• Journal of Advanced Marine Engineering and Technology
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• 제14권2호
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• pp.48-65
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• 1990

Numerical solutions of the Navier-Stokes equations, governing 2-dimensional, time-dependent, viscous, incompressible fluid flow past a square cylinde in an infinite region, are presented for Reynolds numbers $10^2$, $10^3$and $10^4$. Finite-difference scheme, based on SOLA-VOF is adopted and a discretization of the convection term for irregular grid is newly suggested by altering the original nonconservation form into conservation one. Distribution of finer grids around the body reveals fairly reasonable consistency with the experimental variables : drag coefficient, lift coefficient, Strouhal number, fluctuating pressure coefficient, etc.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.614-625
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• 2004

The main purpose of this study is to get flowrate coefficient 'q' and to study characteristics of flowrate of screw pump. This study is based on Muskin's formula and depends on the computer simulation. The results of study are as follows. 1. Flowrate coefficient will reduce according to increase of inclination. The larger the pitch ratio is and the smaller the diameter ratio is, the more coefficient reduces. 2. As a rule, the coefficient increases according to reduction of the diameter ratio, but the coefficient tends to reduce when the ratio is less than 0.45. So, in actual application, it is recommended that the ratio should be above 0.45. 3. If the pitch ratio increases, the coefficient increases in case of small inclination and decreases in case of large inclination. 4. The coefficient increases according to number of windings. Especially, singles winding is not used in actual application because it has too small coefficient. 5. The coefficient decreases when the influent water level falls. Flowrate is almost zero when the water level is below $40\%$ of Filling Points.

• 수산해양기술연구
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• 제53권3호
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• pp.228-239
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• 2017

This study investigated the drag coefficient and lift coefficient of thirteen kinds of knotless nettings used for large purse seine gear. By comparing the hydrodynamic characteristics with nets of the previous study, the characteristics of this study were derived as a purse seine gear. Thirteen kinds of nettings with different length of bar (l) and diameter (d) were used in the experiment, out of which six kinds used the 30 mm in mesh size and three kinds with 40 mm. The drag coefficient ($C_d$) also increased with increasing d/l. It can be expressed as $C_d=3.71499(d/l)+0.76595$ at a current speed 0.4 m/s and $C_d=4.30324(d/l)+0.69056$ at a current speed 0.5 m/s. Compared with previous studies, drag coefficient values were similar to knotless net of similar d/l and smaller than drag coefficient of knot net. Therefore, using knotless net in a purse seine has the advantage of reducing the resistance acting on the purse seine gear.

• 한국운동역학회지
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• 제13권3호
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• pp.117-131
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• 2003

This study simulated the range of golf ball with different projection angles using a drive swing condition. For the simulation purpose, the differential equation of dynamics was induced by using Bernoulli's principle and average back spin frequency, instant velocity, and dimple of golf ball from amateur group, professional group, and Tiger Woods were chosen as the initial condition. The study result indicated that lift coefficient($C_{lift}$) relative to drag coefficient ($C_d$), 0.3 of differential equation was applied differently in terms of back spin Sequency, and when $C_{lift}$ was 0.4 for amateur, 0.5 for professional, and 0.7 for Tiger Woods the projection ranges of ball were closely matched with initial condition. With selected $C_{lift}$ and back spin frequency of initial condition, the ranges with different projection angle was measured as 193m ($13-17^{\circ}$) for amateur, 240m ($9-13^{\circ}$), professional and 273m ($9^{\circ}$)Tiger Woods, respectively. For the range in terms of back spin frequency and projection angle, the amateur group indicated relatively high spin frequency (70 RPS) and showed the maximal range (195m) with $13^{\circ}$ of projection angle. The tendency of longer range with higher projection angle was also found under the different conditions of spin frequency in this group. The professional group showed their maximal range (245m) with conditions of 60RPS of spin frequency and $9^{\circ}$ of projection angle. Their range was decreased dramatically when the spin frequency was reduced to 40-50 RPS. For Tiger Woods, the maximal range was found with 40RPS of spin frequency and the range was decreased notably when the spin frequency was above 40RPS.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1649-1660
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• 1996

The flow around a circular cylinder was controlled by an acoustic excitation issued from a thin slit along the cylinder axis. The static pressure distributions around the cylinder wall and flow characteristics in the near wake have been measured. Experiments were performed under three cases of Reynolds number, 7.8 * 10$\^$4/, 2.3 * 10$\^$5/ and 3.8 * 10$\^$5/. The effects of excitation frequency, sound pressure level and the location of the slit were examined. Data indicate that the excitation frequency and the slit location are the key parameters for controlling the separated flow. At Re$\_$d/, = 7.8 * 10$\^$4/, the drag is reduced and the lift is generated to upward direction, however, at Re$\_$d/, =2.3 * 10$\^$5/ and 3.8 * 10$\_$5/, the drag is increased and lift is generated to downward direction inversely. It is thought that the lift switching phenomenon is due to the different separation point of upper surface and lower surface on circular cylinder with respect to the flow regime which depends on the Reynolds number. Vortex shedding frequencies are different at upper side and lower side. Time-averaged velocity field shows that mean velocity vector and the points of maximum intensities are inclined to downward direction at Re$\_$d/ = 7.8 * 10$\^$4/, but are inclined to upward direction at Re$\_$d/ = 2.3 * 10$\^$5/.

