• Title/Summary/Keyword: induced drag

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A Study on the Total Drag Estimation for the Aircraft Conceptual Design (항공기 개념설계를 위한 전체항력 예측에 관한 연구)

  • 김상진;전권수;이재우
    • Journal of the Korea Institute of Military Science and Technology
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    • v.2 no.2
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    • pp.70-82
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    • 1999
  • During the aircraft conceptual design stage, rapid aerodynamic analyses over various configurations are required. Hence, empirical and analytical methods play important roles in predicting the aero-dynamic characteristics. In this study, total drag estimation method based on empirical and analytical approaches is developed. By comparing with the results of the wind tunnel experiment and existing prediction methods, it is demonstrated that the developed method is accurate and useful in predicting total drag for the whole Mach number range.

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Drag Reduction Design for a Long-endurance Electric Powered UAV

  • Jin, Wonjin;Lee, Yung-Gyo
    • International Journal of Aeronautical and Space Sciences
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    • v.16 no.2
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    • pp.311-324
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    • 2015
  • This study presents computational analyses for low-drag aerodynamic design that are applied to modify a long-endurance UAV. EAV-2 is a test-bed for a hybrid electric power system (fuel cell and solar cell) that was developed by the Korean Aerospace Research Institute (KARI) for use in future long-endurance UAVs. The computational investigation focuses on designing a wing with a reduced drag since this is the main contributor of the aerodynamic drag. The airfoil and wing aspect ratio of the least drag are defined, the fuselage configuration is modified, and raked wingtips are implemented to further reduce the profile and induced drag of EAV-2. The results indicate that the total drag was reduced by 54% relative to EAV-1, which was a small-sized version that was previously developed. In addition, static stabilities can be achieved in the longitudinal and lateral-directional by this low-drag configuration. A long-endurance flight test of 22 hours proves that the low-drag design for EAV-2 is effective and that the average power consumption is lower than the objective cruise powerof 200 Watts.

Feasibility Analysis on Wind Turbine Embedded to Highway Median Strip - Consideration on Vehicle Drag Coefficient (고속도로 중앙분리대형 풍력발전 타당성 분석 - 차량 저항계수 관점에서)

  • Yoon, Seong-Wook;Jeon, Wan-Ho;Kim, Hyun-Goo
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.06a
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    • pp.536-538
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    • 2009
  • In recent day, many people are interested in wind resource for generation of electric power. Especially, it is made assessment the possibility of generation of electric power by wind resource originated from running cars and buses in downtown or highway. Moreover bus, driven in the exclusive lane, is focused on possibility of generation electric power on highway because median strip makes fast flow way between bus body and median strip and a pattern will appear in the flow way like drag coefficient. But nobody can guess whether the induced flow will increase or decrease and estimate amount of change of drag coefficient. Solving drag coefficient of bus running highway is the point of this paper. To solve this problem, we use the CFD method. The model is a bus simplified without mirror and gates. In order to assess result, the flow analysis surrounding the bus on the flat road where median strip is not installed has been compared with road with median strip. Solving condition is that the driving highway and median strip are running with 100km/h (27.8m/s).

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Drag Reduction Induced by Increased Kinematic Viscosity of Nanofluids Containing Carbon Nanotubes in A Horizontal Tube (카본나노튜브 나노유체의 동점성계수 증가로 인한 관내 유동에서의 항력 감소)

  • Yu, Jiwon;Jung, Se Kwon;Choi, Mansoo
    • Particle and aerosol research
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    • v.9 no.4
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    • pp.271-277
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    • 2013
  • This article reports the drag reduction phenomenon of aqueous suspensions containing carbon nanotubes (CNTs) flowing through horizontal tubes. Stable nanofluids were prepared by using a surfactant. It is found that the drag forces of CNT nanofluids were reduced at specific flow conditions compared to the base fluid. It is found that the friction factor of CNT nanofluids was reduced up to approximately 30 % by using CNT nanofluids. Increased kinematic viscosities of CNT nanofluids are suggested to the key factors that cause the drag reduction phenomenon. In addition, transition from laminar to turbulent flow is observed to be delayed when CNT nanofluids flow in a horizontal tube, meaning that drag reduction occurs at higher flow rates, that is, at higher Reynolds numbers.

