• Title/Summary/Keyword: Attack Angle

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CAVITATION FLOW ANALYSIS OF HYDROFOIL WITH CHANGE OF ANGLE OF ATTACK (받음각 변화에 대한 수중익형의 캐비테이션 해석)

  • Kang, T.J.;Park, W.G.;Jung, C.M.
    • Journal of computational fluids engineering
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    • v.19 no.2
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    • pp.17-23
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    • 2014
  • Cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency in devices, such as propellers, pump impellers, nozzles, injectors, torpedoes, etc. Thus, the cavitating flow simulation is of practical importance for many engineering systems. In the present work, a two-phase flow solver based on the homogeneous mixture model has been developed. The solver employs an implicit preconditioning, dual time stepping algorithm in curvilinear coordinates. The flow characteristics around Clark-Y hydrofoil were calculated and then validated by comparing with the experimental data. The lift and drag coefficients with changes of angle of attack and cavitation number were obtained. The results show that cavity length and lift, drag coefficient increase with increasing angle of attack.

Missile Autopilot Design for Agile Turn Control During Boost-Phase

  • Ryu, Sun-Mee;Won, Dae-Yeon;Lee, Chang-Hun;Tahk, Min-Jea
    • International Journal of Aeronautical and Space Sciences
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    • v.12 no.4
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    • pp.365-370
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    • 2011
  • This paper presents the air-to-air missile autopilot design for a $180^{\circ}$ heading reversal maneuver during boost-phase. The missile's dynamics are linearized at a set of operating points for which angle of attack controllers are designed to cover an extended flight envelope. Then, angle of attack controllers are designed for this set of points, utilizing a pole-placement approach. The controllers' gains in the proposed configuration are computed from aerodynamic coefficients and design parameters in order to satisfy designer-chosen criteria. These design parameters are the closed-loop frequency, damping ratio, and time constant; these represent the characteristics of the control system. To cope with highly nonlinear and rapidly time varying dynamics during boost-phase, the global gain-scheduled controller is obtained by interpolating the controllers' gains over variations of the angle of attack, Mach number, and center of gravity. Simulation results show that the proposed autopilot design provides satisfactory performance and possesses good [ed: or "sufficient" or "excellent"] capabilities.

Roll-Pitch-Yaw Integrated H Controller Synthesis for High Angle-of-Attack Missiles

  • Choi, Byung-Hun;Kang, Seon-Hyeok;Kim, H. Jin;Won, Dae-Yeon;Kim, Youn-Hwan;Jun, Byung-Eul;Lee, Jin-Ik
    • International Journal of Aeronautical and Space Sciences
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    • v.9 no.1
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    • pp.66-75
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    • 2008
  • In this work, we explore the feasibility of roll-pitch-yaw integrated autopilots for high angle-of-attack missiles. An investigation of the aerodynamic characteristics of a surface-to-air missile is presented, which reveals the strong effects of cross coupling between the longitudinal and lateral dynamics. Robust control techniques based on $H_{\infty}$ synthesis are employed to design roll-pitch-yaw integrated autopilots. The performance of the proposed roll-pitch-yaw integrated controller is tested in high-fidelity nonlinear five-degree-of-freedom simulations accounting for kinematic cross-coupling effects between the lateral and longitudinal channels. Against nonlinearity and cross-coupling effects of the missile dynamics, the integrated controller demonstrates superior performance when compared with the controller designed in a decoupled manner.

A study on the characteristics of end region flow field for partially cavitating hydrofoil (익형에 발생하는 부분 캐비테이션 후연영역 유동장 특성 연구)

