• 한국군사과학기술학회지
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• 제10권3호
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• pp.208-216
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• 2007

As the propellant mass is being accelerated out of the gun chamber along with the projectile, a continuous pressure gradient exists between the end of chamber and the base of the projectile. For this reason, the base pressure-travel curve is very important to design a conventional gun barrel in the interior ballistics, but it is not obtained briefly by empirical or theoretical method. In this paper, a simple relation between chamber pressure and base pressure was determined by the factor of base pressure(Cb) obtained from the experimental method. The simple relation gives a reasonable prediction for the reduction of pressure between the breech and the base of projectile owing to the axial gradient in the gun tube. The predictions have been validated by the infrared screen sensor and the PRODAS(PROjectile Design and Analysis System) for interior ballistic systems. Therefore, the base pressure-travel curve could be calculated from the chamber pressure measured by piezoelectric sensor. The base pressure-travel curve obtained from the simple relation offers initial information to gun barrel designer and is used for calculation of muzzle velocity.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.193-195
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• 2011

An abrupt increase of duct cross-section is frequently encountered in pressure reducing devices, valves of internal combustion engines and in gas pipelines. Supersonic flow in a rectangular duct passing an abrupt increase of cross-section is studied numerically. The behavior of base pressure of the dead-air region at sudden enlargement of the duct is clarified. This investigation concerns the determination of the base pressure, which is independent of the size of the enlarged part. Several flow patterns are identified with different enlargements according to the ratio between the downstream ambient pressure and the upstream reservoir pressure. Base pressure and the resulting shock-structure are highly depending on the size of duct enlargement. For a given duct, base pressure tends to minimum for a particular pressure ratio. In addition, the locations of secondary separation and reattachment points of the jet plume are found with respect to different duct enlargements.

• 한국추진공학회지
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• 제16권2호
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• pp.51-57
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• 2012

고속의 제트에서 기저압력은 유체역학 및 실용적 공학 적용의 관점으로 매우 중요한 분야중의 하나로 다루어져 왔다. 현재까지 비압축성 유동의 기저압력 특성들은 비교적 상세하게 알려져 있다. 하지만 천음속 혹은 초음속에서의 기저압력은 압축성 효과 및 충격파 발생으로 인해 매우 다르게 나타난다. 본 연구에서는 이러한 천음속 혹은 초음속에서의 기저압력특성에 관한 이해를 위해 선행된 실험 연구 결과를 바탕으로 수치해석적 연구를 수행하였다. 간단한 오리피스를 사용하여 기저 압력 조절하는 것에 주안점을 두었다. 기저 압력에 영향을 미치는 유동변수의 적용으로 여러 형태의 초음속 제트 플룸을 분석하였다. 선행된 실험결과를 모사하여 수치해석 기법의 타당성을 조사하였으며, 계산된 기저압력과 오리피스의 유출계수에 관하여 논의하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.318-320
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• 2011

Numerical study was conducted to simulate the heat transfer on the real launch vehicle base. Three different base temperatures were chosen, to simulate the heat accumulation on the base. Moreover, six different pressure ratio conditions were used to express the different air conditions. As a result, the table that can used to estimate the base heat fox along the base temperature and pressure condition was made.

• 한국진공학회지
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• 제20권2호
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• pp.141-145
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• 2011

ZnO:Al 박막을 RF magnetron sputtering 법을 이용하여 초기 압력에 따라 증착하고 박막의 구조적, 광학적, 전기적 특성을 연구하였다. 초기 압력 변화에 의해 ZnO:Al 박막의 특성의 변화를 확인하였고 고품질의 박막을 얻을 수 있었다. 모든 ZnO:Al 박막에서 (002)면의 우선 배향성을 보였으며 가시광선 영역(400~800 nm)에서 85% 이상의 좋은 투과도를 보였다. 초기 압력이 낮아질수록 결정성, 비저항 그리고 성능지수 특성이 향상됨을 확인하였다. 초기 압력에 따른 비저항의 향상은 결정립 크기 변화에 의한 것으로 판단된다.

