• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.5
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• pp.722-730
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• 2001

The local heat transfer of an axisymmetric submerged air jet impinging on a heated flat plate is investigated experimentally with the variation of mesh-screen solidity. The screen installed in front of the nozzle exit modifies the flow structure and local heat transfer characteristics. The mean velocity and turbulence intensity profiles of streamwise velocity component are measured using a hot-wire anemometry. The temperature distribution on the heated flat surface is measured with thermocouples. The smoke-wire flow visualization technique was employed to understand the near-field flow structure qualitatively for different mesh screens. Large-scale toroidal vortices and high turbulence intensity enhance the heat transfer rate in the stagnation region. For a higher solidity, turbulence intensity become higher which increases the local heat transfer at small nozzle-to-plate spacings such as L/D<6. The local and average Nusselt numbers of impinging jet from the $\sigma$(sub)s=0.83 screen at L/D=2 are about 5.6∼7.5% and 7.1% larger than those for the case of no screen, respectively. For the nozzle-to-plate spacings larger than 6, however, the turbulence intensities for all tested screens approach to an asymptotic curve and the mean velocity along the jet centerline decreases monotonically. As the nozzle-to-plat spacing increases for high solidity screens, the heat transfer rate decreases due to the reduction in turbulence intensity and jet momentum.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.8
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• pp.693-702
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• 2015

This paper presents the performance characteristics of a Darrieus-type vertical-axis wind turbine (VAWT) with National Advisory Committee for Aeronautics (NACA) airfoil blades. To estimate the optimum shape of the Darrieus-type wind turbine in accordance with various design parameters, we examine the aerodynamic characteristics and separated flow occurring in the vicinity of the blade, the interaction between the flow and blade, and the torque and power characteristics that are derived from it. We consider several parameters (chord length, rotor diameter, pitch angle, and helical angle) to determine the optimum shape design and characteristics of the interaction with the ambient flow. From our results, rotors with high solidity have a high power coefficient in the low tip-speed ratio (TSR) range. On the contrary, in the low TSR range, rotors with low solidity have a high power coefficient. When the pitch angle at which the airfoil is directed inward equals $-2^{\circ}$ and the helical angle equals $0^{\circ}$, the Darrieus-type VAWT generates maximum power.

• Solar Energy
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• v.6 no.2
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• pp.86-92
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• 1986

This paper presents the aerodynamic performances of horizontal axis wind turbines with non-twisted but taperd blades. Five configurations of blades, namely, one straight blade and four tapered blades with taper ratio of ranging from 0.1 to 0.7 have been simulated. The aerodynamic performances of the wind turbines have been determined over blade incidence angle of ranging from $2^{\circ}$ to $6^{\circ}$ and keeping same solidity and radius of them. The results are presented comparing straight blade from four tapered blades for maximum power coefficient and tip looses against variation of taper ratio. It also shows that the wind turbine with taper ratio of 0.5 has the highest maximum power coefficient than others. And wind turbines with taper ratio below 0.2 have lower values of maximum power coefficients than straight one. The tip loss of straight blade is the largest and reduces Slightly with the decrementation of taper ratio.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.379-385
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• 2010

We developed a high-efficiency, wide-operating-range centrifugal blower stage to meet the demand for reduced total energy-consumption in sewage treatment plants. We improved the efficiency of the two-dimensional impeller using a shape optimization tool and one-dimensional performance prediction tool. A limit of the throat deceleration ratio was set to maintain the stall-margin of the impeller. The low solidity vaned diffuser and return channel were designed using a sensitivity analysis with orthogonal arrays and three-dimensional steady flow simulations. The low solidity diffuser was designed in order to improve the performance in the low-flow-rate region. The return channel was designed so that the total pressure loss in the return channel was minimized. Model tests of both the conventional and optimized blower stages were carried out, and the efficiency and operating range of both stages were compared. The optimized blower stage improved in stage efficiency by 3% and in operating range by 5% compared with the conventional blower stage.

• Journal of Institute of Convergence Technology
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• v.5 no.1
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• pp.37-40
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• 2015

Numerical analyses on the aerodynamic characteristics of a counter rotating axial flow fan is carried out using the frequency domain panel method. Front rotor and rear rotor blades of a counter rotating axial fan are designed by using the simplified meridional flow analysis method with the radial equilibrium equation and the free vortex design condition, according to design requirements. Performance characteristics of a counter rotating axial flow fan are estimated for the variation of design parameters such as the hub to tip ratio, the taper ratio and the solidity. Pressure losses were higher at leading edge and hub region of rotor blades. Characteristic curve of the counter rotating fan was overpredicted without consideration of viscous effect.

• Wind and Structures
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• v.35 no.2
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• pp.93-108
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• 2022

Steel tubular towers are commonly used in UHV and long crossing transmission lines. By considering effects of the model scale, the solidity ratio and the ratio of the mean width to the mean height, wind tunnel tests under different wind speeds on twenty tubular steel tower body models and twenty-six tubular steel cross-arm models were completed. Drag coefficients and shielding factors of the experimental tower body models and cross-arm models in wind directional axis for typical skewed angles were obtained. The influence of the lift forces on the skewed wind load factors of tubular steel tower bodies was evaluated. The skewed wind load factors, the wind load distribution factors in transversal and longitudinal direction were calculated for the tubular tower body models and cross-arm models, respectively. Fitting expressions for the skewed wind load factors of tubular steel bodies and cross-arms were determined through nonlinear fitting analysis. Parameters for skewed wind loads determined by wind tunnel tests were compared with the regulations in applicable standards. Suggestions on the drag coefficients, the skewed wind load factors and the wind load distribution factors were proposed for tubular steel transmission towers.

