• 한국전산유체공학회지
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• 제18권1호
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• pp.28-35
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• 2013

Behavior of the side force generated at high angles of attack by two ogive-cylinder bodies of revolution with nose fineness ratio of 2.3 (B1) and 3.5 (B2) and the effect of a strip placed close the nose tip of each body (B1S and B2S) are analyzed through the wind tunnel test at ReD=200,000 and a=42~60 deg. The side force generated by B1 is increased by placing a strip. The side force generated by B2 is in the starboard direction and its magnitude is higher than that of the B1S. The effect of the strips with various dimensions placed on B2 is investigated. It is found that the 4-layer strip placed on the starboard reversed the direction of the side force into port direction. It is confirmed by numerical simulations that the strip promotes the flow separation and increases the average pressure on the side where it is placed and consequently produces the side force in the corresponding direction.

• International Journal of Aeronautical and Space Sciences
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• 제13권4호
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• pp.428-434
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• 2012

Missiles suffer from flight instability problems at high angles of attack, since vortex flow over a fuselage cause lateral force to the body. To overcome this problem at a high angle of attack, the development of a real time vortex controller is needed. In this paper, Proper Orthogonal Decomposition (POD) and feedback controllers are developed for real time vortex control. The POD method is one of the most well known techniques for modeling low order models that represent the original full-order model. An adaptive control algorithm is used for real time control.

• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.8-18
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• 2015

A numerical simulation for a nonslender BWB UCAV configuration with a rounded leading edge and span of 1.0 m was performed to analyze its aerodynamic characteristics. Numerical results were compared with experimental data obtained at a free stream velocity of 50 m/s and at angles of attack from -4 to $26^{\circ}$. The Reynolds number, based on the mean chord length, is $1.25{\times}106$. 3D multi-block hexahedral grids are used to guarantee good grid quality and to efficiently resolve the boundary layer. Menter's shear stress transport model and two transition models (${\gamma}-Re_{\theta}$ model and ${\gamma}$ model) were used to assess the effect of the laminar/turbulent transition on the flow characteristics. Aerodynamic coefficients, such as drag, lift, and the pitching moment, were compared with experimental data. Drag and lift coefficients of the UCAV were predicted well while the pitching moment coefficient was underpredicted at high angles of attack and influenced strongly by the selected turbulent models. After assessing the pressure distribution, skin friction lines and velocity field around UCAV configuration, it was found that the transition effect should be considered in the prediction of aerodynamic characteristics of vortical flow fields.

• Wind and Structures
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• 제20권2호
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• pp.327-347
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• 2015

This paper investigates the effects of Reynolds number (Re) on the aerodynamic characteristics of a twin-deck bridge. A 1:36 scale sectional model of a twin girder bridge was tested using the Wall of Wind (WOW) open jet wind tunnel facility at Florida International University (FIU). Static tests were performed on the model, instrumented with pressure taps and load cells, at high wind speeds with Re ranging from $1.3{\times}10^6$ to $6.1{\times}10^6$ based on the section width. Results show that the section was almost insensitive to Re when pitched to negative angles of attack. However, mean and fluctuating pressure distributions changed noticeably for zero and positive wind angles of attack while testing at different Re regimes. The pressure results suggested that with the Re increase, a larger separation bubble formed on the bottom surface of the upstream girder accompanied with a narrower wake region. As a result, drag coefficient decreased mildly and negative lift coefficient increased. Flow modification due to the Re increase also helped in distributing forces more equally between the two girders. The bare deck section was found to be prone to vortex shedding with limited dependence on the Re. Based on the observations, vortex mitigation devices attached to the bottom surface were effective in inhibiting vortex shedding, particularly at lower Re regime.

• 한국항공우주학회지
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• 제33권3호
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• pp.26-31
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• 2005

미사일 형상의 공력특성을 효율적으로 계산하는 문제는 예비설계 단계에서 아주 중요하다. 본 연구에서는 반 실험적 기법에 기초한 Missile DATCOM 계열 코드를 이용하여 공력특성에 관한 계산을 수행하였다. 코드의 정확도와 신뢰도를 점검하기 위해, 고앙각 아음속 유동과 중간 정도의 받음각을 갖는 초음속 유동장 해석에 적용하였다. 실험이나 다른 연구자의 결과와 비교적 정성적으로 일치하는 예측결과를 얻을 수 있었다. 마지막으로 캐나드와 자유롭게 회전하는 꼬리날개를 갖는 보다 복잡한 미사일 유동장 해석에 적용하였다.

