• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.9
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• pp.700-707
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• 2013

Experimental analyses on a supersonic plasma wind tunnel of CBNU (Chonbuk National University) were carried out. In these experiments, a segmented arc heater was employed as a plasma source and operated at the gas flow rates of 16.3 g/s and the total currents of 300 A. The input power reached ~350 kW with the torch efficiency of 51.4 %, which is defined as the ratio of total exit enthalpy to the input power. The pressure of plasma gas in the arc heater was measured up to 4 bar while it was down to ~45 mbar in a vacuum chamber through a Laval nozzle. During this conversion process, the generated supersonic plasma was expected to have a total enthalpy of ~11 MJ/kg from the measured input power and torch efficiency. In addition to the measurement of total enthalpy, a cone type probe was inserted into the supersonic plasma flow in order to estimate the angle between shock layer and surface of the probe. From these measurements, the temperature and the Mach number of the supersonic plasma were predicted as ~2,950 K and ~3.7, respectively.

• Wind and Structures
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• v.32 no.4
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• pp.371-391
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• 2021

Tornadoes are the most devastating meteorological natural hazards. Many empirical and theoretical numerical models of tornado vortex have been proposed, because it is difficult to carry out direct measurements of tornado velocity components. However, most of existing numerical models fail to explain the physical structure of tornado vortices. The present paper proposes a new empirical numerical model for a tornado vortex, and its load effects on a low-rise and a tall building are calculated and compared with those for existing numerical models. The velocity components of the proposed model show clear variations with radius and height, showing good agreement with the results of field measurements, wind tunnel experiments and computational fluid dynamics. Normal stresses in the columns of a low-rise building obtained from the proposed model show intermediate values when compared with those obtained from existing numerical models. Local forces on a tall building show clear variation with height and the largest local forces show similar values to most existing numerical models. Local forces increase with increasing turbulence intensity and are found to depend mainly on reference velocity Uref and moving velocity Umov. However, they collapse to one curve for the same normalized velocity Uref / Umov. The effects of reference radius and reference height are found to be small. Resultant fluctuating force of generalized forces obtained from the modified Rankine model is considered to be larger than those obtained from the proposed model. Fluctuating force increases as the integral length scale increases for the modified Rankine model, while they remain almost constant regardless of the integral length scale for the proposed model.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.19-19
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• 2009

Dynamic Stall is a flow phenomenon which occurs on the retreating side of helicopter rotor blades during forward flight. It also occurs on blades of stall regulated wind turbines under yawing conditions as well as during gust loads. Time scales occurring during this process are comparable on both helicopter and wind turbine blades. Dynamic Stall limits the speed of the helicopter and its manoeuvrability and limits the amount of power production of wind turbines. Extensive numerical as well as experimental investigations have been carried out recently to get detailed insight into the very complex flow structures of the Dynamic Stall process. Numerical codes have to be based on the full equations, i.e. the Navier-Stokes equations to cover the scope of the problems involved: Time dependent flow, unsteady flow separation, vortex development and shedding, compressibility effects, turbulence, transition and 3D-effects, etc. have to be taken into account. In addition to the numerical treatment of the Dynamic Stall problem suitable wind tunnel experiments are inevitable. Comparisons of experimental data with calculated results show us the state of the art and validity of the CFD-codes and the necessity to further improve calculation procedures. In the present paper the phenomenon of Dynamic Stall will be discussed first. This discussion is followed by comparisons of some recently obtained experimental and numerical results for an oscillating helicopter airfoil under Dynamic Stall conditions. From the knowledge base of the Dynamic Stall Problems, the next step can be envisaged: to control Dynamic Stall. The present discussion will address two different Dynamic Stall control methodologies: the Nose-Droop concept and the application of Leading Edge Vortex Generators (LEVoG's) as examples of active and passive control devices. It will be shown that experimental results are available but CFD-data are only of limited comparison. A lot of future work has to be done in CFD-code development to fill this gap. Here mainly 3D-effects as well as improvements of both turbulence and transition modelling are of major concern.

