• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.45 no.1
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• pp.34-45
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• 2009

In this study, the hydrodynamic coefficients were measured using various nettings to analyze the change of drag coefficients and lift coefficients as a basic study for deriving hydrodynamic coefficients. The data on hydrodynamic force obtained from the flume tank tests were used to compare and analyze the hydrodynamic coefficients based on Reynolds number. Standardized hydrodynamic coefficients were then assumed during the analysis procedures. The hydrodynamic coefficients were measured using the 9 kinds of nettings in which had the same total projected area with different diameters and mesh-grouping ratio. These different netting systems : mesh-grouping ratio. The results of the test of nettings were as follows; First, the drag coefficients of nettings increased when the higher attack angles applied, and decreased with the increased flow speed and netting twine diameter. Second, the lift coefficients of nettings showed the increased values until the attack angle 30 degree, but decreased for the attack angle over 40 degree. Third, the hydrodynamic coefficients of netting decreased as the Reynolds number increased, and reach at slightly states in the highest numbers. Fourth, the hydrodynamic coefficients were derived from a functional formula considering attack angles and Reynolds number, and presented in the three dimensional space.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.217-220
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• 2006

The lift and drag forces produced by a wing of a given cross-sectional profile are dependent on the wing planform and the angle of attack. Aspect ratio is the ratio of the wing span to the average chord. For conventional fixed wing aircrafts, high aspect ratio wings produce a higher lift to drag ratio than low ones for flight at subsonic speeds. Therefore, high aspect ratio wings are used on aircraft intended for long endurance. However, birds and insects flap their wings to fly in the air and they can change their wing motions. Their wing motions are made up of translation and rotation. Therefore, we tested flapping motions with parameters which affect rotational motion such as the angle of attack and the wing beat frequency. The half elliptic shaped wings were designed with the variation of aspect ratio from 4 to 11. The flapping device was operated in the water to reduce the wing beat frequency according to Reynolds similarity. In this study, the aerodynamic forces, the time-averaged force coefficients and the lift to drag ratio were measured at Reynolds number 15,000 to explore the aerodynamic characteristics with the variation of aspect ratio. The maximum lift coefficient was turned up at AR=8. The mean drag coefficients were almost same values at angle of attack from $10^{\circ}$ to $40^{\circ}$ regardless of aspect ratio, and the mean drag coefficients above angle of attack $50^{\circ}$ were decreased according to the increase of aspect ratio. For flapping motion the maximum mean lift to drag ratio appeared at AR=8.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.1
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• pp.49-56
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• 2003

The hydrodynamic interference between two circular cylinders in tandem and side by side arrangements was investigated by measuring of lift and drag on each cylinder. The time variations of interference lift and drag coefficients in each arrangement were observed at center-to-center pitch ratios of P/D=1.25 and 2.5 and Reynolds number of $Re=1.5\times10^4$. Average interference lift and drag coefficients were also observed at pitch ratios from P/D=1.25 to 2.5 and Reynolds number from $Re=1.5\times10^4$ to $1.5\times10^4$. The hydrodynamic interference between two circular cylinders differed with the shape of the arrangement and the pitch ratio, but the characteristics were revealed by measuring of lift and drag on each cylinder.

• Wind and Structures
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• v.28 no.3
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• pp.141-153
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• 2019

In this study, we have focused on commonly used 14 different small wind turbine airfoils (A18, BW3, Clark Y, E387, FX77, NACA 2414, RG 15, S822, S823, S6062, S7012, SD6060, SD7032, SD7062). The main purpose of the study is to determine the lift, drag and lift/drag coefficients of these airfoils with numerical analysis and to verify 2 best airfoil's results with experimental analysis. Airfoils were determined from past studies on small wind turbines. Numerical analyzes of the airfoils were done with Ansys Fluent fluid dynamics program. Experimental analyzes were done at wind tunnel in Erciyes University, Turkey. Lift and drag coefficients of these airfoils were determined for 50,000-100,000-200,000 Reynolds numbers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.277-286
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• 1989

Turbulent flows around two-dimensional vehicle-like bodies in ground proximity are numerically simulated. The Reynolds averaged Navier-Stokes equations with a k-.epsilon. turbulence model are numercally solved, and a body-fitted coordinate system is used. It is shown that the simulation is acceptable in comparison with limitted data measured in the wind-tunnel. According to numerical simulations, drag coefficients are under-estimated and lift coefficients are over-estimated during the model test in the wind-tunnel if the ground is fixed. Such ground effects are reduced as Reynolds number is increased. Reducing the gap between the vehicle and the ground make drag coefficients smaller and lift coefficients larger. The changes in static pressure distributions on the bottom and the rear surface play dominent roles in determination of the drag and the lift of the body in ground proximity. Drag component less than 10% of the total amount is contributed by skin-frictions. When the slant-angle of the body is reduced, the drag shows its minimum value and the lift shows its maximum value at about 22 degree.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.68-74
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• 2012

