• Journal of computational fluids engineering
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• v.19 no.4
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• pp.80-85
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• 2014

High-volume low-speed (HVLS) fans are one category of ceiling fan installed in large enclosings such as warehouses, large barns and health clubs in order to generate comfortable air circulation. As a rotary blade, aerodynamic performance of a HVLS fan is predominantly related to its airfoil(s), and the pitch and twist angles. This paper first, investigates the effects of airfoil on the performances of three different HVLS fans with NACA 5414, 6413 and 7415 airfoils. The fans have six untwisted blades with the diameter of 6 m and rotate at 60 RPM. The blades pitch angels are $12^{\circ}$, $12^{\circ}$ and $13^{\circ}$, respectively. The results are presented in the form of the aerodynamic forces and moments, volumetric flow rate and streamlines. Regarding the volumetric flow of air, the results show that the model with NACA 7415 has the best performance. Hence, two other HVLS fans with the same airfoil but, with four and five blades are studied in order to investigate the effects of number of blades. From the point of view of air circulation still the six-bladed fan is the best one; however, the five-bladed fan is more efficient in power consumption.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.156-162
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• 2011

The preliminary design stage of helicopters consists of various operations and in each operation design several detailed analysis tasks are needed. The analysis tasks include performance and the required power estimation. In helicopter design, those are usually carried out by adopting the momentum theory. In this paper, an explicit form of computational analysis based on the blade element theory and uniform/non-uniform inflow model is developed. The other motivation of the present development is to obtain trim and required power estimation for various helicopter configurations. Sectional and hub loads, power, trim, and flapping equations are derived by using a symbolic tool. Iterative computations are carried out till convergence is achieved in the blade response, inflow, and trim. The predictions regarding the trim and power estimation turn out to be correlated well with the experimental results. The effect of inflow is further investigated. It is found that the present prediction for the lateral cyclic pitch angle is improved with the non-uniform inflow model as compared to that by the uniform inflow model. The presently improved trim and power estimation will be useful for future helicopter sizing and performance analysis.

• Journal of the Korean Institute of Gas
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• v.24 no.3
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• pp.47-53
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• 2020

In this study, the optimization design data was presented by analyzing the performance and durability of the cooling fan by one-way fluid-structure interaction analysis of the cooling fan shape used in the engine generator. For this purpose, a steady-state analysis was performed on the flow field inside the cooling fan, and the durability was analyzed by using the steady-state calculation results as input data for structural analysis. Six types were modeled for fluid analysis by changing the blade and sweep angle of the cooling fan, and the ratio of mass flow rate and torque was best in A type, but B type with relatively large mass flow rate was the best. It was judged to have flow performance. As a result of examining the structural analysis by setting the four blade thickness of the B type selected through the fluid analysis, it was judged that B Type-3 is the most suitable when considering the fatigue safety factor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.731-738
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• 2012

In this study, the evaluation of the aerodynamic characteristics of the NREL Phase VI Rotor System has been performed, for the 7 m/s upwind case using commercial FEA and CFD tools which are ANSYS Mechanical 12.1 and CFX 12.1. The initial operating conditions of the rotor blade include a $3^{\circ}$ tip pitch angle. A numerical simulation was carried out on only the rotor parts, excluding the tower structure based on the equivalent stiffness model, to consider the aeroelastic effect for the numerical simulation using the loosely coupled 2-way fluid-structure interaction method. The blade root bending moment was monitored in real time to obtain reasonable results. To verify the analysis results, the numerical simulation results were compared with the measurements in the form of the root bending moment and the pressure distributions of the NREL/NASA Ames wind tunnel test.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.10 s.103
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• pp.1177-1185
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• 2005

This paper investigates the noise radiated by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. At frequencies above the critical frequency, all wavenumber components of turbulence excite propagating cascade modes, and cascade effects are shown to be relatively weak. In this frequency range, acoustic power was shown to be approximately proportional to the number of blades. Based on this finding at high frequencies, an approximate expression is derived for the power spectrum that is valid above the critical frequency and which is in excellent agreement with the exact expression for the broadband power spectrum. The approximate expression shows explicitly that the acoustic Power above the critical frequency is proportional to the blade number, independent of the solidity, and varies with frequency as ${\phi}_{ww}(\omega/W$), where ${\phi}_{ww}$ is the wavenumber spectrum of the turbulence velocity and W is mean-flow speed. The formulation is used to perform a parametric study on the effects on the power spectrum of the blade number stagger angle, gap-chord ratio and Mach number. The theory is also shown to provide a close fit to the measured spectrum of rotor-stator interaction when the mean square turbulence velocity and length-scale are chosen appropriately.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.6
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• pp.761-768
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• 1999

This paper is studied to find the optimum condition of double-inlet Sirocco fan installed in an indoor PAC for low noise operation by the Taguchi method. The goal of this study is to obtain the best combination of each control factor which results in a desired flowrate of Sirocco fan with minimum variability. In this study, the parameter design of the Taguchi method is adopted for robust design by the dynamic characteristic analysis using orthogonal arrays and S/N ratios. The flowrate measurements are conducted by using a multiple-nozzle-type fan tester according to the orthogonal array L9($3^4$). The results of this study can be summarized as follows ; (i) The optimum condition of control factor is a set of where A is an inner to outer diameter ratio($D_1/D_2$), B is a width to outer diameter ratio($L/D_2$), C is a blade attachment angle(${\theta}$) and D is a number of blade(Z), (ii) The flowrate under the optimum condition satisfies the equation $y=0.0384{\cdot}M$ where M is a signal factor, namely number of revolution. The flowrate performance improves about 7.3% more largely as compared with the current condition, which results in about 35RPM reduction of number of revolution for the target flowrate $18.5m^3/min$, and (iii) The sensitivity analysis shows that the major factors in contribution to flowrate performance are A, B, and D ; the percentage contributions of each control factor are 44.01%(Z), 26.77%($D_1/D_2$) and 20.42%($L/D_2$).

