• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1074-1083
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• 2006

In the present study, the effect of blade rotation on blade heat transfer is investigated by comparing with the heat transfer results for the stationary blade. The experiments are conducted in a low speed annular cascade with a single stage turbine and the turbine stage is composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has a flat tip and the mean tip clearance is 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. For the experiments, the inlet Reynolds number is $Re_c=1.5{\times}10^5$, which results in the blade rotation speed of 255.8 rpm. Blade rotation induces a relative motion between the blade and the shroud as well as a periodic variation of incoming flow. Therefore, different heat/mass transfer patterns are observed on the rotating blade, especially near the tip and on the tip. The relative motion reduces the tip leakage flow through the tip gap, which results in the reduction of the tip heat transfer. However, the effect of the tip leakage flow on the blade surface is increased because the tip leakage vortex is formed closer to the surface than the stationary case. The overall heat/mass transfer on the shroud is not affected much by the blade rotation.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.272-285
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• 2004

The losses at off-design points from a compressor cascade occur due to the deviation from a design incidence angle at the inlet of the cascade. The self-noise from the blade cascade at off-design points comes from a separated boundary layer and vortex sheddings. If the incidence angle to the cascade increases, stalling in blades may occur and the noise level increases significantly. This study applied Large-Eddy Simulations (LES) using deductive and deductive dynamic SGS models to low Mach-number, turbulent flow with each incidence angle to the cascade ranging from -40$^{\circ}$ to +20$^{\circ}$ and compared numerical predictions with measured data. It was observed that the oscillating separation bubbles attached to the suction surface do not modify wake flows dynamically for cases of negative incidence angles. However, an incidence angle greater than 8$^{\circ}$ caused a separated vortex near the leading edge to be shed downstream and created stalling. The computed performance parameters such as drag coefficient and total pressure loss coefficient showed good agreement with experimental results. Noise from the cascade of the compressor is summarized as sound generated by a structure interacting with unsteady, turbulent flows. The hybrid method using acoustic analogy was observed to closely predict the measured overall sound powers and directivity patterns at design and off-design points of blade cascade.

• Ocean Systems Engineering
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• v.9 no.2
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• pp.111-133
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• 2019

Flow through a scaled horizontal axis marine current turbine was numerically simulated after validation and the turbine design was optimized. The computational fluid dynamics (CFD) code Ansys-CFX 16.1 for numerical modeling, an in-house blade element momentum (BEM) code for analytical modeling and an in-house surrogate-based optimization (SBO) code were used to find an optimal turbine design. The blade-pitch angle (${\theta}$) and the number of rotor blades (NR) were taken as design variables. A single objective optimization approach was utilized in the present work. The defined objective function was the turbine's power coefficient ($C_P$). A $3{\times}3$ full-factorial sampling technique was used to define the sample space. This sampling technique gave different turbine designs, which were further evaluated for the objective function by solving the Reynolds-Averaged Navier-Stokes equations (RANS). Finally, the SBO technique with search algorithm produced an optimal design. It is found that the optimal design has improved the objective function by 26.5%. This article presents the solution approach, analysis of the turbine flow field and the predictability of various surrogate based techniques.

• Journal of Power System Engineering
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• v.19 no.6
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• pp.19-25
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• 2015

The unsteady-state, incompressible and three-dimensional large eddy simulation(LES) was carried out to analyze the aerodynamic performance of three-dimensional small-size axial fan(SSAF) with the different depth of bellmouth. The static pressure coefficients analyzed by LES predict a little bit larger than measurements except stall region regardless of the installation depth between SSAF and bellmouth. Moreover, static pressure efficiencies analyzed by LES show about maximum 30% at the actual operating point ranges, but measurements do not. Therefore, if the blades of conventional SSAF have some more rigidity and complete dynamic balance, the aerodynamic performance of SSAF will be some more improved. In consequence, LES shows the best prediction performance in comparison with any other Reynolds averaged Navier-Stokes(RANS) method.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.235-238
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• 2000

