• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.39-45
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• 2010

The optimal design is needed for the blade geometry of the quad-rotor blades which is mainly used for Unmanned Aerial Vehicle. To do this, it is important to analyze the wakes under the blades. In the present study, the flow around the rotating blades was analyzed using PIV(Particle Image Velocimetry) and CFD(Computational Fluid Dynamics). The maximum axial velocity was measured at about 60% position toward the radial direction of the blade. The positions of vorticities in the test section obtained by PIV and CFD were turned out to be almost alike. The values in the difference of pressure coefficients at the upper and the lower blades were increased depending on the radial direction. Then, the values were decreased at the blade tip. The data of the flow analysis in the present study are expected to be served as the design of blades and ducts for the thrust improvement in the future.

• Journal of Sensor Science and Technology
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• v.18 no.6
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• pp.461-466
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• 2009

This paper represents a piezoelectric ultrasonic linear actuator with flexural vibration mode. The actuator is composed of two piezo ceramics, the elastic body, and the connecting tip. It is driven by the frictional force between the connecting tip and the linear motion guide. Unimorph actuators have flexural vibration. Its middle point is fixed so that suitable to the flexural vibration of $3/2\lambda$. These vibrations contribute to elliptical motion by mixed mode between longitudinal and transverse mode. It was generated when the ultrasonic electrical signals with 90 degree phase difference are applied to two ceramics. A linear movement can be easily obtained using the elliptical motion. The ATILA, FEM simulator has been used to design actuator and verify the kinetic and dynamic analysis. We used the ceramics of $20\times10\times1$ mm size and confirmed the flexural vibration of the $3/2\lambda$ at the 79 kHz through the scanning of 3D-vibrometer. The maximum velocity of actuator was 221 mm/sec and the thrust force of actuator was 2.7 N in 200Vp-p of additional voltage.

• Aerospace Engineering and Technology
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• v.3 no.1
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• pp.197-204
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• 2004

A design of regenerative cooling system of 30 ton level thrust combustion chamber for ground test has been performed. The 1-D design code has been validated by comparing with the heat flux of the NAL calorimeter for high chamber pressure and water-cooling performance of the ECC engine of MOBIS. The present design code has been confirmed to predict accurately the heat flux and water-cooling performance for high chamber pressure condition. The maximum hot-gas-side wall temperature is predicted to be about 720 K without thermal barrier coating and the coolant-side wall temperature is less than the coking temperature of RP-1. The coolant temperature rises nearly 100 K with thermal barrier coating when Jet-A1 is used as coolant.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.135-140
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• 2007

An analysis has been conducted of the optimal condition to maximize the specific impulse for a liquid rocket engine with film cooling. The present engine performance has been compared with the published conceptual design to be verified satisfactorily accurate. The optimal combination of film coolant flow rate and the regenerative cooling capacity has been found for maximum specific impulse. The optimal fuel pump pressure increases and the optimal film coolant flow decreases for a larger thrust engine. Higher turbine inlet temperature increases both the fuel pump pressure and the film coolant flow rate as the optimal condition. The coking temperature has the same qualitative effect as the turbine inlet temperature.

• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.4
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• pp.124-129
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• 2008

Design practice has been made on an oil-less scroll air compressor as an air supply device for a 2 kW fuel cell system where air pressure of 2 bar and flow rate of 120 liter/min are required. Basic structure of the scroll compressor includes double-sided scroll wrap for the orbiting scroll driven by two crankshafts connected to each other by a timing belt. These features can eliminate thrust surface which otherwise would produce frictional heat and jeopardize reliable operation of the orbiting scroll and the scroll element's deformation as well. This study focuses on optimum scroll wrap design; orbiting radius has been chosen as an independent design parameter. As the orbiting radius changes, scroll sizes such as scroll base plate and discharge port diameters change accordingly. Gas compression-related losses and mechanical loss also change with the orbiting radius. With a scroll base plate diameter of 120mm at most and discharge port of at least 10mm, the orbiting radius should be within the range of 2.5-4.0mm. With this range of the orbiting radius, it was estimated by performance analysis that the compressor efficiency reached to a maximum of ${\eta}_c$=96% at the orbiting radius of $r_s$=3.5mm for the scroll wrap height-to-thickness ratio of h/t=5.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.76-83
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• 2004