• 한국항공우주학회지
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• 제48권11호
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• pp.849-859
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• 2020

반경험식과 상용 전산해석도구를 이용하여 비행 속도 및 챔버 압력에 따른 유도무기의 기저항력을 예측하였으며, 두 해석 결과는 대체적으로 일치함을 보였다. 노즐에 의한 분사 제트의 과대/과소 팽창에 따라 기저부의 유동 특성과 기저항력의 차이가 관찰되었다. 과대팽창 조건에서는 기저부 상단에 팽창파가 발생되면서 기저부의 압력이 감소하였으며, 외부 자유류의 마하수가 증가함에 따라 팽창파의 강도가 강해지면서 기저부 압력 더욱 감소하였다. 과소 팽창 조건에서는 노즐 후류의 영향으로 기저부 주위에 충격파가 발생하고 이로 인해 기저부 압력이 증가하였으며, 챔버의 압력이 증가할수록 그 영향이 크게 나타났다. 동일 챔버 압력 조건에서는 자유류 마하수가 증가함에 따라 기저부에서 생성되는 충격파가 하류로 이동하면서 기저 압력이 감소하는 특성이 관찰되었다.

• Wind and Structures
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• 제12권1호
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• pp.49-61
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• 2009

A method is presented to estimate the form drag and the base pressure on a triangular cylinder in the presence of blockage effect. The Strouhal number, which is found to increase with the flow constriction experimentally by Ramamurthy & Ng (1973), may be decoupled from the blockage effect when re-defined by using the velocity at flow separation and a theoretical wake width. By incorporating this wake width into the momentum equation by Maskell (1963) for the confined flow, a relationship between the form drag and the base pressure is derived. Independently, the experimental data of surface pressure from Ramamurthy & Lee (1973) are found to be independent of the blockage effect when expressed in terms of a modified pressure coefficient involving the pressure at separation. Using the potential flow model by Parkinson & Jandali (1970) and its subsequent development in Yeung & Parkinson (2000) for the unconfined flow, a linear relation between the pressure at separation and the form drag is formulated. By solving the two equations simultaneously with a specified blockage ratio and an apex angle of the triangular cylinder, the predictions of the drag and the base pressure are in reasonable agreement with experimental data. A new theoretical relationship for the Strouhal number, pressure drag coefficient and base pressure proposed in this study allows the confinement effect to be appropriately taken into consideration. The present approach may be extended to three-dimensional bluff bodies.

• Geomechanics and Engineering
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• 제17권5호
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• pp.413-420
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• 2019

The changes in earth pressure and ground settlement due to underground excavation near an existing retaining wall were studied experimentally according to the separation distance between the underground excavation and the retaining wall. In addition, this study attempted to experimentally prove that the arching phenomenon occurred during the construction of the underground space. A model tank having 120 cm in length, 160 cm in height, and 40 cm in width was manufactured to simulate underground excavation through the use of five separated base wall bodies. The variation of earth pressure on the retaining wall was measured according to the underground excavation phase through the use of 10 separated right wall bodies. The results showed that the earth pressure on the retaining wall was changed by the lowering of the first base bottom wall; however, the earth pressure was not changed significantly by the lowering of the third base bottom wall, since the third base wall had sufficient separation distance from the retaining wall. Lowering of the first base wall induced a decrease in the earth pressure in the lower part of the retaining wall; in contrast, lowering of the first base wall induced an increase in the earth pressure in the middle part of the retaining wall, proving the arching effect experimentally. It is necessary to consider the changes in earth pressure on the retaining wall in designing earth retaining structures for sections where the arching effect occurs.

• 한국전산유체공학회지
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• 제20권2호
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• pp.16-22
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• 2015

The pressure is generally lower than that of the freestream at the base of a missile body due to the energy loss by the flow separation around the edge of the base. The base pressure changes in the presence of the thrust jet due to the interaction between the base flow of the missile and the jet flow. In this study, behavior of the missile base pressure by the change of the jet exit pressure and the freestream condition is investigated using the CFD(Computational Fluid Dynamics) method. Effects of the grid type and the freestream condition are tested. The results are compared with the semi-empirical predictions and the flight test data. The CFD results agree well with the flight test data. The semi-empirical predictions overestimate the base pressure when jet thrust is strong for low freestream speed.

• 한국전산유체공학회지
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• 제2권2호
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• pp.9-17
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• 1997

The performance of several turbulence models in computing an axisymmetric supersonic base flow is investigated. A compressible Navier-Stokes code, which incorporates k-ε, k-ω model and Reynolds stress closure with three kinds of pressure-strain correlation model, has been developed using implicit LU-SGS algorithm with second-order upwind TVD scheme. Numerical computations have been carried out for Herrin and Dutton's base flow. It is observed that the two-equation models give large backward axial velocity approaching to the base and somewhat larger variation of base pressure distribution than the Reynolds stress model. It is also found that the Reynolds stress model with third order pressure-strain model in the anisotropy tensor predicts most accurate mean flow field.