• Title/Summary/Keyword: drag

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Prediction of Three Dimensional Turbulent flows around a MIRA Vehicle Model (MIRA Vehicle Model 주위의 3차원 난류유동 예측)

  • 명현국;진은주
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.5
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    • pp.86-96
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    • 1998
  • A numerical study has been carried out of three-dimensional turbulent flows around a MIRA reference vehicle model both with and without wheels in computation. Two convective difference schemes with two k-$\varepsilon$ turbulence models are evaluated for the performance such as drag coefficient, velocity and pressure fields. Pressure coefficients along the surfaces of the model are compared with experimental data. The drag coefficient, the velocity and pressure fields are found to change considerably with the adopted finite difference schemes. Drag forces computed in the various regions of the model indicate that design change decisions should not rely just on the total drag and that local flow structures are important. The results also indicate that the RNG model with the QUICK scheme predicts fairly well the tendency of velocity and pressure fields and gives more reliable drag coefficient rather than the other cases.

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A Study on the Prediction and Measurement of Afterbody Drag for a Supersonic Aircraft (초음속 전투기 후방동체 항력 예측 및 측정에 관한 연구)

  • Kim, Won-Cheol
    • Journal of the Korea Institute of Military Science and Technology
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    • v.12 no.6
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    • pp.711-718
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    • 2009
  • During the preliminary design phase of a supersonic aircraft, it is necessary to evaluate many potential engine/airframe combinations to determine the best solution to given set of mission requirements. And it is very important to establish a methodology to predict precisely afterbody drag so that accurate engine installed performance can be estimated. It was carried out in this paper to establish a methodology to predict afterbody drag of F-15K supersonic aircraft based on IMS(Integral Mean Slope) methodology, acquire afterbody drag data and compare its calculated data with the test data acquired from the wind tunnel test data based on 4.7% model scale. The comparison results showed good agreement between the calculated data and test data and it was found that the methodology described here to predict and test afterbody drag is acceptable.

Aerodynamic Performance Improvement by Divergent Trailing Edge Modification to a Supercritical Airfoil

  • Yoo, Neung-Soo
    • Journal of Mechanical Science and Technology
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    • v.15 no.10
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    • pp.1434-1441
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    • 2001
  • A computational study has been performed to determine the effects of divergent trailing edge (DTE) modification to a supercritical airfoil in transonic flow field. For this, the computational result with the original DLBA 186 supercritical airfoil was compared to that of the modified DLBA 283. A wavier-Stokes code, Fluent 5. 1, was used with Spalart-Allmaras's one-equation turbulence model. Results in this study showed that the reduction in drag due to the DTE modification is associated with weakened shock and delayed shock appearance. The decrease in drag due to the DTE modification is greater than the increase in base drag. The effect of the recirculating flow region on lift increase was also observed. An airfoil with DTE modification achieved the same lift coefficient at a lower angle of attack while giving a lower drag coefficient. Thus, the lift-to-drag ratio increases in transonic flow conditions compared to the original airfoil. The lift coefficient increases considerably whereas the lift slope increases just a little due to DTE modification.

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IMPROIVING THE PERFORMANCE OF STREAMLINED BOATS BY ENAMEL COATING

  • V.M.Salokhe;D.Gee-Clough;N, Birewar
    • Proceedings of the Korean Society for Agricultural Machinery Conference
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    • 1993.10a
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    • pp.148-157
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    • 1993
  • A study was conducted to evaluate the effect of enamel coating on boat hull drag. The results were compared with drag required for varnished uncoated boats. Models of rice barge and fishing boat were used in this study. The speed range of 0.6 to 1.5㎧ at different loads varying from 6 to 9 kg for rice barge and 4.6 to 6.4kg for fishing boats were used during testing. The total weight of the coated and uncoated boats were kept the same. It was observed that the drag force required by the coated boats was less than identical uncoated ones at all speeds and loads. For both uncoated and coated the drag required increased with speed. The maximum recorded reductions in drag were 26% for the rice barge and 28% for the fishing boat model.

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Simulation of Repulsive Type Thrust Magnetic Bearing using Eddy Current (와전류를 이용한 반발식 추력 마그네틱 베어링의 시뮬레이션)

  • 유제환;임윤철;이상조
    • Tribology and Lubricants
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    • v.11 no.1
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    • pp.20-26
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    • 1995
  • Most magnetic bearings are based on the attractive force between the magnets and ferrous materials. One of the disadvantages of such attractive type magnetic bearings is the instability so that an active control device is necessary to operate bearing successfully. In this study a repulsive type magnetic bearing is analyzed which uses eddy current as a force source. The load capacities are analyzed for the various gap sizes, the rotor velocities and the frequencies of current supplied to electromagnet. Analytic Results show that as the gap size decreases, the levitation and drag forces increase, while the number of poles increasqs, the drag force decreases in the higher linear velocity region. Experimental results show that as the gap size decreases the levitation and the drag force increase, and as the velocity of rotor increases, the drag is larger than the levitation force up to certain velocity. But after that, the levitation is larger than the drag force. As the frequency of the current increases the levitation and drag decreases while the thickness of rotor gets thicker the forces decrease because of increase in eddy current loss.

