• Title/Summary/Keyword: 충격면적

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Preliminary Design for Axisymmetric Supersonic Inlet using Conical Flow Solution and Optimization Technique (원추 유동 해와 최적화 기법을 이용한 축대칭 초음속 흡입구의 예비 설계)

  • 정석영
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.9
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    • pp.11-19
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    • 2006
  • Design program was developed to determine the external shape of the supersonic axisymmetric inlet by combining conical flow solver and approximation technique of conical shock with gradient-based optimization algorithm. Inlet designs were carried out under various operation conditions through optimization with respectively two object functions which consist of pressure recovery and cowl drag and with constraints about shock position, cowl shape, and minimum throat area. New object function consisting of pressure recovery and drag of the external cowl was proposed and the optimized shapes from new object function were compared to the ones from the old object function which maximize only the pressure recovery. Through computations of inviscid and turbulent flow, was tested performance of the design program and performance estimated in design program agreed well with computation results for inlets designed under various flight conditions.

Investigation on optimum cavitation-erosion protection potential of anodized 5083-H321 Al alloy in sea water (양극산화 처리된 5083-H321 알루미늄 합금의 해수 내 캐비테이션-침식 방지를 위한 최적 방식전위 규명)

  • Yang, Ye-Jin;Jang, Seok-Gi;Kim, Seong-Jong
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2016.11a
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    • pp.143-143
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    • 2016
  • 알루미늄 합금은 내구성과 내식성이 우수할 뿐만 아니라 다양한 표면개질을 통해 그 표면 특성을 더욱 향상시킬 수 있다. 특히 Al-Mg계 5083-H321 Al 합금의 경우 가공성 및 용접성이 우수하여 선체 재료로 널리 이용되는데, 이는 선체중량의 경량화가 가능하여 연료비 절감과 빠른 선속 등 다양한 이점을 지니기 때문이다. 그러나 선속의 고속화에 따라 선체에 가해지는 유체충격이 증가하고 정압 저하에 기인하여 캐비테이션-침식 손상이 증가할 뿐만 아니라 해수환경 특성 상염소이온의 존재로 부식이 가속화되는 등 침식 및 부식의 시너지효과로 손상은 크게 증가한다. 이에 대한 방지대책으로 다양한 표면개질 기법이 제안되고 있으나 강한 충격압이 동반된 캐비테이션 침식-부식 복합 손상 환경에서는 표면처리만으로는 불가능할 수 있다. 따라서 본 연구에서는 양극산화된 5083-H321을 대상으로 캐비테이션 환경 하에서 일정 전위를 인가하여 침식-부식 손상이 최소화되는 최적전위를 규명하고자 한다. 이를 위해 먼저 분극 실험을 통해 재료의 전기화학적 거동을 바탕으로 임의의 전위를 선정하고 해당 전위를 인가한 상태에서 캐비테이션 실험을 실시하였다. 이때 분극실험과 캐비테이션-전기화학 복합실험 모두 $25^{\circ}C$의 해수에서 실시하였으며, 전기화학적 분극실험은 유효면적이 $3.24cm^2$인 시편에 2 mV/s의 분극속도로 0 ~ -3 V 까지 인가하였고, Ag/AgCl 기준전극과 백금대극을 사용하였다. 캐비테이션-전기화학 복합 실험은 정전위를 인가한 상태에서 $30{\mu}m$의 진폭으로 20분간 실시하였으며, 혼팁과 시험편 사이의 거리는 1 mm로 일정하게 유지하였다. 실험 후 표면 손상의 정량적 분석을 위해 인가된 전위별 전류밀도를 비교하고, 무게감소량을 측정하였으며, 손상특성 분석을 위해 3D현미경과 주사전자현미경(SEM)을 통해 표면을 분석하였다.

