• Title, Summary, Keyword: Angle Of Attack

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An Experimental Study on Effect of Angle of Attack on Elevator Control Force for Underwater Vehicle with Separate Fixed Fins (별도의 고정타를 갖는 수중운동체 승강타의 제어력에 미치는 받음각의 영향에 대한 실험적 연구)

  • Park, CJeong-Hoon;Shin, Myung-Sub;Choi, Jae-Yeop;Hwang, Jong-Hyun;Shin, Young-Hun;Kim, Yeon-Gyu
    • Journal of Ocean Engineering and Technology
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    • v.30 no.4
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    • pp.243-252
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    • 2016
  • Conventionally, the static angle of attack and static elevator tests are carried out separately to estimate hydrodynamic stability derivatives of underwater vehicles. However, it is difficult to verify the interaction between the angle of attack and elevator angle in such cases. In this study, we perform a static elevator with angle of attack test where both the angle of attack and elevator angle are varied simultaneously. The experimental results show that the angle of attack has an influence on the elevator control force and that this tendency is dependent on the sense in which the angle of attack and elevator angle are varied. We predict level flight performance using hydrodynamic derivatives estimated through this experiment. The predictions considering the effect of angle of attack show good agreement with trials conducted in the open sea.

The Study of Prediction Method of Cavity Shape Considering Both Gravity Effect and Angle of Attack of Cavitator (중력효과 및 캐비테이터 받음각 고려 공동 형상 예측기법 연구)

  • Kim, Minjae;Yi, Jongju;Kim, Sunbum
    • Journal of the Korea Institute of Military Science and Technology
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    • v.21 no.2
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    • pp.180-187
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    • 2018
  • In this study, we develop a prediction method of cavity shape taking gravity effect and angle of attack of cavitator into consideration simultaneously. Logvinovich's theoretical formulas are superimposed to predict the change of cavity centerline due to both gravity effect and angle of attack of cavitator. It is found that as the angle of attack of cavitator increases, the gravity effect is weakened due to decrease in cavity volume, and even in case of the same angle of attack, cavity shape changes in different ways depending on whether the angle of attack of cavitator is positive or negative. We conclude that cavity shapes are largely affected by the angle of attack of cavitator, and the gravity effect and angle of attack of cavitator should be considered at the same time for the prediction of cavity shape.

A Numerical Study on the Flowfield around a NACA 0021 Airfoil at Angles of Attack (NACA 0021 익형 유동장의 수치해석적 연구)

  • Kim, Sang-Dug
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.24 no.4
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    • pp.20-25
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    • 2016
  • A primary benefit of flight at high angle-of-attack conditions is to be able to reduce the speed of flight and maneuvers, which can enhance the capability of sensing and obstacle avoidance for a small UAV. The flight at high angle-of-attack conditions, however, is easy to be beyond stall which is characterized by substantial flow separation over an airfoil. Current numerical analysis was conducted on the capabilities of three representative turbulence models to predict the aerodynamic characteristics of a typical airfoil at angle-of-attack conditions. The investigation shows that these turbulence models provide good comparison with experimental data for attached flow at moderate angle-of-attack conditions. Calculation by current turbulence models are, however, not appropriate at high angle-of-attack conditions with flow separation.

Kill Probability Analysis Based on the Relation between Final Angle of Attack and Impact Angle of a Guided Anti-tank Missile (대전차유도무기의 종말 받음각 및 입사각의 상관관계에 의한 표적 파괴율 분석)

  • Jeong, Dong-Gil
    • Journal of the Korea Institute of Military Science and Technology
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    • v.13 no.4
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    • pp.520-527
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    • 2010
  • The kill probability of a missile depends on guidance error, warhead performance, and etc. In this paper, we analyzed the kill probability of anti-tank missile in a new approach. Under the condition that the missile hit the target, we studied the effect of angle of attack and impact angle. High impact angle increase the probability that the missile hits the upper armour which is relatively weaker, while high angle of attack at the impact instant decreases the effectiveness of the jet induced by the warhead. We proposed a way to increase the capability of penetration by analyzing the interrelation between impact angle and angle of attack.

Interaction between Turbulent Boundary Layer and Wake behind an Elliptic Cylinder at Incidence (앙각을 가진 타원형 실린더 후류와 평판 경계층의 상호작용에 대한 연구)

  • Choi, Jae-Ho;Lee, Sang-Joon
    • Proceedings of the KSME Conference
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    • pp.465-471
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    • 2000
  • The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angel of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder according to the direction of the angle of attack.

