• International Journal of Aeronautical and Space Sciences
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• v.17 no.3
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• pp.324-331
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• 2016

The present study focuses on the characteristics of a supersonic jet flowing from a rectangular nozzle exit on a flat plate. Flow visualization techniques using schlieren and kerosene-lampblack tracing are utilized to investigate shock reflection structures and boundary-layer separations over a flat plate. Wall pressure measurements are also carried out to quantitatively analyze the flow structures. All observations are repeated for multiple jet flow boundary conditions by varying the flap length and nozzle pressure ratio. The experimental results show that the jet flow structures over the flat plate are highly three-dimensional with strong bleeding flows from the plate sides, and that they are sensitive to plate length and nozzle pressure ratio. A multi-component force measurement device is also utilized to observe the characteristics of the jet flow thrust vectoring over the plate. The maximum thrust deflection angle of the jet is about $8^{\circ}$, demonstrating the applicability of thrust vector control via a flat plate installed at the nozzle exit.

• Wind and Structures
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• v.17 no.5
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• pp.515-535
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• 2013

The present study aims to investigate characteristics of the flow structures around the Ahmed body by using both experimental and numerical methods. Therefore, 1/4 scale Ahmed body having $25^{\circ}$ slant angle was employed. The Reynolds number based on the body height, H and the free stream velocity, U was $Re_H=1.48{\times}10^4$. Investigations were conducted in two parts. In the first part of the study, Large Eddy Simulation (LES) method was used to resolve the flow structures around the Ahmed body, numerically. In the second part of the study the particle image velocimetry (PIV) technique was used to measure instantaneous velocity fields around the Ahmed body. Time-averaged and instantaneous velocity vectors maps, streamline topology and vorticity contours of the flow fields were presented and discussed in details. Comparison of the mean and turbulent quantities of the LES results and the PIV results with the results of Lienhart et al. (2000) at different locations over the slanted surface and in the wake region of the Ahmed body were also given. Flow features such as critical points and recirculation zones in the wake region downstream of the Ahmed body were well captured. The spectra of numerically and experimentally obtained stream-wise and vertical velocity fluctuations were presented and they show good consistency with the numerical result of Minguez et al. (2008).

• Journal of the Korean Society of Visualization
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• v.1 no.1
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• pp.28-33
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• 2003

This paper presents the visualization method in which 3-dimensional(3D) microchannel flow can be detected using a confocal scanning microscope. By soft-lithography, we fabricated various Bio-MEMS(Micro Electro-Mechanical System) devices such as a disposable microchip for a flow cytometer and a micro-mixer, which have 3D structures. Injecting aqueous fluorescent solution in the microfluidic devices, we measured the flow in a steady state by the confocal scanning microscope. At first, we explain the principle of the confocal scanning microscope. And then we show the results from 3D visualization of microscopic flow structures using the confocal scanning microscope.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.47-54
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• 2007

Simultaneous 3-D LDV measurements of the in-cylinder flows of three different engine setups were summarized for the quantification of the flow characteristics in each vertical or horizontal plane, and in entire cylinder volume. The ensemble averaged-velocity, tumble and swirl motions, and turbulent kinetic energy during the intake and compression strokes were examined from the measured velocity data (approximately 2,000 points for each engine setup). The better spatial resolution of the 3-D LDV allows measurements of the instantaneous flow structures, yielding more valuable information about the smaller flow structures and the cycle-to-cycle variation of these flow patterns. Tumble and swirl ratios, and turbulent kinetic energy were quantified as planar and volumetric quantities. The measurements and calculation results were animated for the visualization of the flow, and hence ease to analysis.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.79-80
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• 2003

This paper presents experimental results on stirring characteristics in a microchannel with structures changed. We fabricated a new chaotic micro mixer and made by a RP(Rapid Rrototyping) technology. Flow visualization for the stirring effect was performed by using pure orator in a reservoir and fluorescent dye in the other. Chaotic mixing was achieved by introducing periodic perturbation in the field of the microchannel flow by means of shaped structures. It was found that the stirring is enormously enhanced at larger bock-height.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.25-31
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• 2004

This paper describes a new vibration-suppression technique for flexible cantilevered structures by using a pipe containing an internal flow. The stability and dynamic response are analyzed based on the finite element method. The flutter limit and optimum stabilizing fluid velocity are determined in root locus diagrams. The impulse responses of the system are studied by the mode superposition method to observe the damping rate of the motion. The stabilizing effect of an internal flow is demonstrated by impulse responses of the structures with and without an material damping. It is found that the response of the pipe with flow of liquid has a larger effect of, stabilizing than that with flow of gas.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.824-830
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• 2003

The Power Flow Finite Element Method(PFFEM) offers very promising results in predicting the vibration responses of system structures, and the first PFFEM software, PFADS has been developed in Seoul National University for the vibration predictions and analysis of coupled system structures in medium-to-high frequency ranges. PFFEM is numerical method which solves energy governing equation using finite element technique for complicated structures where the exact solutions are not available. Through the upgrades, the current version PFADS R3 could cover the general beam and plate structures including various kinds of beam-plate rigid joints, spring-damper connection and rigid body connection within beam and plate in addition. This software is composed of three parts; translator, model converter and solver. The translator makes its own FE-model from bulk data of commercial FE software, and the model converter is used to convert FE-model to PFFE-model automatically. The solver calculates vibrational energy density and intensity for PFFE-model by solving global matrix equations of PFFEM. For the applications of PFADS R3, two vehicle models and a container model are examined with respect to major parameters, and reliable results are obtained.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.2
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• pp.82-88
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• 2004

To evaluate the tidal flow around the transmission type harbour structures, the numerical models considering hydraulic resistance are used. The traditional governing equations of depth-integratef hydrodynamics are modified by using of the drag force term. As a numerical model to evaluate the rate of tidal exchange, the Random-walk method is used. The models are applied in a design of the pile-supported pier structures in Busan harbour site, Korea, where the flow speed and the tidal exchange are more promotive than the case of non-transmission structure. The developed model will be applied usefully to design the transmission type structure in the ocean space.

• Journal of Ocean Engineering and Technology
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• v.36 no.6
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• pp.364-379
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• 2022

Coastal communities have been vulnerable to extreme coastal flooding induced by hurricanes and tsunamis. Many studies solely focused on the overland flow hydrodynamic and loading mechanisms on individual inland structures or buildings. Only a few studies have investigated the effects of flooding mitigation measures to protect the coastal communities represented through a complex series of building arrays. This study numerically examined the performance of flood-mitigation measures from tsunami-like wave-induced overland flows. A computational fluid dynamic model was utilized to investigate the performance of mitigation structures such as submerged breakwaters and seawalls in reducing resultant forces on a series of building arrays. This study considered the effects of incident wave heights and four geometrically structural factors: the freeboard, crest width of submerged breakwaters, and the height and location of seawalls. The results showed that prevention structures reduced inundation flow depths, velocities, and maximum forces in the inland environment. The results also indicated that increasing the seawall height or reducing the freeboard of a submerged breakwater significantly reduces the maximum horizontal forces, especially in the first row of buildings. However, installing a low-lying seawall closer to the building rows amplifies the maximum forces compared to the original seawall at the shoreline.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.352.2-352
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• 2002

In this paper, Power Flow Analysis (PFA) method has been applied to the prediction of vibration energy density and intensity of coupled shell structures in the medium-to-high frequency ranges. To consider the wave transformation at joint between shell elements, power transmission and reflection coefficients are investigated for various joint angles, and here Donnell-Mushtari thin shell theory has been used. (omitted)