A Propulsion System of the CRW(Canard Rotor Wing) type UAV(Unmanned Aerial Vehicle) was composed of the turbojet engine to generate the propulsive exhaust gas, and the duct system including main and rotary ducts, the nozzle subsystem including main and tip jet nozzle for three flight modes such as lift/landing mode, low speed transition flight mode and high speed forward flight mode. Transient simulation performance utilized the ICV (Inter-component volume) method and simulated using the SIMULINK. Transient performance analysis was performed on 3 cases. Fuel flow schedules to accelerate from Idle to maximum rotational speed were divided into the step increase of the most severe case and ramp increase cases to avoid the overshoot of turbine inlet temperature, and variations of thrust and the turbine inlet temperature were investigated in some transient analysis cases.

• Journal of Mechanical Science and Technology
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• v.20 no.10
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• pp.1753-1764
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• 2006

A U-80 propeller and its modified version, U-75 propeller, are used for a micro air vehicle. The performance characteristics of a U-80 propeller and a U-75 propeller have not much known in the published literature. Thus, their aerodynamic characteristics are investigated using a lifting surface numerical method. The lifting surface method is validated by comparing computed results with measured data in a wind tunnel. From the computed results, it is found that the U-75 propeller produces larger thrust with higher efficiency than the U-80 propeller. To enhance the performance of these propellers, a new propeller is designed by following the sequential design procedures with the design parameters such as hub-tip ratio, maximum camber and its position, and chord length distribution along the radial direction. The performance of the designed propeller is shown to be improved much comparing with those of both the U-80 and U-75 propellers.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.4
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• pp.160-169
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• 1999

Linear pulse rootor (LPM) be suitable a field where smooth linear rootion of high precision is required, because it's structured with minute teeth pitch in airgap of between and stator and roover(forcer). Force and position of LPM are effected sensitively by the teeth pitch, air gap, permanent magnet and excitation current. So, LPM is much important to analyze the force characteristics. llis paper was awlied to perrreance roothed for force calculation at airgap. The airgap of LPM is maintained from the pressure generated by an air-bearing. Simplified airflow and permeance methods will be used to calculate the air gap under static conditions. Therefore, the maximum available force is then derived using the coenergy method with variable air gap, also normal force and linear thrust was acquired from variable minute displacement 1[mm]. 1[mm].

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.5
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• pp.824-829
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• 2015

The rotary type testing machine undergoes mechanical stress as an external force is applied. In case of the rotary type testing machine, even a tiny flaw results in a fatal demage because the size of the machine is huge. Therefore, when designing the rotary type testing machine, it is necessary to secure a safety factor with the mechanical stress analysis in order to prevent the machine from being destroyed due to scattering or transformation of rotating field. This thesis proposes a LSM rotary type tesitng machine which rotates at the speed of up to 600km/h. And the mechanical stress is considered in order that the safety factor remains above 1.5 at the maximum speed. In addition, because normal force as well as thrust occurs in the machine, the normal force exerted was considered through the strength analysis. Finally, a design plan which enables to weaken the normal force affecting the rotary type testing machine is introduced and its validity is proved by the results of FEM analysis.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.70-77
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• 2000

Supersonic Dual Bell Nozzle (SDBN) is an altitude-adaptive propulsion nozzle achieved only by a nozzle wall inflection. In order to investigate the altitude adaptive capability and the effectiveness of this nozzle concept, the present study addresses a computational work of the flow through SDBN. Several types of the SDBNs are tested for a wide range of the pressure ratio which covers from an over-expended flow to a fully under-expended flow at the exit of the SDBN. Axisymmetric, compressible, Wavier-Stokes equations are numerically solved using a fully implicit finite volume differencing scheme. The present computational results reveal that the base nozzle length affects the shock wave system occurring inside SDBN. For a quit wide range of the pressure ratio the flow separation occurs at the nozzle inflection point. It is found that the maximum thrust coefficient is obtainable for the correct expansion state at the exit of SDBN.