• Advances in aircraft and spacecraft science
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• v.2 no.1
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• pp.45-56
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• 2015

The attitude aerodynamic control is an important subject in the design of an aerospace plane. Usually, at high altitudes, this control is fulfilled by thrusters so that the implementation of an aerodynamic control of the vehicle has the advantage of reducing the amount of thrusters fuel to be loaded on board. In the present paper, the efficiency of a wing-flap has been evaluated considering a NACA 0010 airfoil with a trailing edge flap of length equal to 35% of the chord. Computational tests have been carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km, in the range of angle of attack 0-40 deg. and with flap deflection equal to 0, 15 and 30 deg.. Effects of the flap deflection have been quantified by the variations of the aerodynamic force and of the longitudinal moment. The shock wave-boundary layer interaction and the shock wave-shock wave interaction have been also considered. A possible interaction of the leading edge shock wave and of the shock wave arising from the vertex of the convex corner, produced on the lower surface of the airfoil when the flap is deflected, generates a shock wave whose intensity is stronger than those of the two interacting shock waves. This produces a consistent increment of pressure and heat flux on the lower surface of the flap, where a thermal protection system is required.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1051-1057
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• 2004

A numerical optimization procedure for the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer is presented. The response surface method is used as an optimization technique with Reynolds-averaged Wavier-Stokes analyses of flow and heat transfer. SST turbulence model is used as a turbulence closure. Computational results for local heat transfer rate show reasonable agreements with experimental data. The pitch-to-height ratio of the rib and rib height-to-channel height ratio are set to be 9.0 and 0.1, respectively, and width-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with weighting factor. Full-factorial experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained in the range from 0.0 to 0.1 of weighting factor.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.47-51
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• 2004

Accurate Prediction of a supersonic missile base drag continues to defy even well-rounded CFD codes. In an effort to address the accuracy and predictability of the base drags, the influence of grid system and competitive turbulence models on the base drag is analyzed. Characteristics of some turbulence models is reviewed through incompressible turbulent flow over a flat plate, and performance for the base drag prediction of several turbulence models such as Baldwin-Lomax(B-L), Spalart-Allmaras(S-A), $\kappa-\epsilon$, $\kappa-\omega$ model is assessed. When compressibility correction is injected into the S-A model, prediction accuracy of the base drag is enhanced. The NSWC wind tunnel test data are utilized for comparison of CFD and semi-empirical codes on the accuracy of base drag predictability: they are about equal, but CFD tends to perform better. It is also found that, as angle of attack of a missile with control (ins increases, even the best CFD analysis tool we have lacks the accuracy needed for the base drag prediction.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.114-123
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• 2020

A high-order potential-based panel method based on Green's theorem, with piecewise-linear dipole strength on triangular panels, is formulated for the analysis of potential flow around a three-dimensional wing. Previous low-order panel methods adopt square panels with piecewise-constant dipole strength, which results in inherent errors. Square panels can not represent a high curvature lifting body, such as propellers, since the four vertices of the square panel do not locate at the same flat plane. Moreover the piecewise-constant dipole strength induces inevitable errors due to the steps in dipole strength between adjacent panels. In this paper a high-order panel method is formulated to improve accuracy by adopting a piecewise linear dipole strength on triangular panels. Firstly, the square panels are replaced by triangular panels in order to increase the geometric accuracy in representing the shape of the object with large curvature. Next, the step difference of the dipole strength between adjacent panels is removed by adopting piecewise-linear dipole strength on the triangular panels. The calculated results by the present method is compared with analytical ones for simple non-lifting geometries, such as ellipsoid. The results for an elliptic wing with zero thickness at finite angle of attack are compared with Jordan's results. The comparison shows reasonable agrements for the both lifting and non-lifting bodies.

• Wind and Structures
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• v.29 no.6
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• pp.471-488
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• 2019

Wind pressure is a critical argument for the wind-resistant design of structures. The attempt, however, to explore the wind pressure field on buildings still encounters challenges though a large body of researches utilizing wind tunnel tests and wind field simulations were carried out, due to the difficulty in logical treatments on the scale effect and the modeling error. The full-scale measurement has not yet received sufficient attention. By performing a field measurement, the present paper systematically addresses wind pressures on the rectangular attic of a double-tower building. The spatial and temporal correlations among wind speed and wind pressures at measured points are discussed. In order to better understand the wind pressure distribution on the attic facades and its relationship against the approaching flow, a full-scale CFD simulation on the similar rectangular attic is conducted as well. Comparative studies between wind pressure coefficients and those provided in wind-load codes are carried out. It is revealed that in the case of wind attack angle being zero, the wind pressure coefficient of the cross-wind facades exposes remarkable variations along both horizontal and vertical directions; while the wind pressure coefficient of the windward facade remains stable along horizontal direction but exposes remarkable variations along vertical direction. The pattern of wind pressure coefficients, however, is not properly described in the existing wind-load codes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.10-17
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• 2003

