• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.1
• /
• pp.12-21
• /
• 2010

This paper focuses on the hover performance experiment of a small-scale single rotor in partial ground conditions. In this study, small-scale rotor blade rotating device and floor panel are used to include partial ground effect. Thrust and torque were measured with varying collective pitch angles at fixed rotor rotating speed. The overlap distance between rotor and ground is d, the rotor diameter is D. It was shown that the ground effects have little effect on the rotor performance until d/D is 0.25. Four blade rotor has more increased thrust and more reduced power than those of two blade rotor because of stronger ground effect. In addition, it was also found that the thrust increases as a collective pitch angle become smaller. Based on these experiment results, we deduced new empirical equation considered blade number and partial ground effect.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.2
• /
• pp.143-148
• /
• 2007

An impulse turbine, which is a main component of a liquid rocket engine, needs to be a small size with light weight and generate large power. Since the impulse turbine is being operated under complicated supersonic conditions, flow analysis and performance prediction largely depend on CFD technique. In order to increase the reliability of the prediction code, however, it often requires an experimental data to compare. In this research a rotating turbine rotor with multiple blades is simulated with a two-dimensional stationary cascade to check the effect of major flow parameters. Mach number is measured at nozzle exit by using a pitot tube and the blade thrust was also measured with a load cell. The measured thrust coefficient and the power are compared well with the designed conditions, which proves the design procedures are properly taken.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.12
• /
• pp.1087-1096
• /
• 2011

The purpose of current study is to develop and verify the newly developed solver for analyzing rotor flow using the open-source code. The algorithm of standard solver, OpenFOAM, is improved to analyze the rotor inflow with and without fuselage. For the calculation of the rotor thrust, the virtual blade method based on the blade element method is employed. The inflow velocities on the rotor disk used to specify the effective angle of attack, have been included in the solver. The results of the current rotor inflow analysis are verified by comparing with other experimental and numerical results. It was confirmed that the modified solver provides satisfactory results for rotor-fuselage interaction problem.

• The Journal of the Acoustical Society of Korea
• /
• v.32 no.5
• /
• pp.369-376
• /
• 2013

Using Lowson's acoustic analogy, low frequency noise of a wind turbine (WT) is predicted in time domain and the noise sources contributing to the low frequency noise is analyzed. To compute averaged pressure distribution on blades of the WT as noise source, XFOIL is utilized. The blade source domain is divided into several segments along the span direction to compute force exerted on air surrounding the blade segments, which is used as input for noise prediction. The noise sources are decomposed into three terms of force fluctuation, acceleration and velocity terms and are analyzed to investigate each spectral contribution. Finally, predicted spectra are compared with measured low frequency noise spectrum of a wind turbine in operation. It is found that the force fluctuation component contributes strongly in low frequency range with increasing wind speed.

• Journal of the Korea Fashion and Costume Design Association
• /
• v.21 no.4
• /
• pp.27-42
• /
• 2019

This paper tried a detailed approach to identify the correlation among basic elements that influenced the change of forms of the Po. To this end, the subjects were limited to the clothing from the 15th to the 18th century, which was found in the tombs of the period of Pyeonbokpo. The total number of excavated artifacts measured directly is 6 and other correctly described excavated artifacts for a total of 54 items. Per period and element, the types of collars and Seop were presented by classifying collars in 4 types, and Seop in 3 types. On the basis of the classification, the relics selected in this paper were analyzed considering the appearance, period, and rate per type of each element. The type and the change of forms of each element per period, with the focus on the appearance, were identified and the factors influencing the change of forms per element and the correlation between such factors were investigated. The representative type in the first period included dual collars, dual Seop and the representative type in the second period was characterized by a shawl collar and a dual Seop joining the pieces. The representative type in the third period was characterized by round collars and a short Seop. The elements determining the forms of Po, including collars and Seop, had a correlation to the lapse of time and had been systematically influencing each other. Furthermore, the overall change of form was caused due to the social functions as well as the supplementary function of keeping balance among the elements and accordingly, the change of forms was think characterized per period.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.5
• /
• pp.1-8
• /
• 2002

