• Title/Summary/Keyword: 비정상 충격

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Study of The Unsteady Weak Shock Propagating through a Pipe Bend (곡관 내부를 전파하는 약한 비정상 충격파에 관한 연구)

  • Kim, H.S.;Kim, H.D.
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.456-461
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    • 2001
  • This paper depicts the weak shock wave propagating inside some kinds of pipe bends. Computational work is to solve the two-dimensional, compressible, unsteady Euler Equations. The second-order TVD scheme is employed to discretize the governing equations. For the computations, the incident normal shock wave is assumed at the entrance of the pipe bend, and its Mach number is changed between 1.1 and 1.7. The turning angle and radius of the curvature of the pipe bend are changed to investigate the effects on the shock wave structure. The present computational results clearly show the shock wave reflection and diffraction occurring in the pipe bend. In particular, the vortex generation, which occurs at the edge of the bend, and its shedding mechanism are discussed in details.

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램제트 엔진 흡입구의 점성 유동장 수치계산

  • 강호철;신동신
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2002.04a
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    • pp.59-59
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    • 2002
  • 램제트 추진기관은 압축과정을 별도의 부품 없이 형상에 의해서 감속하여 연소 압력비를 얻는다. 따라서 구동 마하수와 형상에 의해 흡입과정의 압축 효율이 결정된다. 설계점은 충분한 유량을 확보 할 수 있는 유량과 충격파 각을 조절하여 전압력 손실을 줄이도록 고려되어야 한다. 또한 연소가 일어나면 연소실 압력이 배압으로 작용하고 비행시에 받음각은 변하므로 이에 따른 성능 분석도 고려 되어야 할 사항이다. 본 연구는 국내에서 실험한 형상에 대해 수치계산을 수행하여 코드의 검증과 아울러 램제트 유동장의 수치적 시뮬레이션도 설계단계에서 하나의 도구로 이용할 수 있음을 보여준다. 실험에서는 배압 조건을 얻기 위해 유동 블록키지를 유로 내에 두어 상응하는 배압을 얻었지만 본 계산에서는 압력 경계조건을 직접 사용하였다. 유동이 비정상 특성을 가지므로 시간 정확도를 이차로 가지도록 이중시간 전진법을 사용하였다. 사용한 압력비는 충격파가 카울 끝에 닿는 임계상태에 가까운 12, 13, 14에 대해 계산을 수행하였고 부스터모드로 흡입구 끝이 막혀 있다가 램제트 모드로 바뀌어 연소실 압력이 위의 압력비라고 가정할 때의 비정상 천이 과정을 계산해 보았다. 본 계산은 흡입구 부분만을 떼어놓고 적절한 가정 하에 수행되었지만 연소실 내부도 비정상 특성을 가지므로 흡입구와 연소실을 동시에 같이 계산해야한다. 추후에 전체적인 계산을 진행하기 위한 전 단계로 흡입구 계산만을 수행하여 실험과 잘 일치하는 계산 결과를 얻었고 전체 계산을 위한 연구는 진행 중에 있다.

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Numerical Simulation of the Experimental Investigation of the Two Dimensional Ram Accelerator Combustion Flow Field (이차원 램 가속기 연소 유동장의 실험적 연구의 수치 모사)

  • 최정열;정인석;윤영빈
    • Journal of the Korean Society of Propulsion Engineers
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    • v.1 no.1
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    • pp.8-23
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    • 1997
  • Steady and unsteady numerical simulations are conducted for the comparison with the experiments performed to investigate the ram accelerator flow field by using an expansion tube facility in Stanford University. Wavier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state numerical simulation shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$$O_2$$17N_2$ fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$$O_2$$12N_2$ mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. From the result of unsteady numerical simulation, the experimental result seems to be an instantaneous state during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.

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Effect of Shock Waves on Dynamic Stability of Transonic Missiles (천음속 미사일의 동안정성에 대한 충격파 영향)

  • Park, Su-Hyeong;Gwon, Jang-Hyeok;Heo, Gi-Hun;Byeon, U-Sik
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.30 no.2
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    • pp.12-20
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    • 2002
  • Three dimentional unsteady Euler equations are solved and an integration method is presented to predict the dynamic stability derivatives of transonic missiles. Results for the Basic Finner model are compared with several experimental data to vaildate the prediction capability of the present method. The variations of dynamic stability derivatives are discussed with respect to angle of attack, Mach number, and rotation rate. Results show that shock waves between fins enhance the pitch-damping characteristics in transonic region. Results also imply that the Euler equations can give the damping coefficients with comparable accuracy.