Dynamic stability is critically required to stabilize an airship which is statically unstable. Numerical computations were performed in order to support and confirm the foced oscillation wind tunnel tests. To analyze the low-speed flow filed around the airship, a low-Mach number preconditioned method was applied. Using two computation methods, variations of the dynamic damping coefficients were examined. Numerical results show that it is dynamically stable for three directional moments, but unstable for normal or side force. It is revealed that the damping coefficients are more sensitive to the direction of the angular rate than the angle of attack or the magnitude og angular rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.879-886
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• 2004

A numerical optimization has been carried out to determine the shape of the three-dimensional channel with oblique ribs attached on both walls to enhance turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Numerical results fur heat transfer rate show good agreements with experimental data. four dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, streamwise rib distance on opposite wall to rib pitch ratio, and the attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related coefficients with a weighting factor. D-optimal method is used to determine the training points as a means of design of experiment. Sensitivity of the objective parameters to each design variable has been analyzed. And, optimal values of the design variables have been obtained in a range of the weighting factor.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.1
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• pp.25-32
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• 2013

The shape of a conventional full spade rudder has been modified to implement the Coanda effect and consequential changes in the flow characteristics are carefully examined to show the significant enhancement in the lift performance. A preliminary numerical study has been done to identify the optimum configuration of the modified rudder sections. For the purpose, chord wise locations of the jet slit and the radii of the trailing edge were varied in several ways and the changes in the lift characteristics have been observed at the various angles of attack, particularly focusing on the usefulness of the Coanda effect upon delaying the stall or increase in the circulation. Making the most use of the results so attained, full spade rudder of a VLCC has been reformed to realize the Coanda effect. A series of model experiments and numerical simulations are performed to confirm the effectiveness of the Coanda effect in improving the performance of the modified rudder. It is found that considerable enhancement in the lift performance of the rudder is plausible at any rudder angle if an optimum jet momentum is provided.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.400-400
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• 2016

자연하천에서 다양한 목적으로 설치된 수공구조물을 볼 수 있으며 대표적으로 교량의 교각을 들 수 있다. 교각 주위에서 발생하는 국부세굴은 교량붕괴의 가장 큰 원인이므로 이에 대한 연구는 필수적이다. 수리실험 또는 수치모형을 이용하여 교각주변의 국부세굴에 관한 많은 연구들이 수행되었지만 세굴인자의 특성 및 메커니즘에 대한 연구는 여전히 부족하다. 본 연구에서는 LES(large-eddy simulation)에 유사이송 및 하상변동 모형과 결합하여 2개의 원형교각 주변의 흐름 및 세굴을 수치모의 하였다. LES와 유사이송 및 하상변동 모형의 결합은 난류의 영향을 직접 모형에 고려할 수 있기 때문에 교각 주변에서 발생하는 말굽형 와 구조와 같은 복잡한 흐름에 의한 영향이 반영된다. 계산영역은 흐름방향으로 10 m, 횡 방향으로 2.4 m로 하였고, 지름(D) 0.16 m를 가지는 원형교각을 유입부로부터 2.4 m 떨어진 위치에 배치하였다. 이때 두 개 교각사이의 각은 $0^{\circ}{\sim90^{\circ}$이고 원형교각 사이의 거리는 5D로 하였다. 수치모의에 사용된 조건은 이전의 수리실험(Khosronejad et al., 2012)을 참고하여 접근평균유속은 0.25 m/s, 수심은 0.15m를 사용하였다. 수치모의는 원형교각 주변의 최대세굴심이 평형상태에 이를 때 까지 수행하였다. 접근각도 변화에 따른 원형교각 주변의 세굴과정 및 특성을 분석하였으며 최대 세굴심 결과를 Hannah(1978)의 수리실험결과와 비교하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.91-98
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• 2018

A numerical investigation of stage separation behavior of a two-body vehicle focusing on its flow characteristics is carried out. For this simulation, the separation of a booster from a vehicle is modeled using a chimera grid system and calculated with commercial code, $CFD-FASTRAN^{TM}$. Consideration of spring force, gravity and relative acceleration of a booster is the essential factor of a realistic simulation. In this study, it is validated that the booster separation time decreases with an increase in flight Mach number and angle of attack. In view of results thus far achieved, it is expected that the dynamics modeling and boundary condition set-up applied in this study will be useful for estimating safe stage separation and event sequencing of flight tests.