• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.1533-1539
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• 2013

In the present study, we compared the theory with CFD data about the boundary layer thickness, displacement thickness and momentum thickness. According to the freestream velocity, larminar and turbulent is decided and affect to the flow patterns around the airfoil The boundary layer thickness, displacement thickness and momentum thickness affect to the aerodynamic characteristics of the airfoil(e.g. lift, drag and pitching moment). The separation point is affected by varying angle of attack. In the present study, we used the Joukowski airfoil(c=1), and NACA0012 airfoil was used at CFD. The chord Reynolds number is $Re_c$=3,000, 700,000, respectively and the freestream velocity is 0.045, 10 m/s, respectively. In this paper, the data was a good agreement with that of experimental results, so we can analyze the various airfoil models.

• Journal of Aerospace System Engineering
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• v.13 no.5
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• pp.32-38
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• 2019

The flying wing configuration with high sweep angles and rounded leading edge represent a complex flow of structures by the leading edge vortex. For control of the tailless flying wing configuration with unstable directional stability, flaperon is used. In this study, we conducted numerical simulations for a non-slender flying wing configuration with a rounded leading edge and analyzed the effect of the sideslip angle and flaperon. Through aerodynamic coefficient analysis, it was found that the effect of AoS on lift and drag coefficient was minimal and the side force and moment coefficient were markedly influenced by AoS. As the sideslip angle increased, the pitch break, which is related to the pitching moment coefficient, was delayed. Through stability analysis, the directional and lateral static stability of the flying wing configuration were increased by flaperon. Also, the structure and behavior of the leading edge vortex were analyzed by observing the contour of the pressure coefficient and the skin friction line.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.4
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• pp.273-279
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• 2011

Turbulent flow analysis around a wind turbine blade was performed to evaluate the power performance of offshore wind turbine. Fluent package was utilized to solve the Reynolds-averaged Navier-Stokes equations in non-inertial rotating coordinates. The realizable k-$\varepsilon$ model was used for turbulence closure and the grid system combining structured and unstructured grids was generated. In the first, lift and drag forces of 2-D foil section were calculated and compared with existing experimental data for the validation. Then torque and thrust of the wind turbine blade having NACA 4-series sections were calculated with fixed pitch angle and rpm. Tip speed ratio was varied by changing wind speed. In the next, three kinds of end plate were attached at the tip of blade in order to increase the power of the wind turbine. Among them the end plate attached at the suction side of the blade was found to be most effective. Furthermore, performance analysis with tilt angle and rake was also performed.

• Wind and Structures
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• v.35 no.2
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• pp.83-92
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• 2022

When the rolling stocks run on the curve, the external rail has to be lifted to a certain level to balance the centrifugal force acting on the train body. Under such a situation, passengers may feel uncomfortable, and the slanted vehicle has the potential overturning risks at high speed. This paper conducted a wind tunnel test in an annular wind tunnel with φ=3.2 m based on a 1/20^th scaled high-speed train (HST) model. The sensitivity of Reynolds effects ranging from Re = 0.37×10⁶ to Re = 1.45×106 was tested based on the incoming wind from U=30 m/s to U=113 m/s. The wind speed covers the range from incompressible to compressible. The impact of roll angle ranging from γ=0° to γ=4° on train aerodynamics was tested. In addition, the boundary layer development was also analyzed under different wind speeds. The results indicate that drag and lift aerodynamic coefficients gradually stabilized and converged over U=70 m/s, which could be regeared as the self-similarity region. Similarly, the thickness of the boundary layer on the floor gradually decreased with the wind speed increase, and little changed over U=80 m/s. The rolling moment of the head and tail cars increased with the roll angle from γ=0° to γ=4°. However, the potential overturning risks of the head car are higher than the tail car with the increase of the roll angle. This study is significant in providing a reference for the overturning assessment of HST.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.10-17
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• 2018

The size of commercial wind turbines has been increased. Generally, the pitch control is used to increase the efficiency of wind turbine. However, the pitch control has difficulty to control the local unsteady flow control which makes fatigue load and decreases the efficiency. In this research, Synthetic Jet Actuators(SJAs) are manufactured and applied into a wing section to delay flow separation and increase aerodynamic performances. The SJAs as a kind of zero-net mass-flux actuators injects and removes fluid through a small orifice with a given frequency. The SJA modules actuated by piezoelectric disks are manufactured and the aerodynamic performances are measured according to the shape of the orifice and the velocity of the jets through the wind tunnel test. It is confirmed that as the velocity of the jets are increased using rectangular shape orifice, drag force is decreased and lift force in increased.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.900-908
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• 2014

The Characteristics of the flowfields of a square prism having a small vertical plate at the upstream side was investigated by measuring of fluid force on the square prism and by visualization of the flow fields using PIV. The experimental parameters were the width ratios(H/B=0.2~0.6) of vertical plates to the prism width and the gap ratios (G/B=0~3) between the prism and the vertical plate. The drag reduction rate of the square prism was increased with H/B in case of the same G/B, and was increased and then decreased with G/B in case of the same H/B. The lift reduction rate of the square prism was hardly not affected by the width and gaps ratios, the average value was about 48.1%. In case of a square prism having a small vertical plate, the stagnation regions were represented in the upstream and downstream sides of the square prism.

• 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 Society of Naval Architects of Korea
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• v.37 no.2
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• pp.70-76
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• 2000

A numerical study on the viscous flow around a 2-dimensional circulation control foil is carried out for application on the field of naval architecture and ocean engineering. The governing equations are the RANS and the continuity equations. The equations are discretized by finite difference method and MAC method and the pressure poisson equation is calculate by a SOR method and an O-type non-staggered boundary fitted coordinate system which is overlapped near the slot is used to improve the numerical accuracy. Turbulence is approximated by a modified Baldwin-Lomax turbulence model. In the present paper, the Coanda effect on a 2-dimensional foil of a 20% thickness ellipse with modified rounded trailing edge has been numerically studied. The change in drag and lift of the foil with various jet momentums are calculated and compared to the experimental results to show good agreements.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.7
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• pp.549-557
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• 2008

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase IV wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase IV wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(${\kappa}-\;{\varepsilon}$) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.647-654
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• 2010

In this study, an efficient ornithopter aerodynamic model, which is applicable to ornithopter wing design considering fluid-structure interaction or ornithopter flight dynamics and control simulation, was proposed and experimentally validated through the wind tunnel experiments. Due to the ornithopter aerodynamics governed by unsteady low Reynolds number flow, an experimental device was specially designed and developed. A part of the experimental device, 2-axis loadcell, was situated in the non-inertial frame; the dynamic calibration method was established to compensate the inertial load for pure aerodynamic load measurements. The characteristics of proposed aerodynamic model were compared with the experimental data in terms of mean and root-mean-square values of lift and drag coefficients with respect to the flow speed, flapping frequency, and fixed angle of attack.