Near-wall effect on wakes behind particles is one of the important factors in precise tracking of particles in turbulent flows. However, most aerodynamic force models for particles did not fully consider the wall effect. In the present study, we focused on changes of hydrodynamic forces acting on a particle depending on wall proximity. To this end, we developed an immersed boundary method with multi-direct forcing incorporated to a fully implicit decoupling procedure for incompressible flows. We validate the present immersed boundary method through two-dimensional simulations of flow over a circular cylinder. Comprehensive parametric studies on the effect of the wall proximity on the drag and lift forces acting on an immersed circular cylinder in a channel flow are performed in order to investigate general flow patterns behind the circular cylinder for a wide range of Reynolds number (0.01 ${\leq}$ Re ${\leq}$ 200). As the cylinder is closer to the wall, the drag coefficient decreases while the lift coefficient increases with a local maximum. Maximum drag and lift coefficients for different wall proximities decrease with increment of Reynolds number. Normalized drag and lift coefficients by their maximum values show universal correlations between the coefficients and wall proximity in a low Reynolds number regime (Re ${\leq}$ 1).

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.849-863
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• 2006

IBM (Immersed Boundary Method) with feedback momentum forcing was applied to stationary and moving bodies. The capability of IBM to treat the obstacle surfaces, especially with moving effect has been tested for two dimensional problems. Stationary and oscillating cylinders were simulated by using IBM based on finite volume method with Cartesian coordinates. For oscillating cylinder, lateral and vertical motions are considered, respectively. Present results such as time histories of drag and lift coefficients for both stationary and oscillating cases are in good agreement with previous numerical and experimental results. Also, the instantaneous wake patterns of oscillating cylinder with different oscillating frequency ratios well represented those of previous researches. More feasibility study for IBM has been carried out to two oscillating cylinders. Drag and lift coefficients are presented for two cylinders oscillating sinusoidally with phase difference of $180^{\circ}$.

• Journal of computational fluids engineering
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• v.9 no.4
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• pp.48-54
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• 2004

Vortex-shedding flows past a circular cylinder for 200≤ Re ≤ 5000 are numerically simulated with the PowerCFD code, using a finite volume method and an unstructured grid system, developed by the author. The simulation is peformed by solving the unsteady 2-D Wavier-Stokes equations with both no model and turbulence model. The resulting Reynolds number dependence of the Strouhal number and of the drag and lift coefficients is compared with both experiments and previous numerical results. It is found that, in the range of 200≤ Re ≤ 5000 the calculation method with a turbulence model is capable of producing reasonably more accurate results than that with no model for the main practically relevant parameters such as Strouhal number, drag and lift coefficients.

• Journal of computational fluids engineering
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• v.9 no.4
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• pp.41-47
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• 2004

The paper presents numerical simulations of laminar vortex-shedding flows past a circular cylinder for Re ≤ 500. The simulations are performed by solving the unsteady 2-D Navier-Stokes equations with a finite volume method using unstructured grid system. The resulting Reynolds number dependence of the Strouhal number and of the drag and lift coefficients is compared with experiments and with previous numerical results, showing good agreement. It is found that, for the truly laminar Reynolds number range the present calculation method described is capable of producing reasonably accurate results for the main practically relevant parameters such as Strouhal number, drag and lift coefficients.

• Wind and Structures
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• v.35 no.3
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• pp.157-175
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• 2022

This paper highlights the minimization of drag and lift coefficient of different types both side setback tall buildings by the multi-objective optimization technique. The present study employed 48 number both-side setback models for simulation purposes. This study adopted three variables to find the two objective functions. Setback height and setback distances from the top of building models are considered variables. The setback distances are considered between 10-40% and setback heights are within 6-72% from the top of the models. Another variable is wind angles, which are considered from 0° to 90° at 15° intervals according to the symmetry of the building models. Drag and lift coefficients according to the different wind angles are employed as the objective functions. Therefore 336 number population data are used for each objective function. Optimum models are compared with computational simulation and found good agreements of drag and lift coefficient. The design wind angle variation of the optimum models is considered for drag and lift study on the main square model. The drag and lift data of the square model are compared with the optimum models and found the optimized models are minimizing the 45-65% drag and 25-60% lift compared to the initial square model.