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Movement and Deposition Characteristics of Debris Flow According to Rheological Factors (유동학적 인자에 따른 토석류의 이동 및 퇴적 특성)

  • Lee, Mi-Ji;Kim, Yun-Tae
    • Journal of the Korean Geotechnical Society
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    • v.29 no.5
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    • pp.19-27
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    • 2013
  • Most of the landslides induced by rainfall in summer rainy season appear in the type of debris flow. Debris flow gives a lot of economic losses and human casualties due to high moving velocity and volume of debris flow. In order to analyze movement and deposition characteristics of debris flow, numerical analysis using FLO-2D program was conducted with various viscosities and yield stresses. As a result of numerical analysis, velocity and runout distance of debris flow decreased as its viscosity increased due to resisting force between particles of debris flow. Consequently, flow depth of debris flow increased and impact force decreased. Yield stress of debris flow affected its initiation and deposition characteristics. As yield stress increased, runout distance of debris flow decreased and its impact force increased. Based on the results of numerical analysis, it was found that velocity of debris flow mainly depended on viscosity, while deposition characteristics (runout distance, deposition width, deposition area) of debris flow depended on both viscosity and yield stress.

A Numerical Study on Effects of Displacement of a Variable Area Nozzle on Flow and Thrust in a Jet Engine (가변노즐의 변위가 제트 엔진의 유동 및 추력특성에 미치는 영향에 관한 수치해석)

  • Park, Junho;Sohn, Chae Hoon;Park, Dong Chang
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.5
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    • pp.1-9
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    • 2013
  • Variable area nozzle, where both throat and exit area vary, is required for optimal expansion and optimal nozzle shape upon operation of after-burner. Steady-state and transient analyses are carried out for each condition with and without afterburner operation and as a function of the location of the nozzle flap. Effects of that nozzle displacement on flow and thrust characteristics are analyzed from numerical results. With variable area nozzle adopted, the combustion field is variable in time, leading to periodically variable thrust. For off-design conditions, flow separation shows up due to over expansion at the flap tips and shock wave does in the nozzle due to under expansion. The undesirable phenomena can be solved by control of variable area nozzle.

Thrust and Aerodynamic Load Characteristics of an Internal Pintle Thruster (노즐 목 내부형 핀틀추력기의 추력 및 공력하중 특성)

  • Choi, Junsub;Kim, Dongyeon;Huh, Hwanil
    • Journal of the Korean Society of Propulsion Engineers
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    • v.21 no.3
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    • pp.1-9
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    • 2017
  • Numerical computations are performed to investigate the effect of pintle stroke on the performance of an internal pintle thruster. Results show that the thrust control ratio was less than 2% and the aerodynamic load ratio was 22% as the pintle stroke increased. The flow past the nozzle throat rapidly expanding because of the shape of the pintle, and a shock wave was generated. Particularly, at the pintle stroke distance of 4 and 5 mm, the shock wave hit the wall of the nozzle, results in peeling bubbles. Depending on the altitude, the thrust increased and the aerodynamic load decreased, but the difference was as small as 1.5%. In the presence of the bore, the reduction of the pintle tip area resulted in a decrease in aerodynamic load.

Investigation of Effect of Shape of Pintle on Drag and Thrust Variation (핀틀 형상에 따른 추력 및 항력 변화 연구)

  • Park, Jong-Ho;Kang, Min-Ho;Kim, Joung-Keun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.3
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    • pp.237-243
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    • 2010
  • In this study, the effect of the shape of a pintle(obstacle) on thrust-modulation performance and drag in a pintle rocket was investigated by a cold flow test and by computational fluid dynamics. Pintle movement caused a monotonic increase in the chamber pressure. Thrust generated by the pressure distribution on the pintle body was linearly changed to the chamber pressure, and this thrust was greater than that generated by the nozzle-wall pressure distribution. Because the shock pattern in the nozzle changes with the shape of the pintle body and pressure ratio, the thrust generated by the nozzle-wall pressure is not directly affected by chamber pressure. The drag due to the pintle(obstacle) can be minimized for a fully linear pintle shape, regardless of chamber pressure.

A study on the pintle-tip shapes effect of nozzle flow using cold-flow test (핀틀 형상이 노즐 유동에 미치는 영향에 대한 실험적 연구)

  • Kim, Joung-Keun;Park, Jong-Ho;Lee, Jong-Hoon;Jeon, Min-Kyung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.38 no.10
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    • pp.985-991
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    • 2010
  • The objective of this work was to investigate the pintle-tip shape effect on nozzle flow and thrust by cold flow test. When nozzle throat area was decreased by pintle movement, chamber pressure was increased monotonously but thrust was increased differently according to every pintle-tip shape. At the same chamber pressure and nozzle throat area, thrust of convex pintle-tip shape was mostly larger than that of concave one. Nozzle wall pressure distribution and magnitude of pintle-tip load depended on the pintle-tip shape, pintle position and nozzle throat area.