Numerical study on the interaction between unsteady compression and unsteady expansion wave (비정상 압축파와 비정상 팽창파의 간섭에 관한 수치해석적 연구)

  • Kim, Hui-Dong;Setoguchi, Toshiaki
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.11
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    • pp.1413-1421
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    • 1997
  • A new control method to alleviate the impulsive noise at the exit of high-speed railway tunnel was applied to the compression wave at the entrance of the tunnel. This method uses the interaction phenomenon of unsteady expansion wave and unsteady compression wave. Unsteady expansion wave was assumed to be made instantaneously by the simple theory of shock tube. Total Variation Diminishing method was employed to solve the axisymmetric unsteady compressible flow field with a specified compression wave. Numerical results show that the maximum pressure gradient of the propagating compression wave decreases with increase of the wave length of the unsteady expansion wave. It is found that the impulsive noise reduction can be obtained when the unsteady expansion wave with a large wave length is emitted just before the train enters the tunnel. The present results give the possibility to reduce the impulsive noise at the exit of tunnel.

Investigation on the shock-induced rocket separation from the mother plane (충격파에 의한 비정상 모선분리 현상 연구)

  • Kim Y. S.;Ji Y. M.;Lee J.-W.;Park J. S.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.10a
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    • pp.155-160
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    • 2004
  • This paper describes a supersonic separation of air-launching rocket from the mother plane. Three dimensional Euler equations were numerically solved to analyze steady/unsteady state fluid flows. To solve the Euler equations, named CFD-FASTRAN that is commercial computation code. The results of simulation clearly demonstrate effect of shock-expansion wave interaction between the rocket and the mother plane. Moreover, important influential factors at separating stage of the rocket were extracted with a comprehensive analysis. Finally, from the consideration of supersonic-separation, a guideline to safety-separation is given to the design of supersonic air-launching rocket.

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Analysis on Nonstationarity of Hydrologic Variable and Development of Bayesian Nonstationary Rainfall Frequency Analysis (국내 수문자료의 비정상성 특성 검토 및 Bayesian 비정상성 강수 빈도해석 기법 개발)

  • Kwon, Hyun-Han;Moon, Young-Il;Park, Rae-Gun;Park, Se-Hoon
    • Proceedings of the Korea Water Resources Association Conference
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    • 2009.05a
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    • pp.214-219
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    • 2009
  • 본 연구에서는 기후변동성 및 기후변화와 같은 외부충격을 극치수문사상 해석에 반영할 수 있는 비정상성 빈도해석 기법을 제안하고 서울지방 강수량에 대해서 검토를 실시하였다. 이러한 외부인자를 고려할 경우에 가장 큰 어려운 점은 극치분포의 매개변수를 효과적으로 추정하면서 동시에 불확실성을 정량화해야 한다는 점이다. 이러한 점에서 본 연구에서 제시한 Bayesian 방법은 상대적으로 우수한 해석 능력을 나타내고 있는 것으로 판단된다. 비정상성 빈도해석 기법을 서울지방 강수량에 선형경향성과 기후변화 영향을 고려하여 적용한 결과 현재에 비해 극치강수량에 발생 빈도가 크게 나타나는 특성을 보여주고 있다. 그러나 보다 신뢰성 있는 해석을 위해서 다양한 기상패턴 및 모형을 검토하는 것이 바람직 할 것으로 판단된다.

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Numerical Simulations of an Unsteady Shock Wave Propagating into a Helmholtz Resonator (Helmholtz 공명기 내부를 전파하는 비정상 충격파의 수치해석)

  • Lee, Y.K.;Gweon, Y.H.;Shin, H.D.;Kim, H.D.;AOKI, T.
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1643-1648
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    • 2004
  • When a shock wave propagates into a Helmholtz resonator, very complicated wave phenomena are formed both inside and outside the resonator tube. Shock wave reflection, shock focusing phenomena and shock-vortex interactions cause strong pressure fluctuations inside the resonator, consequently leading to powerful sound emission. In the present study, the wave phenomena inside and outside the Helmholtz resonator are, in detail, investigated with a help of CFD. The Mach number of the incident shock wave is varied below 2.0 and several types of resonators are tested to investigate the influence of resonator geometry on the wave phenomena. A TVD scheme is employed to solve the axisymmetric, compressible, Euler equations. The results obtained show that the configuration of the Helmholtz resonator significantly affects the peak pressure of shock wave focusing, its location, the amplitude of the discharged wave and resonance frequency.

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