• Journal of the Society of Naval Architects of Korea
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• v.52 no.4
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• pp.305-314
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• 2015

In this paper, a numerical analysis is carried out to study the drag of conical cavitators, supercavity generation devices for the high-speed underwater vehicle. The realizable k-∊ turbulence model and the Schnerr-Sauer cavitation model are applied to calculate steady-state supercavitating flows around cones of various cone angles. The calculated drags of the cones are decomposed of the pressure and the friction parts and their dependency on the geometry and the flow conditions have been analyzed. It is confirmed that the pressure drag coefficients of the cones can be estimated by a simple function of both the cone angle and the cavitation number while the friction drag coefficients approximately by well-known empirical formulas, e.g., Schults-Grunow's for the drag of the flat plate. Finally a practical method for estimating the total drags of supercavitating cones is suggested, which can be useful consequently for the design of conical cavitaors.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.43-46
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• 2004

Numerical analysis for pressure drag on boattail afterbodies have been studied by Mach number, boattail angle and length ratio of body diameter and base diameter using CFD-FASTRAN that the commercial external flow CFD code. The numerical results have been compared with the experimental data that have been shown pressure drag reduction and supersonic turbulent flow characteristics for boattail afterbodies. And the prediction equation tot boattail base drag has been made by the numerical results about Mach number and boattail configuration parameters.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.577-580
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• 2002

In this paper, the pumping performance of the disk-type drag pump which works in the outlet pressure range from 4 to 0.001 Torr is studied experimentally. The pumping characteristics of various drag pumps are performed. The inlet pressures are measured for various outlet pressures of the test pump. The flow-meter method is adopted to calculate the pumping speed. Compression ratios and pumping speeds for the nitrogen gas are measured. The present experimental data show the leak-limited value of the compression ratio in the molecular transition region. The rotational speed of the pump is 24,000rpm. The inlet pressures are measured for various outlet pressures of the test pump. The ultimate Pressures for zero throughput are measured for three-stage, two-stage and single-stage disk-type, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.8
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• pp.655-661
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• 2012

In this study, aerodynamic drag of a bearingless rotor hub was predicted by computational fluid dynamics methodology using unstructured overset mixed meshes. The calculated results showed that the drag due to pressure forces rather than the viscous drag act as a major factor on both the fuselage and rotor hub, and the drag acting on the torque tube accounted for the largest portion in the hub drag. It was also found the hub drag accounted for 39 ~ 41% of the fuselage drag. Finally, the result confirmed the drag of the designed rotor hub satisfied the requirement of the aerodynamic hub drag by comparing with the drag trend of developed helicopter.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.1093-1097
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• 1995

A micro ion drag pump with planar electrodes on a glass substrate is fabricated and tested. the pump consisted of a 2- dimensional electrode pair array is driven by DC voltage using unipolar conduction. Ethy alcohol is pumped in both directions, and the flow rate and the pressure are measured, in channels of depth 100 .mu m or 200 .mu. m and width fixed at 3mm. It is found that the pump could be fabricated easily and at lower cost than the micro ion drag pumps previously investigated.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.4
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• pp.90-96
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• 1992

The effect of base cavities on the drag of a simplified tractor-trailor model for Re=4.1*10$^{5}$ is investigated experimentally. Three different types of base cavities are studied in this work. They are solid-wall, slitted-wall, and slotted-wall cavities. Slotted-wall cavity is found to be most effective for drag reduction. A maximum of 11% reduction in the zero-yaw drag coefficient is achieved with the slotted wall cavity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.542-547
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• 2004

The objective of this study is 0 estimate wind pressure acting on soundproof tunnel and noise reduction through the tunnel. For the purpose various shape of scale models were prepared and drag forces acting on each models were measured in wind tunnel. And numerical simulation was performed to confirm experimental results. As a result the lowest drag force coefficient of 0.59 was obtained in the case of arch roof shape model. Noise reduction through soundproof tunnel was simulated by using ray tracing method according to various open ratio of its roof area.

• Journal of Mechanical Science and Technology
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• v.15 no.3
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• pp.384-391
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• 2001

The aerodynamic effects of a 3-dimensional Wing in Ground Effect (WIG) which moves above the free surface has been numerically investigated via finite difference techniques. The air flow field around a WIG is analyzed by a Marker & Cell (MAC) based method, and the interactions between WIG and the free surface are studied by the pressure distributions on the free surface. Waves are generated by the surface pressure distribution, and a Navier-Stokes solver has been employed, to include the nonlinearities in the free surface conditions. The pressure values Cp and lift/drag ratio are reviewed by changing the height/chord ratio. In the present computations a NACA0012 airfoil with a span/chord ratio of 3.0 are treated. Through computational results, it is confirmed that the free surface can be treated as a rigid wavy wall.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.132-138
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• 2003

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car with the operation speed of 180km/h. The results of aerodynamic analysis for two leading car models which one is expressed with lineal beauty and the other is with curvaceous beauty are compared with each other and they offer the proposal of modification for two models in order to decrease the drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• Wind and Structures
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• v.22 no.5
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• pp.573-594
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• 2016

Simultaneous pressure measurements on 2D square prisms with various corner modifications were performed in uniform flow with low turbulence level, and the testing Reynolds numbers varied from $1.0{\times}10^5$ to $4.8{\times}10^5$. Experimental models were a square prism, three chamfered-corner square prisms (B/D=5%, 10%, and 15%, where B is the chamfered corner dimension and D is the cross-sectional dimension), and six rounded-corner square prisms (R/D =5%, 10%, 15%, 20%, 30%, and 40%, where R is the corner radius). Experimental results of drag coefficients, wind pressure distributions, power spectra of aerodynamic force coefficients, and Strouhal numbers are presented. Ten models are divided into various categories according to the variations of mean drag coefficients with Reynolds number. The mean drag coefficients of models with $B/D{\leq}15%$ and $R/D{\leq}15%$ are unaffected by the Reynolds number. On the contrary, the mean drag coefficients of models with R/D=20%, 30%, and 40% are obviously dependent on Reynolds number. Wind pressure distributions around each model are analyzed according to the categorized results.The influence mechanisms of corner modifications on the aerodynamic characteristics of the square prism are revealed from the perspective of flow around the model, which can be obtained by analyzing the local pressures acting on the model surface.