Repetitive Periodic Motion Planning and Directional Drag Optimization of Underwater Articulated Robotic Arms

  • Jun Bong-Huan;Lee Jihong;Lee Pan-Mook
    • International Journal of Control, Automation, and Systems
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    • v.4 no.1
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    • pp.42-52
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    • 2006
  • In order to utilize hydrodynamic drag force on articulated robots moving in an underwater environment, an optimum motion planning procedure is proposed. The drag force acting on cylindrical underwater arms is modeled and a directional drag measure is defined as a quantitative measure of reaction force in a specific direction in a workspace. A repetitive trajectory planning method is formulated from the general point-to-point trajectory planning method. In order to globally optimize the parameters of repetitive trajectories under inequality constraints, a 2-level optimization scheme is proposed, which adopts the genetic algorithm (GA) as the 1st level optimization and sequential quadratic programming (SQP) as the 2nd level optimization. To verify the validity of the proposed method, optimization examples of periodic motion planning with the simple two-link planner robot are also presented in this paper.

Experimental Investigation of Drag Reduction by Polymer Additives (중합제 첨가에 의한 항력 감소 효과에 관한 실험적 연구)

  • 성형진;위장우;권순홍;전호환
    • Journal of Ocean Engineering and Technology
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    • v.16 no.4
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    • pp.1-6
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    • 2002
  • Experimental investigation of drag reduction by adding a polymer additive(polyacrylamid, N-401P) into water is carried out in a Circular Water Channel. The effect of viscosity, surface roughness and degradation as a function of running time is also measured with varying the concentration of polymer additives(20ppm,100ppm) and Reynolds numbers. Near and far wakes past a circular cylinder are observed by LDV. Drag forces are measured with a strain-gaged device. The experimental results show that around 5%-30% of drag reduction with the polymer solution are observed. The larger effects of drag reduction can be found at low range of Reynolds number, more roughened surface cylinder. The effect of polymer solution for near wakes is larger than for far wakes.

Active Control Methods for Drag Reduction in Flow over Bluff Bodies (뭉툭한 물체 주위 유동에서 항력 감소를 위한 능동 제어 방법)

  • Choi Haecheon
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.11-16
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    • 2002
  • In this paper, we present two successful results from active controls of flows over a circular cylinder and a sphere for drag reduction. The Reynolds number range considered for the flow over a circular cylinder is 40-3900 based on the free-stream velocity and cylinder diameter, whereas for the flow over a sphere it is $10^{5}$ based on the free-stream velocity and sphere diameter. The successful active control methods are a distributed (spatially periodic) forcing and a high-frequency (time periodic) forcing. With these control methods, the mean drag and lift fluctuations decrease and vortical structures are significantly modified. For example, the time-periodic forcing at a high frequency (larger than 20 times the vortex shedding frequency) produces $50{\%}$ drag reduction for the flow over a sphere at $Re=10^{5}$. The distributed forcing applied to the flow over a circular cylinder results in a significant drag reduction at all the Reynolds numbers investigated.

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Application of Matched Asymptotic Expansion for Designing a Leading Edge of Super-cavitating Foil

  • Yim, Bo-hyun
    • Journal of Ship and Ocean Technology
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    • v.1 no.2
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    • pp.11-18
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    • 1997
  • The leading edge of a low-drag super-cavitating foil has been made to be thick enough by using a point drag which is supposed to be a linear model of the Kirchhoff lamina. In the present paper, the relation between the point drag and the Kirchhoff lamina is made clear by analyzing the cavity drag of both models and the leading edge radius of the point drag model and the lamina thickness of Kirchhoff\`s profile K. The matched asymptotic expansion is effectively made use of in designing a practical super-cavitating fool which is not only of low drag but also structurally sound. Also it has a distinct leading edge cavity separation point. The cavity foil shapes of trans-cavitating propeller blade sections designed by present method are shown.

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Reduction of Steady-State Error Using Estimation for Re-Entry Trajectory (추정을 이용한 재진입 궤적의 정상상태 오차감소)

  • 박수홍;이대우
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2001.11a
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    • pp.130-134
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    • 2001
  • In the re-entry control system, errors apt to induce because the time derivative of drag acceleration is analytically estimated. Still more, the difficulty of estimation of the exact drag coefficient in hypersonic velocity and the nun-reality of the scale height cause a steady-state drag error. This paper proposes the additional method of the disturbance observer. This reduces the steady-state drag error according to the following series. First, this method estimates a error in drag acceleration time derivative by the analytic calculation and then creates the new drag acceleration time derivative using the estimated error. The performance of the re-entry control system is verified about 32 reference trajectories.

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