• 한국항공우주학회지
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• 제30권1호
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• pp.1-8
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• 2002

자유류 속도가 40 m/sec 이고 날개의 뿌리시위에 기준한 레이놀즈수가 1.76${\times}$10$^6$인 상태에서 옆미끄럼이 삼각 날개 와류에 미치는 영향을 실험적으로 연구하였다. 받음각 범위는 16$^{\circ}$에서부터 28$^{\circ}$까지 이었으며 옆미끄럼각은 0$^{\circ}$, -10$^{\circ}$, 그리고 -20$^{\circ}$이었다. 옆미끄럼각은 바람쪽과 바람 반대쪽 와류 모두의 강도를 감소시키고, 바람쪽 와류의 붕괴를 촉진시킴이 관찰되었다. 옆미끄럼각 -10$^{\circ}$에서 바람 반대쪽의 와류는 받음각이 증가함에 따라 그 강도가 증가하였다. 이와 같은 옆미끄럼 조건에서 날개 와류의 비대칭적인 발달과 붕괴는 삼각 날개의 롤링모멘트를 어느 특정한 높은 받음각에서 급격히 바뀌게 할 수 있으며, 이는 일종의 롤링 모멘트 불안정성으로 간주할 수 있다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.387-390
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• 2006

Numerical study has been conducted in two dimensions about a NACA0012 airfoil with an oscillating microflap on the surface. We show that this microflap is effective in controlling the unsteady stall at high angles of attack. We solve the compressible Navier-Stokes equations for the Reynolds numbers with an extensible chimera grid fitted to the oscillatory microflap. For turbulent calculation, we adopt the SST $k-{\omega}$ model. We investigate the parametric effect of angle of attacks, Reynolds number, and the location where the microflap is installed.

• International Journal of Control, Automation, and Systems
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• 제2권4호
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• pp.494-500
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• 2004

The wing rock phenomenon is a high angle of attack aerodynamic motion manifested by limit cycle roll oscillations. Experimental studies reveal that direct control and manipulation of leading edge vortices, through the use of 'blowing' techniques is effective in the suppression of wing rock. This paper presents the design of a robust controller for the experimental implementation of one such 'blowing' technique - recessed angle spanwise blowing (RASB), to achieve wing rock suppression over a range of operating conditions. The robust controller employs Takagi - Sugeno fuzzy system, which is fine-tuned by experimental simulations. Performance of the controller is assessed by real-time wind tunnel experiments with an 80 degree swept back delta wing. Robustness is demonstrated by the suppression of wing rock at a range of angles of attack and free stream velocities. Numerical simulation results are used to further substantiate the experimental findings.

• Wind and Structures
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• 제4권5호
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• pp.367-382
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• 2001

Wind tunnel tests were conducted on a model of deck section from the Ting Kau cable stayed bridge. The purpose of the tests was to determine the set of aerodynamic derivatives conventionally used to describe the motion-induced forces arising from the wind flow, and to investigate the stability of the deck under different conditions of turbulence and angle of attack. The study shows that except for large negative angles of attack the deck section itself is stable up to a high wind speed, and that when instability does occur it is essentially a single degree of freedom (torsional) flutter.

• Wind and Structures
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• 제32권4호
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• pp.293-308
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• 2021

For the past three decades a significant amount of research has been conducted on bridge flutter. Wind tunnel tests for a 2000 m class twin-box suspension bridge have revealed that a twin-box deck carrying 4 m tall 50% open area ratio wind screens at the deck edges achieved higher critical wind speeds for onset of flutter than a similar deck without wind screens. A result at odds with the well-known behavior for the mono-box deck. The wind tunnel tests also revealed that the critical flutter wind speed increased if the bridge deck assumed a nose-up twist relative to horizontal when exposed to high wind speeds - a phenomenon termed the "nose-up" effect. Static wind tunnel tests of this twin-box cross section revealed a positive moment coefficient at 0° angle of attack as well as a positive moment slope, ensuring that the elastically supported deck would always meet the mean wind flow at ever increasing mean angles of attack for increasing wind speeds. The aerodynamic action of the wind screens on the twin-box bridge girder is believed to create the observed nose-up aerodynamic moment at 0° angle of attack. The present paper reviews the findings of the wind tunnel tests with a view to gain physical insight into the "nose-up" effect and to establish a theoretical model based on numerical simulations allowing flutter predictions for the twin-box bridge girder.