• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.109-112
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• 2004

Of late, the thrust vectoring control, using fluidic co-flow and counter-flow concepts, has been received much attention since it not only improves the maneuverability of propulsive engine but also reduces an additional material load due to the trailing control wings, which in turn reduce the aerodynamic drag. However, the control effects are not understood well since the flow field involves very complicated non: physics such as shock wave/boundary layer interaction, separation and significant unsteadiness. Existing data are not enough to achieve the effectiveness and usefulness of the thrust vectoring control, and systematic work is required for the purpose of practical applications In the present study, computational study has been performed to investigate the effects of the thrust vector control using the fluidic co-and counter-flow concepts. The results obtained show that, for a given pressure ratio, the thrust deflection angle has a maximum value at a certain suction flow rate, which is at less than $5\%$ of the mass flow rate of the primary jet. With a longer collar, the same vector angle is achievable with smaller mass flow rate.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.2
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• pp.30-37
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• 2006

The purpose of this study is to visualize the characteristics of ER fluids as preceding step of developing 3 port ER valves. ER fluids are made with silicone oil and 3 weight fraction starch having hydrous particles. The flow visualization of ER fluids flow is obtained by CCD camera with changing the strength of electric field to ER fluids flow. As the strength of the electric field increases, more clusters in flow are made and these clusters are though to be the reasons of the load flow rate being increased and the outlet flow rate being decreased. The ER Valves and load and outlet flow rate check method are considered to be applied to the fluid power control system.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.3
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• pp.465-471
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• 2013

Flow rate control is the uppermost concern for a trochoid hydraulic pump. Cavitation within the flow field of the pump has the greatest effect on the flow control during high-speed pump rotation of approximately 3500~4000 RPM. In this paper, based on AMESim$^{(R)}$ and Solid Works$^{(R)}$, we will present a method to simulate cavitation by analyzing the control factors of a trochoid pump, including the hydraulic pressure change at the outlet, flow rate based on the rotation speed of the inner rotor, leakage through the gap between the outer and inner rotors, and discharging angle of the outlet. The proposed methodology of the [cavitation simulation will enable field engineers to more easily design trochoid pumps, and will allow more concrete control over the flow rate of the pump by realizing an analysis model similar to the actual product model.

• Journal of Drive and Control
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• v.16 no.4
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• pp.32-37
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• 2019

Glove valves are used for various purposes in the process control field because such valves enable easy control of temperature and pressure. However, such valves are associated with significant loss of pressure and also have the disadvantage of complicating the shape of the cage or plug to facilitate linear flow rate change. In this paper, the shape of the plug, one of the valve flow control elements, was designed to improve the flow characteristics of the glove valve, and then CFD analysis was performed using compressible fluid. The numerical analysis results of the glove valve were analyzed according to the opening ratio and the pressure ratio of the valve. From these results, it was found that the proper notch on the side of the plug contributed to reducing the energy loss of the fluid through the valve and improving the linearity of the valve.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.648-654
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• 2011

The feed-water piping system constitutes a complex flow impedance network incorporating dynamic transfer characteristics which will amplify some pulsation frequencies. Understanding pressure pulsation waves for the feed-water recirculation piping system with cavitation problem of flow control valve is very important to prevent acoustic resonance. Feed water recirculation piping system is excited by potential sources of the shock pulse waves by cavitation of flow control valve. The pulsation becomes the source of structural vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation affects the reliability of the plant piping system. This paper discusses the piping vibration due to the effect of shock pulsation by the cavitation of the flow control valves for the recirculation piping of feed-water pump system in combined cycle power plants.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.12
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• pp.572-578
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• 2014

Heating energy was measured in an apartment housing unit with a district heating system, varying the kind of hot water distributors. Ondol coils passing through a living room raised the temperature of the room where the heating was turned off. Including this characteristic of Ondol heating into the modeling, we performed simulations and showed a verification by comparison with the results of measurements. As a result, a main flow control method, which changes hot water flow rate supplied to a housing unit according to the thermal load, can reduce the supplied flow rate and lower the return temperature, compared with a constant flow method. That can result in decreased heat loss in utility-pipe conduits even though the heating energy supplied is almost the same. An outdoor reset control that raises the temperature of the supplied hot water if the outdoor temperature falls has the effect of a quicker response in heating than the reduced flow rate and return temperature.