  • 문철진;김시영
    • Journal of Advanced Marine Engineering and Technology
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    • v.12 no.1
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    • pp.53-61
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    • 1988
  • Most of the recent for the flow field hydrofoil in partially cavitating condition are the ones which are linearized, and the problem of cavity end region for hydrofoil is not verified. This paper deals with a study on characteristics of end region flow field for partially cavitating hydrofoil by using a characteristics of shear turbulence flow and nonlinear cavity flow theory. The results obtained as follows : 1) Shear layer thickness is decreased gradually going to the end section of hydrofoil. When attack angle is large, it is appeared largely at the region of partial cavitation after its collapsing. 2) The fluctuation velocity of a second-degree relative direction have minimum value at the front of hydrofoil or at the end of hydrofoil. The difference for the validity of attack angle is appeared largely at the surrounding of .chi.$_{e}$ point. 3) The fluctuation velocity of transverse direction decrease from the maximum thickness of cavitation to the end of hydrofoil, but it undergoes largely the effect of pressure recovery. The difference is larger at the region of partial cavitation after its collapsing than at the of hydrofoil. 4) The distribution of Reynolds stress have maximum values at the region of partial cavitation after its collapsing and the end of foil, and the larger attack angle, the larger the distribution of value.e.

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Computational Flow Analysis and Drag Coefficient Research for Angle of Attack in Slocum Underwater Glider (Slocum 수중 글라이더의 유영 받음각에 대한 전산유동해석 및 항력계수 연구)

  • Park, Jeong-Woo;Lee, Jung-Woo;Choi, Young-Ho;Seo, Kap-Ho;Suh, Jin-Ho;Park, Jong-Jin
    • Journal of Ocean Engineering and Technology
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    • v.30 no.5
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    • pp.381-388
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    • 2016
  • An underwater glider makes it easy to explore a wide area with low power. However, an underwater glider is difficult to use for rapid collection, because the surfacing location cannot be predicted after a dive. Thus, simulation research is needed to predict the swimming path. In this paper, based on research, a linearized equation is derived for the drag coefficient at each angle of attack by assuming the boundary conditions for the Slocum underwater glider and performing a computational flow analysis.

Vane deployer with a hydrofoil array for enhanced lift-to-drag ratio at wide range of angle of attack (넓은 받음각 범위에서 높은 양항비를 가지는 다중 수중익 형상의 전개장치)

  • Park, Jooyeon;Park, Hyungmin
    • Journal of the Korean Society of Visualization
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    • v.17 no.2
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    • pp.25-31
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    • 2019
  • A device that consists of an array of hydrofoils (called a vane deployer) is widely used in ocean engineering. In general, the vane deployer has to spread out efficiently, which is possible by enhancing the lift-to-drag ratio. In the present study, using a computational fluid dynamics, we investigate the effect of hydrofoil arrangement on the lift-to-drag ratio to establish the condition in which a reasonable level of constant lift-to-drag ratio is achieved in a wide range of angle of attack, to avoid a degradation of the hydrodynamic performance. First, the flow around two-dimensional hydrofoil array is examined by varying the size of hydrofoil components, gap between the hydrofoils, and arrangement type. As a result, we determine the optimized hydrofoil array configuration whose lift-to-drag ratio is nearly independent on the angle of attack. Finally, a three-dimensional simulation is performed for the optimized geometry to estimate the performance of actual vane deployer.

Simulation of porous claddings using LES and URANS: A 5:1 rectangular cylinder

  • Xu, Mao;Patruno, Luca;Lo, Yuan-Lung;de Miranda, Stefano;Ubertini, Francesco
    • Wind and Structures
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    • v.35 no.1
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    • pp.67-81
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    • 2022
  • While the aerodynamics of solid bluff bodies is reasonably well-understood and methodologies for their reliable numerical simulation are available, the aerodynamics of porous bluff bodies formed by assembling perforated plates has received less attention. The topic is nevertheless of great technical interest, due to their ubiquitous presence in applications (fences, windbreaks and double skin facades to name a few). This work follows previous investigations by the authors, aimed at verifying the consistency of numerical simulations based on the explicit modelling of the perforated plates geometry and their representation by means of pressure-jumps. In this work we further expand such investigations and, contextually, we provide insight into the flow arrangement and its sensitivity to important modelling and setup configurations. To this purpose, Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Large-Eddy Simulations (LES) are performed for a 5:1 rectangular cylinder at null angle of attack. Then, using URANS, porosity and attack angle are simultaneously varied. To the authors' knowledge this is the first time in which LES are used to model a porous bluff body and compare results obtained using the explicit modelling approach to those obtained relying on pressure-jumps. Despite the flow organization often shows noticeable differences, good agreement is found between the two modelling strategies in terms of drag force.

