• International Journal of Aeronautical and Space Sciences
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• 제14권1호
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• pp.46-57
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• 2013

Flutter stability and buffeting response have been the topics of most concern in the design state of long-span suspension bridges. Among approaches towards the aerodynamic stability, the aerodynamic-based control method which uses control surfaces to generate forces counteracting the unstable excitations has shown to be promising. This study focused on the mechanically controlled system using flaps; two flaps were attached on both sides of a bridge deck and were driven by the motions of the bridge deck. When the flaps moved, the overall cross section of the bridge deck containing these flaps was continuously changing. As a consequence, the aerodynamic forces also changed. The efficiency of the control was studied through the numerical simulation and experimental investigations. The values of quasi-steady forces, together with the experimental aerodynamic force coefficients, were proposed in the simulation. The results showed that the passive flap control can, with appropriate motion of the flaps, solve the aerodynamic instability. The efficiency of the flap control on the full span of a simple suspension bridge was also carried out. The mode-by-mode technique was applied for the investigation. The results revealed that the efficiency of the flap control relates to the mode number, the installed location of the flap, and the flap length.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.383-388
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• 2004

This paper presents the aerodynamic coefficient modeling with a new model structure explored by Least Squares using Modulating Function Technique (LS/MFT) for an F-16XL airplane using wind tunnel data supplied by NASA/LRC. A new model structure for aerodynamic coefficient was proposed, one that considered all possible combination terms of angle of attack ${\alpha}$(t) and ${\alpha}$(t) given number of harmonics K, and was compared with Pearson's model, which has the same number of parameters as the new model. Our new model harmonic results show better agreement with the physical data than Pearson's model. The number of harmonics in the model was extended to 6 and its parameters were estimated by LS/MFT. The model output of lift coefficient with K=6 correspond reasonably well with the physical data. In particular, the estimation performances of four aerodynamic coefficients were greatly improved at high frequency by considering all harmonics included in the input${\alpha}$(t), and by using the new model. In addition, the importance of each parameter in the model was analyzed by parameter reduction errors. Moreover, the estimation of three parameters, i.e., amplitude, phase and frequency, for a pure sinusoid and a finite sum of sinusoids- using LS/MFT is investigated.

• Wind and Structures
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• 제25권5호
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• pp.475-492
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• 2017

Inclined and yawed circular cylinder is an essential element in the widespread range of structures. As one of the applications, cables on bridges were reported to have the possibility of suffering a kind of large amplitude vibration called dry galloping. In order to have a detailed understanding of the aerodynamics related to dry galloping, this study carried out a set of wind tunnel tests for the inclined and yawed circular cylinders. The aerodynamic coefficients of circular cylinders with three surface configurations, including smooth, dimpled pattern and helical fillet are tested using the force balance under a wide range of inclination and yaw angles in the wind tunnel. The Reynolds number ranges from $2{\times}10^5$ to $7{\times}10^5$ during the test. The influence of turbulence intensity on the drag and lift coefficients is corrected. The effects of inclination angle yaw angle and surface configurations on the aerodynamic coefficients are discussed. Adopting the existed the quasi-steady model, the nondimensional aerodynamic damping parameters for the cylinders with three kinds of surface configurations are evaluated. It is found that surface with helical fillet or dimpled pattern have the potential to suppress the dry galloping, while the latter one is more effective.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2707-2720
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• 1996

The aerodynamic design of the two-stages of centrifugal compressors in an 1.2MW industrial gas turbine is completed with the application of numerical analyses. The final shape of an intake, the axial guide vanes and a return channel is determined using several interactions between design and two-dimensional turbulent flow analysis, focused on the minimum loss of internal flows. The one-dimensional turbulent flow analysis, focused on the minimum loss of internal flows. The one-dimensional design and prediction of aerodynamic performances for the compressors are performed by two different methods; one is a method with conventional loss models, and the other a method with the two-zone model. The combination methods of the Betzier curves generate three-dimensional geometric shapes of impeller blades which are to be checked with a careful change of aerodynamic blade loadings. The impeller design is finally completed by the applications of three-dimensional compressible turbulent flow solvers, and the effect of minor change of design of the second-stage channel diffuser is also studied. All the aerodynamic design results are soon to the verified by component performance tests of prototype centrifugal compressors.

• 한국전산유체공학회지
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• 제8권2호
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• pp.24-32
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• 2003

In this work, we propose a new idea of flapping airfoil design for optimal aerodynamic performance from detailed computational investigations of flow physics. Generally, flapping motion which is combined with pitching and plunging motion of airfoil, leads to complex flow features such as leading edge separation and vortex street. As it is well known, the mechanism of thrust generation of flapping airfoil is based on inverse Karman-vortex street. This vortex street induces jet-like flow field at the rear region of trailing edge and then generates thrust. The leading edge separation vortex can also play an important role with its aerodynamic performances. The flapping airfoil introduces an alternative propulsive way instead of the current inefficient propulsive system such as a propeller in the low Reynolds number flow. Thrust coefficient and propulsive efficiency are the two major parameters in the design of flapping airfoil as propulsive system. Through numerous computations, we found the specific physical flow phenomenon which governed the aerodynamic characteristics in flapping airfoil. Based on this physical insight, we could come up with a new kind of airfoil of tadpole-shaped and more enhanced aerodynamic performance.