Experimental Study on the Flow-Induced Vibration of Inclinced Circular Cylinders in Uniform Flow (균일 유동장내에서의 경사진 원형실린더의 유동유기진동 특성 연구)

  • Jung, Tae-Young;Hong, Sup;Moon, Seok-Jun;Ham, Il-Bae;Lee, Hun-Gon
    • Journal of KSNVE
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    • v.5 no.3
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    • pp.303-311
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    • 1995
  • Tests on flow-induced vibration of inclined cylinders in uniform flow were performed in the cavitation tunnel at the Korea Instituteof Machinery and Metals. The test program was intended to investigate flow-induced vibration characteristic of the cylinders with three different inclined angles of 10$^\circ$, 20$^\circ$ and 30$^\circ$ and to estimate the fluid force coefficients acting on the cylinders. Important observations are as follows: 1) Numal drag is dominant compared with viscous drag for the inclined angle over 20.deg. and it has the value from 1.7 to 2.0 as was observed by other researchers. 2) Lift force coefficient has large value at the lock-in range determined by 4$\Theta/f_nD$<8. Measured maximum lift force coefficients at the inclined angle of 30.$^\circ$ and 20$^\circ$ were 0.9 and 0.4 respectively.

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An Experimental Study on the Aerodynamic Characteristics of a Streamline-designed High-speed Bus (유선형 고속주행 버스의 공력특성에 관한 실험 연구)

  • Kim, Chul-Ho;Lee, Seung-Hyun
    • Transactions of the Korean Society of Automotive Engineers
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    • v.24 no.2
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    • pp.198-204
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    • 2016
  • In this study, a wind tunnel test was conducted to measure the aerodynamic characteristics of a streamline-designed high-speed bus with the change of wind direction and speed and the result is compared with the aerodynamic performance of a commercialized high-speed bus model (Model-0) manufactured by Zyle Daewoo Bus Corp. Aerodynamic performance of the existing rear-spoiler was tested to prove its aerodynamic effect on the test model bus. From the study, it was found that 24.6 % of the total drag of the original bus model (Model-0) was reduced on the streamline-designed model bus(model-1) without the rear-spoiler but only 14.3 % of the total drag was reduced with the spoiler on the streamlined model bus. It means that the rear spoiler does not work properly with the streamlined model bus (model-1) and should be noted that an optimum design of a rear-spoiler of a vehicle is important to reduce the induced pressure drag and increase the driving stability of a vehicle against yaw motion. The experimental outcome was also compared to the previous numerical research result to evaluate the reliability of the numerical algorithm of the aerodynamic performance analysis of a vehicle. The error rate (%) of the numerical result to the experimental output is about 5.4 % and it is due to the simplified body configuration of the numerical model bus. The drag increases at the higher yaw angle because the transparent frontal area of the model vehicle increases and the downward force increases with the yaw angle as well. It has a positive effect to the driving stability of the vehicle but the moderated downward force should be kept for the fuel economy of a vehicle.

Forces induced by flows past two nearby circular cylinders (두 개의 원형 실린더에 작용하는 유체력)

  • Lee, Kyong-Jun;Yang, Kyung-Soo;Yoon, Dong-Hyeog
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2845-2850
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    • 2007
  • Flow-induced forces on two identical nearby circular cylinders immersed in the cross flow at Re =100 were numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of flow-induced forces are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for drag coefficient and lift coefficient for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

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Forces Induced by Flows Past Two Nearby Circular Cylinders (두 개의 원형 실린더에 작용하는 유체력)

  • Lee, Kyong-Jun;Yoon, Dong-Hyeog;Yang, Kyung-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.9
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    • pp.754-763
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    • 2007
  • Flow-induced forces on two identical nearby circular cylinders immersed in the cross flow at Re=100 were numerically studied. We consider all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of flow-induced forces are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of force coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for drag coefficient and lift coefficient for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate flow-induced forces on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.

The Evaluation of Dynamic Load for the Cone Type Venturi Flow meter (원추형 벤튜리 유량계에 관한 동하중 평가)

  • 김중권;장경영;조남오
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.140-144
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    • 1997
  • Although the cone type venturi flow meter is superior to another differential pressure type flow meter in precision, the venturi is installed at the pipe as an L beam, so that the dynamic load due to drag force and flow-induced force is generated in the flow meter. In this paper we propose a methodology to evaluate this dynamic load directly by using stain-gages attached on the venturi and we discuss about the dynamic characteristics on the basis of flow-induced vibration theory.

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A Study on Perception and Reaction of Ground Effect during Landing of Large Airplanes (대형기 착륙과정의 지면효과에 대한 인식과 대응에 관한 연구)

  • Moon, Bong-Sup;Choi, Youn-Chul
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.26 no.1
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    • pp.1-9
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    • 2018
  • Ground effect includes a reduction of induced drag, increase of lift, and nose-down moment during landing. These phenomena, occurring late in the landing maneuver, are considered to be of little significance because they tend to counteract and/or compensate in this respect. Even though it is unlikely to affect any flare profile variations appreciably, some pilots have reversed perception about such phenomenon and overestimate during landing. It is becoming a negative factor and is making an adverse effect on landing maneuver. This study examines the perception of ground effect of large aircraft pilots, reviews literature regarding ground effect, and makes suggestions that pilots can correctly recognize and respond to the effect during landing flare maneuvers.