The performance of MAV(Micro Air Vehicles) propellers is highly affected by the aerodynamic characteristics of a 2-D blade airfoil shapes. XFOIL is used to predict the lift and drag coefficients in low Reynolds Number flows. ARA-D 6%, which shows a good performance in low Reynolds Number regions, is selected as a blade airfoil. The 3-D propeller blade shape is optimized with the minimum energy loss condition, and the distribution of aerodynamic coefficients of ARA-D 6% is calculated. The designed optimal blade is compared with the Black Widow's propeller blade shape in the same conditions. The results indicate that the designed propeller installed in MAV can provide a good performance.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.5
• /
• pp.513-520
• /
• 2014

An unmanned aerial vehicle (UAV) should be designed to be as small and lightweight as possible to optimize the efficiency of changing the blade shape to enhance the aerodynamic performance, such as the thrust and power. In this study, a computational fluid dynamics (CFD) simulation of an unmanned multi-rotor aerial vehicle in hover mode was performed to explore the thrust performance in terms of the blade rotational speed and blade shape parameters (i.e., taper ratio and twist angle). The commercial ADINA-CFD program was used to generate the CFD data, and the results were compared with those obtained from blade element theory (BET). The results showed that changes in the blade shape clearly affect the aerodynamic thrust of a UAV rotor blade.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.7 s.238
• /
• pp.878-885
• /
• 2005

The water jet impingement cooling is one of the techniques to remove the heat from high heat flux equipments. Local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer are investigated in the fee surface jet and submerged jet. Boiling is initiated from the farthest downstream and increase of the wall temperature is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance fur H/W$\le$1 causes significant increases and distribution changes of heat transfer. Developed boiling reduces the differences of heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to nozzle collar, Hc are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increases as decreased spacing of collar to heated surface. Heat transfer is enhanced fur region from the stagnation to x/W$\~$8 in the free surface jet and to x/W$\~$5 in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet comparing with higher velocity condition. It is because the increased velocity by collar is de-accelerated downstream.

• Animal Systematics, Evolution and Diversity
• /
• v.9 no.2
• /
• pp.261-280
• /
• 1993

The marine hydroids of Cheju Island in this work identified into 46 species and/or subspecies of 25 genera in 10 families. Of which four species: Rhizocaulus chinensis, Obelia bicuspidata, Sertularia desmoides and Plumularia spinulosa are new to the hydroid fauna of Cheju Island and four species: Hebella parastica, Campanularia groenlandica, Campanularia everta and Sertulareffa natalensis are new to the Korean fauna. Adding these eight species to the previous known species (83 species and/or subspecies) in Cheju Island, the hydroid fauna in Cheju Island identified up to date consists of 91 species and/or subspecies of 41 genera in 12 families. Macrorhynchia phoenicea is dominant species which occur in 10 points, Aglaophenia suensonii in eight points. 71 species (78%) occur in Songsanp'o, 43 species (47%) in Munsom, 26 species (29%) in Supsom, 13 species (14%) in Wimi-ri and 11 species (12%) in P - omsom in order. Thirty-three percent (30 species) of the hydroids of Cheju Island was only found in Cheju Island.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.9
• /
• pp.16-26
• /
• 2005

The aerodynamic design of a proprotor for the Smart UAV adopting tiltrotor aircraft concept is conducted in this study. Since proprotor of tiltrotor aircraft is operated at both rotary and fixed wing mode with single configuration rotor, the proprotor has to be designed to meet performance requirements for both flight modes. The aerodynamic design of proprotor is accomplished by combining three sources of data - the proprotor performance data, the aerodynamic data of vehicle, and the performance data of engine. The performance analysis code for proprotor is based on the combined momentum and blade element theory and validated by comparison with the TRAM data. In order to design configuration for a proprotor satisfying requirements for both rotary and fixed wing mode, various kind of performance maps are constructed for many performance and configuration parameters. From the analysis the twist angle of 38 degrees and the solidity of 0.118 are decided to be the optimal geometric parameters for both operating conditions.