• Journal of Fisheries and Marine Sciences Education
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• v.24 no.1
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• pp.18-24
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• 2012

This study analyses the effects of various angles in sculling on human body lift and drag by means of computational fluid dynamics, discusses the importance of sculling and provides a basis for the development of future water safety education programmes. Study subjects were based on the mean data collected from males in the age of 20s from a survey on the anthropometric dimensions of the Koreans. Moreover, lift, drag as well as coefficient values, all of which were governed by the angle of the palm, were calculated using 3-dimentional modelling produced by computational fluid dynamics programmes i.e. CFD. Interpretations were performed via general k-${\varepsilon}$ turbulence modelling in order to determine lift, drag and coefficient values. Turbulence intensity was set to one per cent as per the figures from preceding research papers and 3-dimentional simulations were performed for a total of five different angles $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$ and $60^{\circ}$. The drag and lift values for the differing angles of the hands during sculling movement are as follows. The lift and drag values gradually increased with the increasing angle of the palm, however, the magnitude of increase for drag started to predominate lift from $45^{\circ}$ and lift gradually decreased from $60^{\circ}$. Overall, it is concluded that the optimal efficiency of sculling can be achieved at the angles $15^{\circ}$ and $30^{\circ}$, and it is anticipated that greater safety and informative education can be ensured for Life saving trainees if the results were to be applied to practical settings. However, as the study was conducted using simulation programmes which performed analyses on the collected anthropometric dimension, the obtained results cannot be made universal, which warrants furthers studies involving varied study subjects with actual measurements taken in water.

• Journal of Ocean Engineering and Technology
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• v.11 no.1
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• pp.55-64
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• 1997

A wing operating in close proximity to the ground exhibits a reduction in induced drag, which increase the lift/drag ratio. The poert-augmented ram (RAR) phenomenon involves directiing the efflux from forward mounted propulsion ststem under the wings, with the efflux nearly stagnated under the wings. In the present paper, 3 dimentional PAR was numerically studied by solving the Navier-Stokes equations. Pressure distribution and velocity vectors are calculated around the wing surface and the ground. Through the numerical simulation, Cp values and lift/drag ratio are carefully reviewed by changing the height/chord; 0.05, 0.1, 0.3 and 0.8. The shape of model is NACA 0012 with a span/chord ratio of 3.0. According to the numerical results, the relationship between lift/drag and height/chord is fairly reasonable.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.565-568
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• 2002

In the flow analysis around a bluffbody such as road vehicles, drag reduction has been of the primary concern mainly due to the effect on fuel economy. To reduce the drag, which is mostly due to the pressure difference caused by the flow separation, the location of the separation and eddy sizes are controlled. However, less attention has been given to the effect of the lift. The effect of lift may cause the driving stability problem of the vehicle at high speed white heavy downward effect of lift together with the vehicle weight may require more power to drive the vehicle forward. It is considered worthwhile to pursue the optimal design of the low drag tail shape of the MIRA model while taking the lift effect into account, even though it is considered as a reference. To this end, a commercial multi-objective optimization code, FRONTIER, Is used together with the CFD code, STAR-CD. It is hoped that the results will provide more insight into the flow field around the bluffbody as transportation means.

• 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 the Korean Society of Visualization
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• v.9 no.2
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• pp.40-47
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• 2011

Tilt-rotor aircraft can be used in various fields because they have the capabilities of the vertical take-off and landing and the high-speed cruise flight. In the present study, the flow analysis of a tilt-rotor aircraft is conducted at various tilt angles. The lift and drag forces of the tilt-rotor aircraft are obtained and the wakes by the rotor-blade are visualized. The result shows that the rotor-blade affects the lift force in a hovering mode and the main wing has an influence on the lift force in a cruise mode. Additional thrust is required at the tilt angle of around 40 degree due to the least lift force. The drag force is dependent on the rotor-blade at overall tilt angles. The minus drag force appears between the tilt angles of 90 degree and 55 degree. Also, the drag force is dramatically increased at the other tilt angles. The wake by rotor-blade affects the flow around the fuselage of the tilt-rotor aircraft at the tilt angles of 75 degree and 60 degree.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.6 no.1
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• pp.7-20
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• 1998

A reduction of induced drag is an important problem in order to save fuels. In this study, the aerodynamic characteristics of wing tip devices to reduce induced drag, such as end plate, plain ring, helical ring wing tip device, was experimentally investigated in a low speed wind tunnel. The experimental results showed that the wing model with a helical ring wing tip device reduced a induced drag and increased lift-drag ratio.

• 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.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.491-496
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• 2000

The objective of this study is to increase lift and decrease drag of an airfoil by delaying flow separation with piezo-ceramic actuators. The airfoil used is NACA 0012 and the chord length is 30cm. An experiment is performed at the freestream velocity of 15m/s at which the Reynolds number is $3{\times}10^5$. Seven rectangular actuators are attached to the airfoil surface and move up and down based on the electric signal. At the attack angle of $16^{\circ}$, the separation point is delayed downstream due to momentum addition induced by the movement of the actuators. Drag and lift are measured using an in-house 2-dimensional load cell and the surface pressures are also measured. Lift is increased by 10%, drag is reduced by 50%, and the efficiency is increased to 170%. The flow fields with and without control are visualized using the smoke-wire and tuft techniques.

• The KSFM Journal of Fluid Machinery
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• v.15 no.5
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• pp.54-59
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• 2012

In order to have the high efficiency of aircraft wing and to improve the energy efficiency in field of eco-friendly transportation, the performance characteristics of the aircraft wing were studied with the change of lift to drag ratio through the CFD analysis. The design process was focused on generating the high lift force and low drag force as the lift to drag ratio was increased. In this paper, various dimple patterns were numerically designed to investigate the flow characteristics. Hexagon-and circle-shaped dimples, dimple distance and position were changed as the artificial conditions. The numerical analyses were conducted by using the commercial code, ANSYS CFX. Numerical results dependent on the turbulence intensity and lift to drag ratio distribution were graphically depicted for various dimple patterns.

• 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.