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.1
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• pp.9-14
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• 2009

A numerical investigation was performed based on the Reynolds-Averaged Navier-Stokes(RANS) equations for the two-dimensional unsteady flow around a vertical axis turbine(VAT) with three or four blades. VAT is one of the promising devices for tidal current energy conversion. The geometry of the turbine blade was $NACA65_3$-018 airfoil, for which CFD analysis using Fluent was carried out at several angles of attack and the results were compared with the corresponding experimental data for validation and calibration. Then CFD simulations were carried out for the whole vertical axis turbine with a two-dimensional setup. The CFD simulation demonstrated the usefulness of the method to study the typical unsteady flows around VATs and the results showed that the optimum turbine efficiency could be achieved for carefully selected combinations of the number of blade and Tip-Speed Ratio(TSR).

• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.171-176
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• 2001

Plasma Display Panel(PDP) is a type of flat panel display utilizing the light emission produced by gas discharge. Barrier Ribs of PDP separating each sub-pixel prevents optical and electrical crosstalks from adjacent sub-pixels. Mold for forming barrier ribs has been newly researched to overcome the disadvantages of conventional manufacturing process such as screen printing, sand-blasting and photosensitive glass methods. Mold for PDP barrier ribs have stripes of micro grooves transferring glass-material wall. In this paper, Stripes of grooves of which width 48${\mu}{\textrm}{m}$ and 270${\mu}{\textrm}{m}$, depth 124${\mu}{\textrm}{m}$, pitch 274${\mu}{\textrm}{m}$ was acquired by machining hard and brittle materials of WC, Silicon, Alumina with dicing saw blade. Maximum roughness of the bottom and sidewall of the grooves was respectively 120nm, 287nm in grooving WC. Maximum tilt angle caused by difference between upper-most width and lower-most width was 2$^{\circ}$. Maximum Radius of bottom curvatures was 7.75${\mu}{\textrm}{m}$. This results satisfies the specification for barrier ribs of 50 inch XGA PDP if the groove form of mold was fully transferred to the barrier ribs. Barrier ribs were formed with Silicone rubber mold, which is transferred from grooved hard materials. Silicone rubber mold has elasticity accommodating the waveness of lower glass plate of PDP.

• Journal of Biosystems Engineering
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• v.42 no.4
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• pp.283-292
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• 2017

Purpose: Japanese Apricot, a type of plum, has various medicinal and economical applications. Plums are quite popular worldwide, but their deseeding remains a serious impediment to their processing. Therefore, a plum (Japanese Apricot) seed remover (PSR) was developed that can use various types of cutters according to the purpose of the plum processing, and its performance was evaluated. Methods: The proposed PSR, which allows multipurpose cutters, namely, zero-, two-, and four-blade cutters, to be installed, was first designed and manufactured. To identify appropriate parameters related to the cutting pressure, plums were harvested from three regions during three harvesting periods, and their geometrical and mechanical properties were measured. After application of the parameters related to the cutting pressure, a performance test was carried out on both fresh and frozen plums by identifying the ratios of the flesh recovery, seed recovery, seed breakage, deseeding efficiency, and machine efficiency. Results: The results show that, using the proper calculation of the processing parameters, 100% deseeding efficiency was facilitated regardless of the type of cutter used. However, in the case of a four-blade cutter, there are significant differences in the flesh recovery ratio according to the plum setting angle. Between the fresh and frozen plums, all cutters showed a significantly better flesh recovery ratio for the case of fresh plums. Conclusions: This machine will advance the plum processing technology, and eventually help the plum industry flourish.

• Journal of Biosystems Engineering
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• v.42 no.2
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• pp.80-85
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• 2017

Purpose: In this study, we attempted to analyze, by using a high-speed camera, the cutting shape as a function of cutting speed and feed rate. We compared the differences in cutting shape between domestic and foreign combines. Methods: Experiments were performed using plastic straws, and the results of two combine cutting blades, one from the Daedong Industry and one from Kuboda, were compared. The quality and performances of cutting were measured at three cutting positions: center and 68 cm to the left and right of the center. The feed rates were 0.6 m/s, 1.1 m/s, 1.6 m/s, and the cutting speeds were 600 RPM, 990 RPM, 1,380 RPM. For each speed, the cutting shape was measured three times, and the entire procedure was also repeated three times. Results: In the experiments, the domestic cutting blade achieved better results than the Japanese cutting blade. These results were obtained by studying the combination of feed rate and cutting speed, with the domestic combine attaining approximately 80% performance of the Japanese combine. We believe that additional data analysis is required, obtained from field experiments. Conclusions: The domestic cutting knives achieved better results than the Japanese cutting knives. These results are estimated from experiments conducted with different feed rates and cutting speeds; an in-depth analysis will require experiments in the real field with actual combines and a combination of multiple variables. Repeating the investigation on the length differences, broken and cut angle with various combinations of feed rate and cutting speed, will surely help to find the optimal cutting speed.