Numerical Analysis of Non-Axisymmetric Supercavitating Flow Around a Three-Dimensional Cavitator with an Angle of Attack (받음각을 갖는 3차원 캐비테이터에서 발생하는 비축대칭 초공동 유동해석)

  • Dae-Gyu Hwang;Byoung-Kwon Ahn
    • Journal of the Society of Naval Architects of Korea
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    • v.60 no.4
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    • pp.240-247
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    • 2023
  • In this study, morphological and hydrodynamic characteristics of the non-axisymmetric supercavity generated behind a disk-shaped cavitator were examined. By extending the previous study on axisymmetric supercavitating flow based on a boundary element method, hydrodynamic forces acting under the angle of attack condition of 0 to 30 ° and shape characteristics of the supercavity were analyzed. The results revealed that increasing the angle of attack by 30 ° reduced the length and width of the cavity by about 15% and the volume by about 40 %. An empirical formula that can quantitatively estimate the geometrical characteristics and change of the cavity was derived. It is expected that this method can be used to evaluate the shape information and force characteristics of the supercavity for the control of the vehicle in a very short time compared to the viscous analysis in the initial design stage of the supercavity underwater vehicle.

Galloping characteristics of a 1000-kV UHV iced transmission line in the full range of wind attack angles

  • Lou, Wenjuan;Wu, Huihui;Wen, Zuopeng;Liang, Hongchao
    • Wind and Structures
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    • v.34 no.2
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    • pp.173-183
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    • 2022
  • The galloping of iced conductors has long been a severe threat to the safety of overhead transmission lines. Compared with normal transmission lines, the ultra-high-voltage (UHV) transmission lines are more prone to galloping, and the damage caused is more severe. To control the galloping of UHV lines, it is necessary to conduct a comprehensive analysis of galloping characteristics. In this paper, a large-span 1000-kV UHV transmission line in China is taken as a practical example where an 8-bundled conductor with D-shaped icing is adopted. Galerkin method is employed for the time history calculation. For the wind attack angle range of 0°~180°, the galloping amplitudes in vertical, horizontal, and torsional directions are calculated. Furthermore, the vibration frequencies and galloping shapes are analyzed for the most severe conditions. The results show that the wind at 0°~10° attack angles can induce large torsional displacement, and this range of attack angles is also most likely to occur in reality. The galloping with largest amplitudes in all three directions occurs at the attack angle of 170° where the incoming flow is at the non-iced side, due to the strong aerodynamic instability. In addition, with wind speed increasing, galloping modes with higher frequencies appear and make the galloping shape more complex, indicating strong nonlinear behavior. Based on the galloping amplitudes of three directions, the full range of wind attack angles are divided into five galloping regions of different severity levels. The results obtained can promote the understanding of galloping and provide a reference for the anti-galloping design of UHV transmission lines.

Study on the hydrodynamic coefficients of the nettings (망지의 유체역학적 계수에 관한 연구)

  • Song, Dae-Ho;Lee, Chun-Woo
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.45 no.1
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    • pp.34-45
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    • 2009
  • In this study, the hydrodynamic coefficients were measured using various nettings to analyze the change of drag coefficients and lift coefficients as a basic study for deriving hydrodynamic coefficients. The data on hydrodynamic force obtained from the flume tank tests were used to compare and analyze the hydrodynamic coefficients based on Reynolds number. Standardized hydrodynamic coefficients were then assumed during the analysis procedures. The hydrodynamic coefficients were measured using the 9 kinds of nettings in which had the same total projected area with different diameters and mesh-grouping ratio. These different netting systems : mesh-grouping ratio. The results of the test of nettings were as follows; First, the drag coefficients of nettings increased when the higher attack angles applied, and decreased with the increased flow speed and netting twine diameter. Second, the lift coefficients of nettings showed the increased values until the attack angle 30 degree, but decreased for the attack angle over 40 degree. Third, the hydrodynamic coefficients of netting decreased as the Reynolds number increased, and reach at slightly states in the highest numbers. Fourth, the hydrodynamic coefficients were derived from a functional formula considering attack angles and Reynolds number, and presented in the three dimensional space.