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ANALYSIS OF UNSTEADY OSCILLATING FLOW AROUND TWO DIMENSIONAL AIRFOIL AT HIGH ANGLE OF ATTACK (고받음각 2차원 에어포일 주위의 비정상 유동의 진동 특성에 관한 연구)

  • Yoo, J.K.;Kim, J.S.
    • Journal of computational fluids engineering
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    • v.18 no.1
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    • pp.1-6
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    • 2013
  • Missile and fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 50 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure, entropy distribution, etc. are analyzed according to the angle of attack. The results of average lift coefficients are compared with other results according to the angle of attack. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. The primary and secondary oscillating frequencies are analyzed by the effects of these unsteady aerodynamic characteristics.

Unsteady Aerodynamic characteristics at High Angle of Attack around Two Dimensional NACA0012 Airfoil (고 받음각 2차원 NACA0012 에어포일 주위의 비정상 공기역학적 특성)

  • Yoo, Jae-Kyeong;Kim, Jae-Soo
    • 한국전산유체공학회:학술대회논문집
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    • pp.414-419
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    • 2011
  • Missile am fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 60 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure distribution, etc. are analyzed according to the angle of attack. The results at a low angle of attack are compared with other results before a stall condition. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution on the airfoil surface, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

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Development of Servo Type Angle-of-Attack Sensor for UAV (무인항공기용 서보형 받음각센서 개발)

  • Park, Mi-Hyun;Kim, Sung-Su;Ryoo, Chang-Kyung;Choi, Kee-Young;Park, Choon-Bae
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.5
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    • pp.511-517
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    • 2009
  • A servo type angle of attack sensor using the null-seeking method is designed and its characteristics are analyzed in this study. Angle-of-attack in the null-seeking method is given by the probe rotation angle with respect to the body reference line when pressure difference measured in two holes on the probe becomes zero. This method provides highly accurate and uniform angle-of-attack measurements over all range. Hence, this kind of angle-of-attack sensor is adequate for unmanned aerial vehicles(UAVs). In this paper, we first analyze the requirements for developing angle-of-attack sensors. And the servo type angle-of-attack sensor is then designed and fabricated. The on-board angle-of-attack calculation algorithm is also developed. Finally, the characteristics of the developed angle-of-attack sensor are identified through MATLAB Simulink and wind tunnel tests.

앞전에서의 팽창파를 이용한 양항비의 개선에 대한 연구

  • Yun, Yeong-Jun
    • Proceeding of EDISON Challenge
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    • pp.19-22
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    • 2016
  • Leading edge thrust is generally caused by passing air flow from lower to upper surface and it is required to have sufficient angle of attack for notable leading edge thrust. To produce leading edge thrust at low angle of attack, utilizing expansion wave accompanying low pressure is able to be a solution. Fore structure changes the direction of flow, and this flow passes the projected edge. As a result, from a perspective of the edge, it is able to have high angle of attack, and artificial expansion wave is generated. This concept shows 9.48% increase of L/D in inviscid flow, at Mach number 1.3 and angle of attack $1^{\circ}$ in maximum, and this model shows the 3.98% of increasement at angle of attack $2^{\circ}$. Although advantage of the artificial expansion wave decreased as angle of attack increase, it shows the possibility of aerodynamical improvement with artificial expansion wave.

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Numerical Analysis of Flow Characteristics around 3D Supersonic Inlet at Various Angle of Attack (받음각이 있는 3차원 초음속 흡입구 주위의 유동진동 해석)

  • Kim, J.;Hong, W.;Kim, C.
    • 한국전산유체공학회:학술대회논문집
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    • pp.218-224
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    • 2011
  • A supersonic inlet at angle of attack has anti-symmetric pressure distribution, and it can make flow instability and structural problem. In this study, numerical analysis of three-dimensional inviscid flow was conducted under various throttle ratio and angle of attack conditions. Throttle ratio was defined as the ratio of the exit area to the smallest cross section area at inlet, and the ratio is controlled from 0 to 2.42. At various angle of attack, the characteristics of steady and unsteady flow around supersonic inlet is observed under different throttling ratios. From these results, pressure recovery curves and pressure history curves were plotted by post processing. Using pressure history data, FFT analysis is also carried out. Through these processes, it shows the tendency of pressure distribution anti-symmetricity and changing dominant frequency as increasing angle of attack.

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