• 말소리와 음성과학
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• 제5권1호
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• pp.19-26
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• 2013

The aerodynamic characteristics (subglottal pressure (Ps) and mean airflow rate (MFR)), fundamental frequency (Fo), intensity (I), vocal efficiency (VE), and closed quotient (CQ) were compared during a sustained vowel /o/ sound under three conditions: in a comfortable loudness and pitch level (condition 1), in a maximum loudness level with a fixed pitch (condition 2), and in a maximum loudness level without a fixed pitch (condition 3). Also, multiple regression analyses were done to measure the aerodynamic characteristics affect on the VE and the CQ in each condition. The results showed the Fo, Ps, MFR, VE, and CQ increased as I increased with and without fixed pitch. Most notably, VE in condition 3 was the highest of all the conditions, but CQ was not very high. By the results of multiple regression analysis, VE was significantly affected by I and Ps in all conditions; Fo was the other main key for affecting VE in high pitch. However, none of the aerodynamic characteristics significantly affected CQ. As I increases, Fo should be increased by increasing Ps and VE. Therefore, researchers should consider and specify an a priori to Fo, Ps, and I when measuring VE to examine the complex and delicate vocal mechanism.

• 한국수소및신에너지학회논문집
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• 제28권1호
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• pp.113-119
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• 2017

An investigation on aerodynamic performance of a highly-loaded axial fan has been conducted to find the effects of tip injection and casing groove on aerodynamic performance in this study. Three-dimensional Reynolds-averaged Navier-Stokes equations with $k-{\varepsilon}$ turbulence model were used to analyze the fluid flow in the fan with Fluid-Structure Interaction (FSI) analysis. The hexahedral grid was used to construct computational domain, and the grid dependency test drew the optimal grid system. FSI analysis was also carried out to predict the deformation of rotor and stator blades, and the effect of deformation on the aerodynamic performance of axial fan was analyzed compared to the performance predicted without FSI analysis.

• 한국항공우주학회지
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• 제33권5호
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• pp.9-17
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• 2005

헬리콥터 초기 설계 단계에서는 형상 변화에 따른 공력 성능 변화를 예측하여 최적의 형상을 결정한다. 덮개꼬리로터에서는 공력성능 개선을 위해 블레이드와 덮개사이의 끝단간극, 블레이드 평면형, 그리고 블레이드 배치의 최적화가 필요하다. 본 연구에서는 비정렬 격자에 기초한 비점성 압축성 로터 유동 해석 코드를 이용하여 설계 초기 기본형상의 덮개꼬리로터에 대해 끝단간극, 블레이드 평면형, 그리고 블레이드 배치 등의 형상변화에 따른 공력 성능을 예측하고 그 특성을 파악하였다.

• 한국항공우주학회지
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• 제36권5호
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• pp.420-427
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• 2008

접힌 공력면이 전개하는 운동을 모사하기 위하여 전개 운동 방정식을 수립하고 공력면에 작용하는 모멘트 등을 모델링하였다. 공력에 의한 롤 모멘트는 정적 롤 모멘트와 감쇠 모멘트로 이루어져 있으며 정적 롤 모멘트는 전개 하중 측정을 위한 풍동 시험을 통하여 획득한 정적 롤 모멘트 계수로부터 계산된다. 롤 감쇠 계수는 패널법을 이용한 수치 해석을 통하여 산출되었는데 전개 각속도로부터 유발된 받음각에 상응하는 변위각을 공력면에 적용하여 수치해석을 하였다. 공력면 형상에 적용한 변위각은 회전 중심으로부터 공력면 끝단까지 선형적으로 증가하며 회전 중심에서는 변위가 없다. 롤 감쇠 계수는 전개 각속도에 따른 롤 모멘트 계수의 변화율로 계산되며 공력조건과 전개각의 함수이고 전개 각속도에 대해서는 일정하다고 가정하였다. 롤 감쇠를 포함하여 모사된 공력면의 전개 모사는 시험과 비교하여 유사한 결과를 보여주었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.25-32
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• 2005

The aerodynamic loads at the blade hub and the drive shaft for 1MW horizontal axis wind turbine are calculated numerically. The geometric shape of the blade such as chord length and twist angle can be obtained fran the aerodynamic optimization procedure. Various airfoil data, that is thick airfoils at hub side and thin airfoils at tip side, are distributed along the spanwise direction of the rotor blade. Under the wind data fulfilling design load cases based on the IEC61400-1, all of the shear forces, bending moments at the hub and the low speed shaft of the drive train are obtained by using the FAST code. It shows that shear forces and bending moments have a periodic. trend. These oscillating aerodynamic loads will lead to the fatigue problem at both of the hub and drive train From the load analysis the maximum shear forces and bending moments are generated when wind turbine generator system operates in the case of the extreme speed wind condition.