• 대한기계학회논문집B
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• 제35권4호
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• pp.345-352
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• 2011

고속으로 주행하는 자동차에서 전면유리 와이퍼의 부상 현상은 와이퍼의 닦임 성능을 저해하여 운전자의 안전을 위협한다. 본 연구에서는 고속 주행 시 와이퍼가 작동하는 차량 주변의 3차원 CFD 해석을 수행하여 와이퍼의 닦임 성능 향상을 위한 방안을 모색하였다. 정확한 해석결과를 얻기 위하여 차량과 와이퍼의 자세한 형상을 모델링하였고, 해석 결과로 와이퍼의 양력계수와 항력계수를 산출하였다. 또한, 수치해석을 통하여 와이퍼 작동 각도와 후드 끝단 각도가 전면유리 와이퍼의 양력계수와 항력계수에 미치는 영향에 대하여 분석하였다.

• 한국항공운항학회지
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• 제17권4호
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• pp.8-16
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• 2009

An experimental study was carried out to investigate aerodynamic characteristics on reduced frequency of flapping wings. The half span of the wing is 28cm, and the mean chord length of wing is 10cm. In flight, the Reynolds Number range of birds is about $10^4$, and the reduced frequency during a level flight is 0.25. The experimental variables of present study were set to have similar conditions with the bird flight's one. The freestream velocities in a wind tunnel were 2.50, 3.75 and $5.00^m/s$, and the corresponding Reynolds numbers were $1.7{\times}10^4$, $2.5{\times}10^4$ and $3.3{\times}10^4$, respectively. The wing beat frequencies of an experimental model were 2, 3 and 4Hz, and the corresponding reduced frequency was decided between 0.1 and 0.5. Aerodynamic forces of an experimental flapping model were measured by using 2 axis load-cell. Inertial forces measured in a vacuum chamber were removed from measuring forces in the wind tunnel in order to acquire pure aerodynamic forces. Hall sensors and laser trigger were used to make sure the exact position of wings during the flapping motion. Results show that the ratio of downstroke in a wing beat cycle is increased as a wing beat frequency increases. The instantaneous lift coefficient is the maximum value at the end of downstroke of flapping wing model. It is found that a critical reduced frequency with large lift coefficient is existed near k=0.25.

• 한국유체기계학회 논문집
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• 제17권6호
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• pp.64-68
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• 2014

This paper is intended to provide experimental data for the design of the small VAWT(vertical axis wind turbine). Three types(lift, drag, and hybrid) of the blade of VAWT are tested with digital wind tunnel in this study. From the test, the relation of power coefficient and tip speed ratio for the blades are evaluated and compared each other depending on the blade type. Especially, the characteristics of hybrid blade which is shown to be expanded in the market without any logical data is proposed in the relation of power coefficient and tip speed ratio. It is shown that the hybrid blade can be used to make higher starting torque with trade off of degradation of power coefficient.

• Journal of Advanced Marine Engineering and Technology
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• 제26권5호
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• pp.596-606
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• 2002

The three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, PAM-FLOW based on FEM method has been applied to analyze the flow field around the high speed train which is entering into a channel. From the present study, the pressure and flow transients were calculated and analyzed. The generation of compression wave was observed ahead of train and the high pressure in the gap between the train and the tunnel was also found due to the blockage effects. It was found that abrupt fluctuation in pressure exists in the region from train nose to shoulder of train corresponding to 10％ of total length of train during tunnel entry. Computed time history of aerodynamic forces of train during tunnel entry show that drag coefficient rapidly rises and saturates at about non-dimensional time 0.31. The total increase of drag coefficient before and after tunnel entry is about 1.1%. Transient profile of lift force shows similar pattern to drag coefficient except abrupt drop after saturation and lift force in the tunnel increases 0.08% more than that before tunnel entry.

• 한국기계가공학회지
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• 제18권3호
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• pp.103-108
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• 2019

The results of the measurement of the flow-rate coefficient (Cv-value) and the analysis of a small ball valve are summarized follows. The Cv-values of 1/2-, 3/4- and 1-inch ball valves were measured using a flow-rate measurement test. The manufacturer obtained the Cv-value using a theoretical calculation method. The new experimental measurement and analysis method yielded more reliable results. In addition, the Cv value obtained through numerical analysis was almost identical the value provided by the manufacturer, which was based on experimental results. A Study on Flow Analysis results are all similar appearances as the reliability of the results.