• Korean Journal of Human Ecology
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• v.17 no.1
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• pp.151-158
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• 2008

This study examines the cooking quality, rheology, and sensory characteristics of ramyon noodles made from Korean wheat and arrowroot starch. The control was made from Australian standard wheat(ASW) and the sample was made from Korean wheat. The ratios of arrowwood starch in the sample group were 0%, 5%, 10%, 15%, 20%, 25%, and 30% respectively, and the result was as follows: the yield of the arrowwood starch was 18.8% and moisture level was 14.2%. The lightness(L), redness(a), and yellowness(b) of ASW were 92.07, 1.44, 10.22 respectively, whereas those of Korean wheat were 92.05, 1.55, 11.01, which means the two kinds of wheat showed very little difference in lightness, but Korean wheat had higher degrees of a and b than ASW. The color value of arrowroot starch is L 72.65, a 3.44, b 12.92, so it has a lower degree of lightness and higher degrees of a and b than two kinds of wheat. Dried ramyon displayed a lower degree of lightness and higher degrees of a and b than cooked ramyon, but the first decreased and a increased as we increased the ratio of arrowroot starch in it. The weight of dried ramyon did not show a significant difference among the groups. On the other hand, the weight, volume, water absorption, and the turbidity of cooked ramyon increased as we increased the amount of arrowroot starch in it. The maximum weight, solidity, and elasticity of the control group were greater than those of ramyon made from Korean wheat, but its brittleness was lower. The two groups showed the same degrees of hardness, adhesiveness, and cohesiveness. The maximum weight, solidity, and adhesiveness of the control group increased as we increased the amount of arrowroot starch in it, and the hardness and brittleness were great when the ratio of arrowroot starch was 20%; elasticity was greatest when the ratio of arrowroot starch was 15, 20, and 25%; its adhesiveness and cohesiveness did not depend on the amount of arrowroot starch in it. In the sensory characteristics evaluation, the items that showed significant differences include: appearance (p<0.01), color(p<0.01), smell(p<0.001), transparency(p<0.05), and overall acceptability(p<0.05). The ramyon earned the highest score in appearance when the ratios of arrowroot starch were 5%, 15%, and 20%. As for color and smell, it earned the highest score when it contained 20 and 25% of arrowroot starch. The transparency decreased as we increased the amount of arrowroot starch, and overall acceptability was highest when the ratio of arrowroot starch was 15%. There was a significant difference in overall acceptability between the control and the sample group. As for the loosing speed and chewiness, there was no significant difference between the two groups. When we look at the result of various tests to evaluate the cooking quality, rheology, and sensory characteristics of ramyon noodles, ramyons that contained 15 to 25% of arrowroot starch earned the high scores, and of these the one with 20% of arrowroot starch earned the highest score on all accounts.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.3
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• pp.250-265
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• 1999

Quality and distribution of the TEA(Total Enclosed Area), TSA(Twine Surface Area), solidity ratio and resistance according to the partial nets of the midwater trawl net were examined through experiment at the sea to standardize a design of the midwater trawl net.The results can be summarized as follows;1. The TEA, TSA and resistance of the trawl net were increased definitely according to increasing the scale of the trawl net, and this is the most important factor to design the trawl net.2. As the result of analysis of the distributions of the bag net was smaller than the others. Because TEA for rear end of the wing net is decreased suddenly, we can judge that the trawl net was towed irregularly. 3. The resistance distribution of the partial net was increased suddenly from central part of the bag net and was showed large value in the codend.4. The resistance of the net from the position one of three to gab net and codened charged 75% at all resistance of net.

• Transactions of the Korean Society of Mechanical Engineers
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• v.3 no.2
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• pp.60-67
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• 1979

Aerodynamic forces acting on a curved blade are computed theoretically taking into account the variation of wind speed over the blade to investigate the performance of a vertical axis wind rotor. It is shown that the rotor does not self start at the rated wind speed without a supplementary starting device and that most of the power output is contributed by the central portion of the rotor, and the use of spoilers for limiting the maximum rotational speed is needed for safety. It is also shown that provision of skew angle to the blade does not improve the starting characterstics and only reduces the maximum power output. The effects of geometric variables such as skew angle, blade solidity and ratio of the rotor height to diameter are also discussed.

• The KSFM Journal of Fluid Machinery
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• v.15 no.1
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• pp.64-69
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• 2012

Currently axial flow compressor is used primarily in a large power generation gas turbine. In this paper,the main factors to be considered when designing a axial flow compressor were compared to those of a small power generation gas turbine(DGT-5). The main design parameters was examined in the aspect ratio, solidity, as well as reaction, diffusion factor, incidence angle, etc. The results in case of a small compressor are showed a regular pattern but there were not found any specific design patterns for a large class compressor.