• Journal of Korea Water Resources Association
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• v.56 no.2
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• pp.125-137
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• 2023

In marine environments, plastics have become more abundant due to increasing plastic use. Especially, in coastal regions, particles may remain for a long time, and they interact with flows, wind, sand and human activities. This study aimed thus to observe how plastic debris interacts with and escape from sediments. A series of experiments were conducted in order to gain a better understanding of particle release from coastal sediments into water body. An oscillating water tunnel was built for the experiments, and used to generate oscillatory flows of relatively high Reynolds number and induce sediment transport. Spherical plastic particles of three different sizes was used in lieu of plastic debris in environments. It was observed that release of the particles was directly related to change of bedform, which is in turn determined by the flow condition. Also smaller particles tend to escape the sediment more readily. Critical values for dimensionless parameters are proposed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.387-392
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• 2006

A small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade. Experiments are performed to find flow characteristics of supersonic turbine with the cascade positions and to find factor of expansion loss. The supersonic cascade with a 2-dimensional supersonic nozzle was tested with the cascade positions. Firstly, the flow was visualized by Z-type Schlieren system. Finally, highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions, flow characteristics of the supersonic turbine were observed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.637-640
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• 2008

Noise generated from maglev vehicles mainly consists of two components, one is due to mechanical noise and the other due to aerodynamic noise. The former is due to the vehicle-guideway interactions and the latter results from the unsteady air flow around the vehicle. Aerodynamic noise could become more predominant around 225 km/h for maglev vehicles. In this paper, the aerodynamic noise of maglev vehicles is investigated experimentally. The results of the wind tunnel experiments of maglev vehicle models are introduced and compared. The comparison shows that the position of the main noise is between the bottom of the vehicle model and the rail. It is also found that the emitted sound pressure level is related to the gap size between the vehicle bottom and the rail.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1153-1158
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• 2009

The performance of louver-finned flat-tube and fin & tube radiators for computer CPU liquid cooling were experimentally investigated. In this study, 7 samples of radiators with different shape and pass number (1, 2, 10) were tested in a wind tunnel. The experiments were conducted under the different air velocity range from 1 to 4 m/s. The water flow rate through a pass was 1.2 LPM. Inlet temperatures of air and water were $20^{\circ}C$ and $30^{\circ}C$ respectively. It was found that the best performance was observed in the louver-finned flat-tube sample considering pressure drop and heat transfer coefficient.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.408-413
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• 2003

Naphthalene sublimation technique is used to investigate the average and local heat transfer from the circular rod, and to determine the average and local heat transfer from the circular rod with and without square wing type mixing vane in axial flow. The experiments are performed for a circular rod and flat plate with and without mixing vane in wind tunnel. In comparison with flat plate and circular rod in axial flow, averaged Nusselts number is increased 2 times as the increase of Reynolds number with mixing vane. Longitudinal vortex induced by square wing type has the stronger vortex strength, so square wing type vortex generator shows an effect further in downstream.

• Korean Journal of Computational Design and Engineering
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• v.2 no.2
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• pp.85-92
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• 1997

An axial flow fan design system has been made by integrating the self-developed programs and I-DEAS. By using the system, an axial flow fan was designed, manufactured and verified through the wind tunnel experiments in coorperation with a refrigerator appliance division. It has been shown that the optimal design without the ambiguity of the design parameters can be possible by the three-dimensional flow simulations using a self-developed CID code, FANS-3D. (Flow Analysis code using Navier Stokes aguations in Three-Dimensional curvilinear coordinates). By virtue of the fluency of the data flow, an optimally designed fan which satisfies design conditions can be selected in a short time and less cost. The manufacturing processes of a Mock-up and an injection molding die have been automated through the self-made interface programs which connnect from the start to the end. It has been shown that the newly developed fan by this system has a superior performance characteristics to an existing fan.

• International Journal of Control, Automation, and Systems
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• v.2 no.4
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• pp.494-500
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• 2004

The wing rock phenomenon is a high angle of attack aerodynamic motion manifested by limit cycle roll oscillations. Experimental studies reveal that direct control and manipulation of leading edge vortices, through the use of 'blowing' techniques is effective in the suppression of wing rock. This paper presents the design of a robust controller for the experimental implementation of one such 'blowing' technique - recessed angle spanwise blowing (RASB), to achieve wing rock suppression over a range of operating conditions. The robust controller employs Takagi - Sugeno fuzzy system, which is fine-tuned by experimental simulations. Performance of the controller is assessed by real-time wind tunnel experiments with an 80 degree swept back delta wing. Robustness is demonstrated by the suppression of wing rock at a range of angles of attack and free stream velocities. Numerical simulation results are used to further substantiate the experimental findings.