• Proceedings of the KSME Conference
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• 2002.08a
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• pp.127-130
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• 2002

Supersonic jet flow has been applied to many various industrial applications of manufacturing fields. Such a supersonic jet is generally classified by three flow patterns, depending on the flow state at nozzle exit, that is, under-, correctly- and over-expanded flows. Of these three flows, the correctly-expanded supersonic jet is most frequently used since it provides a maximum performance of a flow device. However detailed information on what conditions are the Jet correctly expanded at the exit of nozzle is not well known. In the current study, computations are applied to the axisymmetric, compressible, Navier-Stokes equations. The design Mach number used are 2.0,1.2 and 2.6. The computational results obtained are compared with the previous experimental ones. A theoretical analysis is conducted to predict the major features of the correctly-expanded jet. The results show that the jet core length is increased as Mach number is increased.

• Advances in aircraft and spacecraft science
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• v.1 no.4
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• pp.443-454
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• 2014

An experimental study was conducted to investigate the effect of Reynolds number on compressible convex-corner flows, which correspond to an upper surface of a deflected flap of an aircraft wing. The flow is naturally developed along a flat plate with two different lengths, resulting in different incoming boundary layer thicknesses or Reynolds numbers. It is found that boundary layer Reynolds number, ranging from $8.04{\times}10^4$ to $1.63{\times}10^5$, has a minor influence on flow expansion and compression near the corner apex in the transonic flow regime, but not for the subsonic expansion flow. For shock-induced separated flow, higher peak pressure fluctuations are observed at smaller Reynolds number, corresponding to the excursion phenomena and the shorter region of shock-induced boundary layer separation. An explicit correlation of separation length with deflection angle is also presented.

• Journal of the Semiconductor & Display Technology
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• v.7 no.2
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• pp.55-58
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• 2008

The objective of the research is to design, manufacture and test a Mass Flow Controller(MFC) capable of measuring compressible fluid flows based on a "bucket and stop-watch"method. The basic principle is the measurement of time, where the time taken to fill and empty a bucket of known volume is measured. This method of flow measurement is a new concept when compared to a commercilized current mass flow controller. For the flow meter to be able to compete with established designs it not only must be comparable in cost and robustness, it must be very accurate and reliable as well. This device should be able to handle fluid flows in the range of 0.1ml/min to 10ml/min within an accuracy of ${\pm}$1%. A possible application for a device such as this is in electronics industry where arsenic gas is used in the production of silicon chips.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.187-195
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• 2012

This paper deals with numerical computations of cryogenic flows around turbopump inducer. Firstly, we introduce numerical methods to compute compressible/incompressible cryogenic two-phase flow. As a validation problem, computation results of 2 dimensional/axi-symmetric cryogenic flow will be presented. In this process, various cavitation model will be compared. Finally, numerical simulation of 3 dimensional turbopump inducer will be presented.

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.29-34
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• 1998

An efficient 3-dimensional compressible solver is developed using the second-order upwind TVD scheme and the multigrid diagonalized ADI method. The multigrid method is improved so that the present DADI algorithm obtains better convergence rates. Results are computed on Cray C90 computer for transonic unsaperated flows past ONERA-M6 wing to demonstrate the accuracy and efficiency. The results show good agreement with experimetal data. A reduction of four orders of residual for 3-dimensional transonic flow is obtained about 99 seconds.

• 한국전산유체공학회:학술대회논문집
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• 2008.08a
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• pp.75.3-75.3
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• 2008

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.337-345
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• 2002

The present study addresses a computational result of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Wavier-Stokes equations are solved using a finite volume method that makes use of the second order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral scheme for time derivatives. The steady solutions of the governing equation system are validated with the previous experimental data to ensure that the present computational method is valid to predict the critical nozzle flows. In order to simulate the effects of back pressure fluctuations on the critical nozzle flows, an excited pressure oscillation with an amplitude and frequency is assumed downstream of the exit of the critical nozzle. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thus giving rise to the applicable fluctuations in mass flow rate through the critical nozzle, while for high Reynolds numbers, the pressure signals occurring at the exit of the critical nozzle do not propagate upstream beyond the nozzle throat. For very low Reynolds number, it is found that the sonic line near the throat of the critical nozzle remarkably fluctuateswith time, providing an important mechanism for pressure signals to propagate upstream of the nozzle throat, even in choked flow conditions. The present study is the first investigation to clarify the unsteady effects on the critical nozzle flows.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.459-464
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• 2000

In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the Pressure drop, computations using the mass-averaged implicit Wavier-Stokes equations were applied to the axisymmetric pipe flows with the operating pressure ratio from 1.5 to 20.0. The standard k-e turbulence model was employed to close the governing equations. Numerical calculations were carried out for some combinations of the multiple orifice configurations. The present CFD data showed that the orifice systems, which have been applied to incompressible flow regime to date, can not be used for the hint operating Pressure ratio flows. The orifice interval did not strongly affect the total pressure drop but the orifice area ratio more than 2.5 led to high pressure drops. The total pressure drop rapidly increased in the range of the operating pressure ratio from 1.5 to 4.0, but it did not depend on the operating pressure ratio over 4.0.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.8-17
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• 2005

It is well known that preconditioning methods are efficient for convergence acceleration in the compressible low Mach number flows. In this study, the original Euler equations and three differently nondimensionalized preconditioning methods are implemented in two dimensional inviscid bump flows using the 3rd order MUSCL and DADI schemes as numerical flux discretization and time integration, respectively. The multigrid and local time stepping methods are also used to accelerate the convergence. The test case indicates that a properly modified local preconditioning technique involving concepts of a global preconditioning allows Mach number independent convergence. Besides, an asymptotic analysis for properties of preconditioning methods is added.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.92-98
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• 2005

Screen can provide any disturbed resistance that affects the change in characteristics of turbulence, velocity and pressure distributions of the flow field, and thus it has been widely used to control the flow. Some previous related studies for compressible flows have limitations such as, considering relatively low-Mach-number flows in the range of 0.3 ∼ 0.7, and not observing the detailed shock structures of the flow fields. An experimental study on highly compressible axi-symmetric supersonic jet flow fields behind wire-gauze screen has thus been carried out. Continuous/instantaneous flow images by Schlieren flow- visualization technique and the information of Pitot pressure/flow-noise measurements of the flow field behind the screen for various jet expansion conditions have been obtained. Effects of various porosity and inclination angles of the screen at the nozzle exit have also been investigated, and the experimental results have been compared to the case with no screen installed.