• Journal of Biosystems Engineering
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• v.33 no.5
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• pp.289-295
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• 2008

The task of chemical spraying has been seriously considered as an irritating and annoying job for Korean rice farmers. An agricultural unmanned helicopter was suggested to solve this problem so as the farmers to have more decent farming condition. The objectives of this study were to analyze the adoptability of an experimental rotor blade (SW05) using the CFD simulation and also to compare the simulation results with experimental results. The simulation results showed that the induced power of this rotor reached to $57{\sim}63%$ of total power and the profile power was about $37{\sim}43%$ of total power. Therefore it can be concluded that this rotor's performance characteristics were not so efficient for the size of unmanned helicopter due to the low induced power and high profile power relatively compared with ones of conventional rotors. The comparison with experimental results showed that the tested lifts were less than 70% of simulated ones at the grip pitch of $12^{\circ}$ and decreased to 40% at the $18^{\circ}$ grip pitch. Therefore, it can be concluded that the rotor was too oversized to be used for a 15.4 kW (21 PS) engine.

• New & Renewable Energy
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• v.3 no.3
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• pp.36-44
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• 2007

Most airfoils for wind turbines commercially available have been developed for aircrafts, which are operated at high Reynolds numbers. However, Reynolds numbers of wind turbines are very low compared to those of aircrafts. In other to improve wind turbine performances, airfoils for the use of wind turbine shall be designed such as S-series airfoils developed by NREL in America. The authors have designed new airfoils for wind turbines considering designated operation conditions of wind turbines and even local wind resources in Korea. The designed airfoils are characterized by improved roughness insensitivities compared to other airfoils such as S814 and S820. The developed KWA005-240 and KWA009-127 are for root and tip sections of a wind turbine blade, respectively. Although the results show much improved performances against NACA airfoils, performance data of post-stall regulation loses some accuracies due to the characteristics of the simulation tool of XFOIL. Therefore, wind tunnel experiments are required for more accurate evaluation of the designed airfoils. Currently, the experiments has been completed and the data analysis works are going on now. The final results obtained from the experiments will be published soon.

• Wind and Structures
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• v.29 no.6
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• pp.405-416
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• 2019

Aerodynamic characteristic of a small scale wind turbine under the influence of an incoming uniform wind field is studied using k-ω Shear Stress Transport turbulence model. Firstly, the lift and drag characteristics of the blade section consisting of S826 airfoil is studied using 2D simulations at a Reynolds number of 1×10⁵. After that, the full turbine including the rotational effects of the blade is simulated using Multiple Reference Frames (MRF) and Sliding Mesh Interface (SMI) numerical techniques. The differences between the two techniques are quantified. It is then followed by a detailed comparison of the turbine's power/thrust output and the associated wake development at three tip speeds ratios (λ = 3, 6, 10). The phenomenon of blockage effect and spatial features of the flow are explained and linked to the turbines power output. Validation of wake profiles patterns at multiple locations downstream is also performed at each λ. The present work aims to evaluate the potential of the numerical methods in reproducing wind tunnel experimental results such that the method can be applied to full-scale turbines operating under realistic conditions in which observation data is scarce or lacking.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.6
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• pp.609-617
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• 2014

Even though the variable pitch control of a wind turbine blade is known as an effective component for power control over the rated wind speed, it has limited applicability to small wind turbines because of its relatively high cost on the price of small wind turbine. Instead, stall control is generally applied in the blade design without any additional cost. However, stall delay can frequently be caused by high turbulence around the turbine blade, and it can produce control failures through excessive rotational speed and overpowering the electrical generator. Therefore, a passive pitch control module should be considered, where the pitch moves with the aerodynamic forces of the blade and returns by the elastic restoring force. In this study, a method to calculate the pitch moment, torque, and thrust based on the lift and drag of the rotating blade wing was demonstrated, and several effective wing shapes were reviewed based on these forces. Their characteristics will be estimated with variable wind speed and be utilized as basic data for the design of the passive pitch control module.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.8
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• pp.758-766
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• 2010

The design procedure of Solar Power UAVs is complicated because the configuration and required power for flight must be considered simultaneously as the supplied power is influenced by the wing area. In order to minimize trial and error for the Solar Power UAVs design, a systematic sizing method is proposed which can be used to determine whether a Solar Power UAV is feasible for a given mission, and to derive preliminary dimensional specification of it. The sizing procedure begins with initially assumed wing area because the power, lift, and drag of the wing are directly proportional to it. The assumed wing area and mission requirements are then used to determine step by step the airfoil specifications including lift coefficient and drag coefficient, weight, required power, and wing area. This procedure is iterated for each newly assumed wing area until the error between the assumed wing area and calculated wing area becomes significantly small enough. This sizing methodology was applied to previously developed Solar Power UAVs for validation purposes, resulting in good agreement. The methodology was also applied to determine the dimensions and specifications of the Solar Power High-Altitude Long-Endurance UAV.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.515-523
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• 2020

This study aims to improve the flow and noise performances of an axial-flow fan for cooling the machine room in a refrigerator by using airfoil-cascade analysis and surface ridge shape. First, the experimental evaluations using a fan performance tester and an anechoic chamber are performed to analyze the flow and noise performances of the existing fan system. Then, the corresponding flow and noise performances are numerically assessed using the Computational Fluid Dynamics (CFD) techniques and the Ffowcs-Williams and Hawkings (FW-H) equation, and the validity of numerical results are confirmed through their comparisons with the experimental results. The analysis for the flow of a cascade of airfoils constructed from the existing fan blades is performed, and the pitch angles for the maximum lift-to-drag ratio are determined. The improved flow performance of the new fan applied with the optimum pitch angles is confirmed. Then, the fan blades with surface ridges on their pressure sides are devised, and the reduction of aerodynamic noise of the ridged fan is numerically confirmed. Finally, the prototype of the final fan model is manufactured, and improvements in the flow and noise performances of the prototype are experimentally confirmed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.492-497
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• 2011

Helicopter uses a rotor system to generate lift, thrust and forces, and its aerodynamic environment is generally complex. Unsteady aerodynamic environment arises such as blade vortex interaction. This unsteady aerodynamic environment induces vibratory aerodynamic loads and high aeroacoustic noise. Those are at N times the rotor blade revolutions (N/rev). But conventional rotor control system composed of pitch links and swash plate is not capable of adjusting such vibratory loads because its control is restricted to 1/rev. Many active control methodologies have been examined to alleviate the problem. The blade using active control device manipulates the blade pitch angle at arbitrary frequencies. In this paper, Active Trailing-edge Flap blade, which is one of the active control methods, is designed to modify the unsteady aerodynamic loads. Active Trailing-edge Flap blade uses a trailing edge flap manipulated by an actuator to change camber of the airfoil. Piezoelectric actuators are installed inside the blade to manipulate the trailing edge flap.