A Study on the Fabrication and Characteristics of Continuous W-Cu FGM by Spark Plasma Sintering (방전플라즈마소결법에 의한 W-Cu 연속경사기능재료의 제조와 특성에 관한 연구)

  • 신철균;강태훈;권영순;김지순;김환태;석명진
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2003.03a
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    • pp.217-217
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    • 2003
  • W-Cu 합금은 우수한 전기적, 열적 특성으로 인하여 열소산재료(Heat sink)로 많이 응용되고 있다. 첨단 전자부품 이외에도 핵융합로의 Diverter가 그 예로서, 내부는 고강도와 고융점의 특성을 요구하는 반면, 외부는 높은 열전도성을 필요로 한다. 그래서 동일한 조성의 일반적인 W-Cu 합금보다 W과 Cu의 조성이 점차적으로 변화하는 경사기능재료(Functionally Graded Materials)가 냉각효율이 클 것으로 기대된다. 현재, W-Cu FGM에 대한 많은 연구가 진행되고 있지만, 그 조성이 연속적으로 변화하는 W-Cu FGM에 대한 연구는 전무한 실정이다 본 연구에서는 방전플라즈마 소결장치(Spark Plasma Sintering System)와 용침고정을 이용하여 연속적인 조성변화를 갖는 W-Cu FGM을 제조하고 그 특성에 관해 분석하고자 하였다. 소결체가 밀도 변화를 갖게 되도록 제작한 특수 경사기능 몰드에 W분말을 장입한 후, 15㎬의 압력하에서 SPS를 이용하여 W소결체를 제조하였다. 제조된 W소결체는 수평관상로에서 수소분위기 하에 Cu 용침을 실시하여 W-Cu FGM을 제조하였다 SEM을 이용한 각 위치별 조직관찰과 Image Analyzer를 이용한 W과 Cu의 면적비, 그리고 비커스경도계에 의한 경도 측정을 실시하였다. 또 열기계적 분석기를 이용하여 측정된 선팽창률로부터 열팽창계수를 구하였다. 80$0^{\circ}C$에서 ?칭하는 반복적인 싸이클을 통해 열충격시험을 실시하였고, Laser flash method로 열확산계수를 측정하였다.

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Concentration Effects on Improved Mechanical Properties of Chopped Kenaf Fiber Filled Polypropylene Composite (케냐프섬유로 강화된 PP복합재료내의 섬유의 함량이 기계적특성 향상에 미치는 효과)

  • Oh, Jeong-Seok;Lee, Seong-Hoon;Kim, Kwang-Jea
    • Elastomers and Composites
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    • v.46 no.2
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    • pp.125-131
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    • 2011
  • The effects of chopped kenaf fiber concentration on mechanical property of polypropylene (PP) composite are investigated. The addition of kenaf increased the tensile strength, flexural modulus, impact strength, specific gravity, and HDT, while decreased the elongation%, flexural strength, and melt flow index. The increase of mechanical properties is due to increased surface area contacting between fiber and polymer matrix and fiber-fiber interaction. Volatile extractives in the kenaf seemed to decrease the interfacial adhesion between kenaf surface and PP.

Preliminary Design of Movable Ramjet Intake (가변 초음속 흡입구 기본설계)

  • Lee, Kyung-Jae;Kang, Sang-Hun;Lee, Yang-Ji;Yang, Soo-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.05a
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    • pp.207-210
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    • 2008
  • In this study, one type of ramjet intake were designed for the flight condition of Mach number 4 and numerical analysis was performed. In order to widen the flight envelope range (Mach number $2{\sim}6$), movable intake concept was applied. The central body was designed so that the capture area ratio which is one of most important factors of ramjet intake design could be adjusted. And various types of cowl and movable insert part of shell were designed in order to control throat area which could increase total pressure recovery. The numerical results showed that the designed ramjet intake could be applied in various flights Mach number.

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