Current diesel engines are usually equipped with turbochargers for improving fuel economy as well as meeting more stringent emission regulations. These turbochargers usually cause noise problems because they spins vey high such as 100,000 to 200,000 rpm, These noises are largely divided into whistle and whine noises. The frequency of whistle noise corresponds to their rotation speed, and the frequency of whine noise does to the multiplication of their rotation speed and the number of compressor blades. Turbocharger manufacturers developed a special type of compressor, effectively compressing air sucked from a duct; Recirculation Compressor Cover (RCC) or Map Width Enhancement (MWE). This special structure improves turbocharger's capability by expanding compressor's working area, but it seriously causes a noise problem, whine noise. There were many trials to surpress the noise occurred inside a compressor such as modification of a compressor, noise baffles or secondary measurements. However, it was currently concluded that the whine noise caused by the special compressor can not be reduced to that done by a standard compressor, and the strength difference of whine noises between the two compressors is not negligible. Thus, the standard compressor is decided to be applied to a newly developing heavy-duty diesel engine in order to resolve the turbocharger noise problem with a stiffened suction duct directly connected to a compressor.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.1
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• pp.147-154
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• 2019

In this research, a molecular dynamics system was designed and developed to calculate trajectories of molecules in nozzles and turbin blades. The Lennard-Jones potential model was used to approximate the interaction between a pair of molecules and the Verlet integration is used as a numerical method to integrate Newton's equations of motion. To compute Lennard-Jones potential functions, for the number of molecules N, the computation complexity $O(N^2)$ for interactions of all pairs of molecules is reduced to O(N) by using cutoff radius $r_c$. This was implemented to save CPU times.

• Journal of Power System Engineering
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• v.21 no.1
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• pp.70-79
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• 2017

The output power of turbine is greatly affected by the losses generated within the passage. In order to develop a better turbine or loss models, an experimental study was conducted using a linear cascade experimental apparatus. The total pressure loss and flow structures were measured at two cross-sectional planes located downstream of blade row. Measurement was conducted in a steady state for the several different locations of the blade row along the rotational direction. The blade row moved by 20 % of the pitch, and tip clearance was varied from 2% to 8%. Axial-type blades were used and its blade chord was 200mm. A square nozzle was applied and its size was $200mm{\times}200mm$. The experiment was conducted at a Reynolds number of $3{\times}10^5$ based on the chord. Nozzle flow angle sets to $65^{\circ}$ based on the axial direction and the solidity of blade row was 1.38. From the experimental results, the total pressure loss was greatly varied in the receding region than in the entering region. The flow properties within the blade passage were strongly changed according to the location of blade row.

• Archives of Plastic Surgery
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• v.48 no.5
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• pp.549-552
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• 2021

Clinical applications of stromal cells obtained mechanically from adipose tissue are quite popular methods. However, generally accepted protocols still do not exist. In this study, three new delivery methods using different protocols are presented as innovative methods in accordance with an approach called "Indication-based protocols." In mechanical methods, before cutting the fat tissue with ultra-sharp blades, which we define as "Adinizing," mixing it with different liquids such as saline or plasma provides the stromal cells in liquid form with high number and viability as a final product. At the same time, since stromal cells and extracellular matrix are preserved by mechanical methods, it was deemed appropriate to use the term total stromal cells (TOST) instead of stromal vascular fraction for this final product, unlike the product obtained with the enzyme. TOST can be combined with plasma and used for dermal filling in "solid" form. In addition to this filling effect, it will also cause a change in the tissue regeneratively. Finally, the stromal cells obtained from liquid can be applied clinically in aerosol form with the help of nebulizer. We believe that three innovative delivery methods can be used successfully in the treatment of many clinical situations in the future.

• New & Renewable Energy
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• v.7 no.3
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• pp.92-100
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• 2011

With the increased demand of clean energy and global warming measures, the renewable energy development has been increased recently. The TCP (Tidal Current Power) is one of the ocean renewable energy sources. Having the high tidal energy source in Korea, there are many potential TCP sites with strong current speed. The rotor, which initially converts the energy, is a very important component because it affects the efficiency of the entire system. The rotor performance is determined by various design parameters including number of blades, shape, sectional size, diameters and etc. However, the interactions between devices also contribute significantly to the energy production. The rotor performance considering the interaction needs to be investigated to predict the exact power in the farm. This paper introduces the optimum design of TCP turbine and the performance of devices considering the interference between rotors.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.4
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• pp.459-466
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• 2014

This paper deals with the method to classify the aircraft target by analyzing its JEM signal. We propose the method to classify the engine model by analyzing JEM spectrum using the harmonic frequency mask generated from the blade information of jet engine. The proposed method does not need the complicated logic algorithm to find the chopping frequency in each rotor stage and the pre-simulated engine spectrum DB used in the previous methods. In addition, we propose the method to estimate the precise spool rate and it reduces the error in estimating the number of blades or in calculating the harmonic frequency of frequency mask.