• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.4
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• pp.59-67
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• 2016

Numerical simulations have been performed to investigate thrust characteristics of a through-type pintle nozzle with or without flow separation at various operating altitudes. The low Reynolds number $k-{\varepsilon}$ with compressibility correction proposed by Sarkar are applied. The detail flow structures are observed and static pressures along nozzle wall are compared with experimental results. The flow separation in the pintle nozzle disappears and jet plume strongly expands as its operating altitude increases. To evaluate the thrust characteristics, the momentum term and pressure term of thrust are analyzed. Thrust and thrust coefficient at altitude 20 km are about 10% more than them at the ground 0km.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.321-327
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• 2008

Performance characteristics of the axi-symmetric supersonic exhaust diffuser (SED) with a second throat are numerically investigated. Computational strategy repeats those for a straight exhaust diffuser with zero-secondary flows. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with standard wall function are solved to simulate the diffusing evolutions of the nozzle plume. The methodology is validated with accuracy. To predict the improvement of starting performance by second throat diffuser, diffuser characteristic curve due to the SED equipped with the second throat is speculated with respect to that of a straight area type as a function of nozzle stagnation pressure. Principal physics caused by the of the second throst is also addressed in terms of a second throat area ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.299-304
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• 2008

Starting characteristics of the axi-symmetric second throat exhaust diffuser (STED) with zero-secondary flows are numerically investigated. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with enhanced wall treatment are solved to simulate the diffusing evolutions of the nozzle plume. Minimum (optimum) starting pressure difference of 20$\sim$25% between 1-D theory and the measured data validated from previous results[5] is also applied to predict the range of an effective diffuser expansion ratio (Ad/At) in this system.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.11
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• pp.78-83
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• 2010

Since a tower crane is too high for a worker to ascend and by the wind in the high altitude, the possibility of a safety accident is very high, a lift assist is used. In this study, the hydraulic fall prevention device using the pressure generation device by Seok, et al. was developed. For this, the effects on the fall prevention performances of factors such as gear clearance, oil viscosity, rotative velocity and so on were evaluated by the analysis of fluid flow using FEM and the prototype was producted and a function test was performed.

• Journal of Aerospace System Engineering
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• v.7 no.3
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• pp.33-38
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• 2013

The air data measured from the static pressure, the dynamic pressure and etc. of an airplane is used for calculation of many flight parameters(altitude and airspeed and so on) and these values applied to flight safety and navigation flight. The pitot-static system of the development airplane is calibrated by finding of pitot-static system's error using tower fly-by, trailing cone method and etc. This paper is describing for the introduction of the trailing cone method and major items for test planning, preparation, operation and results for air data calibration flight test performed, considering efficiency and safety during KC-100 development project.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.487-491
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• 2009

A study is analyzed on the design factor of Center-body diffuser and performed on conceptual design of Center-body diffuser with Computational Fluid Dynamic. The flow field of Center-body diffuser is calculated using Axisymmetric two-dimensional Navier-Stokes equation with $k-{\omega}$ turbulence model. The center-body diffuser is compared with second throat exhaust diffuser in terms of starting pressure, the degree of vacuum pressure, the design factor.

• Atmosphere
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• v.20 no.3
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• pp.355-366
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• 2010

The tropopause pressure in the Arctic region is calculated by the conventional thermal and dynamical methods using 30-year reanalysis data. The tropopause pressures determined thermally and dynamically both show semiannual cycles with one peak in April and May, and another in October, contrary to the tropopause temperatures. Although tropopause levels are higher both in January and July, the level of the tropopause in January seems to be associated with the stratospheric temperatures while that of July seems to be associated with the tropospheric temperatures. During the 30-year period the most significant trend appears in April, and it is shown that the altitude of the Arctic tropopause has been rising. Although a potential reason for this trend is stratospheric cooling due to ozone depletion, significant tropospheric warming in April is considered to be another reason.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.392-399
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• 2008

Accurate measurement of speed and altitude of flying vehicles in air data system remains a critical technical issue. A highly reliable Pitot-static probe is required to obtain air data such as total pressure and static pressure. In this study, an analysis of the characteristics of flowfield around the Pitot-static probe was performed by using a Navier-Stokes CFD code. In addition, for the purpose of finding an optimal configuration, a technique based on the response surface method is applied to the problem with design parameters including shape of the nose section and cone angle. It is shown that the optimal configuration fulfills the MIL specification in wider range of high angles of attack.

• Journal of Aerospace System Engineering
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• v.14 no.4
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• pp.1-9
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• 2020

The characteristics of an aerospike pintle nozzle system with excellent altitude compensation were analyzed using cold air testing. It was confirmed that reducing the stroke of the aerospike nozzle is effective in increasing the thrust. However, the results of additional numerical analysis indicated that the discharge coefficient factor was significantly lower at the maximum stroke. The Vena contracta due to the cowl reduction angle decreased the effective nozzle throat area at the maximum stroke and hindered expansion. Complementing the cowl design may thus increase the efficiency of a solid-propellant rocket engine that uses the aerospike pintle nozzle system.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.145-148
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• 2006

In order to design a micro-thruster which controls the altitude of a space vehicle for a very long lifetime, the flow field should be analyzed considering the nozzle geometry and the difference between stagnation and environmental pressures and so on. This paper describes the axisymmetric non-reacted computational results which were carried out to understand the basic flow phenomena according to the high nozzle pressure ratio. The area ratio is about 56 and the diameter of a nozzle exit is about 0.46 inch. The Mach cell and waves are predicted well.