. This is due to the interaction of surge and stall. After the stall and surge interact, the number of stall cell decreases.

• 한국항공운항학회지
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• 제12권3호
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• pp.13-24
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• 2004

It is easier to view flow visualization by using a water tunnel rather than a smoke wind tunnel because of low speed at same Reynolds number. Using a water tunnel also produces more definite flow visualization by the use of various color dyes. The flow uniformity in test section is very significant for accuracy of the test because most flow experiments elicit results through the installation of a model in uniform flow. The purpose of small-size desktop-type water tunnel is not to produce quantitative measurements, but rather to give a visualization of the fluid flow phenomenon. However, uniformity in the test section affects the accuracy of the results. Accordingly, this research estimates uniformity in a water tunnel test section by using the commercially available CFD code FLUENT. Results of the CFD analysis show that the flow uniformity of the test section is good.

• 한국전산유체공학회지
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• 제16권1호
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• pp.1-6
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• 2011

Flow instability is investigated in a two-dimensional channel with thin baffles placed symmetrically in the vertical direction and periodically in the streamwise dircetion. At low Reynolds numbers, the flow is steady and symmetric. Above a critical Reynolds number, the steady flow undergoes a Hopf bifurcation leading to unsteady periodic flow. As Reynolds number further increases, we observe the onset of secondary instability. At high Reynolds numbers, the two-dimensional periodic flow becomes three dimmensional. To identify the onset of secondary instability, we carry out Floquet stability analysis. We obseved the transition to 3D flow at a Reynolds number of about 125. Also, we computed dominant spanwise wavenumbers near the critical Reynolds number, and visualized vortical structures associated with the most unstable spanwise wave.

• International Journal of Aeronautical and Space Sciences
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• 제1권1호
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• pp.36-47
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• 2000

Three-dimensional compressible turbulent flow fields within the passage of a diffusing S-duct have been simulated by solving the Navier-Stokes equations with SIMPLE scheme. The average inlet Mach number is 0.6 and the Reynolds number based on the inlet diameter is $1.76{\times}10^6$ The extended $k-{\varepsilon}$ turbulence model is applied to modeling the Reynolds stresses. Computed results of the flow in a circular diffusing S-duct provide an understanding of the flow structure within a typical engine inlet system. These are compared with experimental wall static-pressure, total-pressure fields, and secondary velocity profiles. Additionally, boundary layer thickness, skin friction values, and streamlines in the symmetric plane are presented. The computed results depict the interaction between the low energy flow by the flow separation and the high energy flow by the reversed duct curvature. The computed results obtained using the extended $k-{\varepsilon}$ turbulence model.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1853-1859
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• 2001

An experimental study is presented for a flow field in a two dimensional wavy channels by PIV. This flow has two major applications such as a blood flow simulation and the enhancement of heat transfer in a heat exchanger. While the numerical flow visualization results have been limited to the fully developed cases, existing experimental results of this flow were simple qualitative ones by smoke or dye streak test. Therefore, the main purpose of this study is to produce quantitative flow data for fully developed and developing flow regimes by the Correlation Based Correction PIV (CBC PIV) and to conjecture the analogy between flow characteristics and heat transfer enhancement with low pumping power. Another purpose of this paper is to examine the onset position of the transition and the global mixing, which results in transfer enhancement. PIV results on the Fully developed and developing flow in a wavy channel at Re=500, 1000 and 2000 are obtained. for the case Reynolds Number equals 500, the PIV results are compared with the finite difference numerical solution.

• Journal of Magnetics
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• 제19권1호
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• pp.32-36
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• 2014

The purpose of this study was to investigate the effect of pulsed magnetic field (PMF) and low frequency low level laser (LFLLL) stimuli on acupoint LI4 (Hegu) using photoplethysmography (PPG). Our PMF system was designed to generate maximum intensity of 0.20 T at a transition time of 0.16 ms, with pulse intervals of 1 Hz. The diode laser with wavelength of 650 nm and power of 5 mW was also employed. It was observed the change of the pulsating blood volume through measuring PPG signals from both hands. These results imply that stimulating acupoint LI4 with PMF and LFLLL improves the circulation of peripheral vascular system. In particular, PMF stimulation brings a big improvement of the blood flow even with short term stimulation of 3-4 minutes compared to LFLLL stimulus.