• Wind and Structures
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• v.34 no.4
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• pp.385-394
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• 2022

Global Warming has been driven majorly by the consumption of fossil fuels. Harnessing energy from wind is viable solution towards reducing carbon footprint created due to burning such fuels, However, wind turbines have their problems of flow separation and aerodynamic stall to tackle with. In an attempt to delay the stall angle and improve the aerodynamic characteristics of the NACA 0015 symmetrical aerofoil, lateral cylindrical ridges were attached to its suction surface, at chord positions ranging from 0.1c to 0.5c. The characteristics of the original and ridged aerofoils were obtained using simultaneous pressure readings taken in a wind tunnel, at a free stream Reynolds number of R_e = 2.81 × 10⁵ for a wide range of free stream angles of attack ranging from -45° to 45°. Depending on the ridge size, a delay in stall angle varying from 5° to 20° was achieved together with the maximum increase in lift in the post-stall phases. Additionally, efforts were made to identify the optimum position for each ridge.

• Journal of KSNVE
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• v.6 no.5
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• pp.607-616
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• 1996

A combined computational fluid dynamics(CFD)-Kirchhoff method is presented for predicting high-speed impulsive noise generated by a hovering blade. Two types of Kirchhoff integral formula are used; one for the classical linear Kirchhoff formulation and the other for the nonlinear Kirchhoff formulation. An Euler finite difference solver is solved first to obtain the flow field close to the blade, and then this flow field is used as an input to a Kirchhoff formulation to predict the acoustic far-field. These formulas are used at Mach numbers of 0.90 and 0.95 to investigate the effectiveness of the linear and nonlinear Kirchhoff formulas for delocalized flow. During these calculiations, the retarded time equation is also carefully examined, in particular, for the cases of the control surface located outside of the sonic cylinder, where multiple roots are obtained. Predicted results of acoustic far-field pressure with the linear Kirchhoff formulation agree well with experimental data when the control surface is at the certain location(R=1.46), but the correlation is getting worse before or after this specific location of the control surface due to the delocalized nonlinear aerodynamic flow field. Calculations based on the nonlinear Kirchhoff equation using a linear sonic cylinder as a control surface show a reasonable agreement with experimental data in negative amplitudes for both tip Mach numbers of 0.90 and 0.95, except some computational integration problems over a shock. This concliudes that a nonlinear formulation is necessary if the control surface is close to the blade and the flow is delocalized.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.2
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• pp.139-148
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• 2016

The passive control methods such as horizontal and vertical fences on the lower surface of the bluff body were applied to suppress the vortex shedding and enhance the aerodynamic stability of flow. For investigating the effects of the passive control methods, wind tunnel experiments on the unsteady flow field around a bluff body near a moving ground were performed. The boundary layer and velocity profiles were measured by the Hot Wire Anemometer (HWA) system and the vortex shedding patterns and flow structures in a wake region were visualized via the Particle Image Velocimetry (PIV) system. Also, it is a measuring on moving ground condition that the experimental values of the critical gap distances, Strouhal numbers and aerodynamic force FFT analyses. Through the experiments, we found that the momentum supply due to moving ground caused the vortex shedding at the lower critical gap distance rather than that of fixed ground. The horizontal and vertical fences increase the critical gap distance and it can suppress the vortex shedding. Consequently, the stability characteristics of the bluff body near a moving ground could be effectively enhanced by the simple passive control such as the vertical fences.

• Journal of Ship and Ocean Technology
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• v.8 no.4
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• pp.1-9
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• 2004

High lifting devices used for control purposes have received much attention in the marine field. Hydrofoils for supporting the hull, roll stabilizer fins for developing the motion damping performance, rudders for maneuverability are the well-known devices. In the present study, the ability of the rudder with flap to produce high lift was analyzed. The boundary layer control, one of the flow control techniques, was adopted. Especially, to build the blown flap, a typical and representative type of a boundary layer control, a flapped rudder was designed and manufactured so that it could eject the water jet from the gap between the main foil and the flap to the flap surface tangentially. And it was tested in the towing tank. Simultaneously, to know the information about the 2-dimensional flow field, a fin model with similar characteristics as the rudder model applicable for the motion control was made and tested in the cavitation tunnel. In addition, local flow measurements were carried out to obtain physical information, for example, a surface pressure measurement and flow visualization around the flap. And CFD simulation was used to obtain information difficult to collect from the experiment about the 2-dimensional flow.