• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.94-97
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• 2003

램젯 공기 흡입구에 연소실의 압력파 섭동이 미치는 영향에 대해 살펴보았다. 연소실의 압력파 섭동은 500Hz의 주파수를 가지며, 출구 배압의 20%의 진폭으로 가정하였다. 계산결과는 흡입구 내에서 섭동압력에 의한 수직충격파의 거동의 특성을 보여주었으며, 섭동압력과 목부분의 수직 충격파는 약180도의 위상차를 가지고 있었다. 이러한 해석 결과로부터 하류 섭동파와 흡입구 유입 유량의 상관관계를 살펴보았다. 충격파가 카울 앞으로 이동된 상태에서는 아임계상태가 되며, 설계유량보다 작아졌고, 매 주기 하류 섭동이 시작되는 시점에서 급격한 유량 감소를 볼 수 있었다.

• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.286-294
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• 2006

Flows in a ramjet inlet is simulated for the study of the rocket-ramjet transition. The flow is unsteady, two-dimensional axisymmetric, compressible and turbulent. Double time marching method is used for the unsteady calculation and HLLC method is used as a higher order MUSCL method. As for turbulent calculation, $\kappa-\omega$ SST model is used for more accurate viscous calculations. Sinusoidal pressure perturbation is given at the exit and the flow fields at the inlet is studied. The cruise condition as well as the ground test condition are considered. The pressure level for the ground test condition is relatively low and the effect of the pressure perturbation at the combustion chamber is small. The normal shock at the cruise condition is very sensitive to the pressure perturbation and can be easily detached from the cowl when the exit pressure is relatively high. The sudden decrease in the mass flux is observed when the inlet flow becomes subcritical, which can make the inlet incapable. The amplitude of travelling pressure waves becomes larger as the downstream pressure increases, and the wavelength becomes shorter as Mach number increases. The phase difference of the travelling perturbed pressure wave in space is 180 degree.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.152-160
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• 2004

Studies to investigate the influence on hydraulic acoustic wave were conducted using pressure swirl atomizer under making frequency range from 0 to 60Hz using water as a propellant. Pressure oscillation from hydraulic sources gives a strong influences on atomization and mixing processes. The ability to drive these low frequency pressure oscillations makes spray characteristics changeable. The effect of pressure perturbation and its spray characteristics showed that low injector pressure with pressure pulsation gives more significantly than high injector pressure with pressure perturbation in SMD, spray cone angle, breakup length. Moreover, this data could be used for prediction of low combustion instability getting G factor.

• 천문학회지
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• 제12권1호
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• pp.1-5
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• 1979

The usual assumption of the pressure equilibrium between the convective elements and the surrounding fluid has been dropped, and the effects of the pressure perturbation of the convective element on its velocity and T perturbation have been estimated.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.111-118
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• 1999

In this paper, linearized dynamic characteristics of parallel line pivoted pad thrust bearing(hereinafter refer to PLP thrust bearing) was analyzed by perturbation method with inlet pressure. Inlet pressure and excitation frequency irfluence dynamic characteristics of PLP thrust bearing at all operating condition, such as angular pivot position, mass of pad. Therefore, the characteristics is have to analyzed with inlet pressure, excitation frequency, mass of pad and thickness of pad. Otherwise, the analysis is able to estimate the characteristics over or under.

• Tribology and Lubricants
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• 제16권4호
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• pp.274-281
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• 2000

In this paper, linearized dynamic characteristics of parallel line pivoted pad thrust bearing (here-inafter refer to PLP thrust bearing) was analyzed by perturbation method with inlet pressure. Inlet pressure and excitation frequency influence dynamic characteristics of PLP thrust bearing at all operating conditions, such as angular pivot position, mass of pad. Therefore, the characteristics have to be analyzed with inlet pressure, excitation frequency, mass of pad and thickness of pad. Otherwise, the analysis may be over or under estimate.

• 한국추진공학회지
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• 제2권3호
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• pp.36-46
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• 1998

초음속 유동에서 발생하는 충격파는 일반적으로 충격파 상류와 하류의 압력비에 의해 일반적으로 결정된다. 본 연구에서는 충격파의 진동현상을 규명하기 위한 연구의 일환으로, 미소교란법(small perturbation method)을 이용하여 이론해석을 수행하였으며, 충격파 하류의 유동장에 에너지 손실을 적용하여 충격파의 안정성을 이론적으로 해석하였다. 이론해석에서는 충격파 상류에 경계층 유동에서 발생하는 난류변동이나 주류에서의 압력변동이 충격파의 진동과 관련된다고 생각하여, 충격파 상류의 유동에 미소압력변동을 적용하여 충격파의 진동특성을 해석하였다. 본 연구의 결과들을 타 연구의 결과와 비교하였으며, 열선풍속계(hot wire)를 이용한 실험적 연구결과와 비교하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.601-606
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• 2004

Vibration spectrums of the test loop according to flow conditions were analyzed in order to identify the sources of vibration at peak frequencies. While a flow condition of the sweep test was changed by varying pump rotational speed from 450 rpm to 1500 rpm by the step 150 rpm, midspan acceleration of the test section in width-direction and dynamic pressure perturbation in the test section were measured. Other sources of vibration due to the flow structure interactions, such as acoustic resonance, blade pulsing frequency and bellows wrinkles, were investigated. Pressure perturbation in the section and acoustic resonance due to branch pipe give major effects to the vibration of the test section in high frequency range of 1.5 kHz to 2.8 kHz.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1286-1291
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• 2004

In order for studying pressure-coupled dynamic responses of droplet vaporization, open-loop experiment of an isolated droplet vaporization exposed to pressure perturbations in stagnant gaseous environment is numerically conducted. Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous nitrogen. Results show that wave instability in view of pressure-coupled vaporization response seems more susceptible at higher pressures and higher wave frequencies. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Augmentation of perturbation frequency also enhances amplification due to the reduction of phase differences between pressure perturbation and surface temperature fluctuation.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.155-164
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• 2004

In order for studying pressure-coupled dynamic responses of droplet vaporization, open-loop experiment of an isolated droplet vaporization exposed to pressure perturbations in stagnant gaseous environment is numerically conducted, Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous nitrogen. Results show that wave instability in view of pressure-coupled vaporization response seems more susceptible at higher pressures and higher wave frequencies. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Augmentation of perturbation frequency also enhances amplification due to the reduction of phase differences between pressure perturbation and surface temperature fluctuation.