• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.21-31
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• 2017

In the present study, theoretical and numerical analyses have been carried out to investigate the detailed flow characteristics during the mode transition. The theoretical analysis rearranged the knowledge of gasdynamics and the previous studies, and the numerical analysis has conducted to solve the 2D unsteady compressible Navier-Stokes equations with a fully implicit finite volume scheme. To validate the numerical analysis, the experiment was compared with it. The total temperature at the inlet of isolator and the hydrogen fuel equivalent ratio were changed to investigate their effects on the mode transition phenomenon. As the results, the numerical analysis reproduced well the experiment qualitatively, the increment in the hydrogen fuel equivalent ratio induced the scram-mode to ram-mode transition which is discontinuous with a non-allowable region, and the variation in the total temperature changed the boundary of the mode transition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.86-89
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• 2005

A computational work has been performed to investigate the aerodynamics of a projectile which is launched from the two-stage light gas gun. A moving coordinate method for a multi-domain technique is employed to simulate unsteady projectile flows with a moving boundary. The effect of a virtual mass is added to the axisymmetric unsteady Euler equation system. The computed results reasonably capture the major flow characteristics which we generated in launching the projectile supersonically, such as the interaction between the shock wave and the blast wave, the interaction between the vortical flow and the barrel shock, and the steady under-expanded jet. The present computational results properly predict the velocity, acceleration, and drag histories of the projectile.

• Journal of KSNVE
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• v.11 no.2
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• pp.285-291
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• 2001

The impingement of a weak shock wane discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was varied in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.113-122
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• 2000

Dynamic structures of unsteady $CH_4$/Air jet diffusion flames with flame-vortex interaction were numerically investigated. A time-dependent, axisymmetric computational model was adopted for this calculation. Two step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including gravitational effect show that the large outer vortices and the small inner vortex street can be well simulated without any additional disturbances in the downstream of nozzle tip. It was found that the temperature and species concentrations had various values for the same mixture fraction in flame-vortex interaction region. This unsteady jet flame configuration accompanying flame-vortex interaction is expected to give good implications for the structure of turbulent flames.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.562-567
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• 2000

The Impingement of a weak shock wave discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was vaned in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.23-28
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• 2002

TNumerical simulations of the supersonic impinging jet flows are carried out using the 3D Navier-Stokes code. This paper is focuses on the unsteady flow features associated with stagnation bubbles and other oscillatory behavior. The 3D code was validated by reproducing the results of Lamont's experiments. Computation is carried out for the cases in which the unsteadiness of the plate shock has been observed experimentally. The computational results confirm the oscillatory feature in several kHz. Unsteady calculation with algebraic turbulence model is also performed. It is found that the laminar and turbulent results have some discrepancy in the transient period. However, both of them reveal the oscillatory behavior with similar frequency.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.126-131
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• 2003

A series of computational simulations have been carried out for supersonic flows in a scram jet engine with and without a cavity. Transverse injection of hydrogen, a simplest form of fuel supply, is considered in the present study with the injection pressure varying from 0.5 to 1.5 MPa. The corresponding equivalence ratios are 0.167 - 0.50. The work features detailed resolution of the flow dynamics in the combustor, which was not typically available in most of the Previous studies. In particular, oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is related not only to the cavity, but also to the intrinsic unsteadiness in the flowfield. The interactions between shock waves and shear layer may cause a large excursion of flow oscillation. The role of the cavity and injection pressure are examined systematically.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.74-92
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• 2000

A numerical analysis has been conducted to study the transient flowfield during the transition from the booster to sustainer phase in an integrated rocket ramjet (IRR) propulsion system. Emphasis is placed on the unsteady inlet aerodynamics, fuel/air mixing in an entire ramjet engine during the flow transient phase. The computational geometry consists of the entire IRR engine, including the inlet, the combustion chamber, and the exhaust nozzle. Turbulence closure is achieved using a low-Reynolds-number two-equation model. The governing equations are solved numerically by means of a finite-volume, preconditioned flux-differencing scheme over a wide range of Mach umber. Various important physical processes are investigated systemically, including terminal shock train.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.499-507
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• 1988

The pressure suppression pool of BWR(Boiling Water Reactor) is subjected to hydrodynamic impact in the event of a LOCA(Loss of Coolant Accident). The pressure increase in the reactor dry cell would force the existing water of a vent pipe into the suppression pool. When the water is ejected through the pipe opening into the suppression pool, an abrupt downward force is transmitted to the suppression pool floor. Consequently, many structures installed within the pool must be able to withstand these forces. In order to determine the optimum safe locations of the pool structures, numerical analysis have been carried out to investigate the hydrodynamic behavior of the water jet. In the present analysis, a two-dimensional numerical model is utilized to solve transient flow equations.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.19-28
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• 2017

Effects of cavitation and hydraulic flip in circular and elliptical nozzles on the flow characteristics have been studied. Spray tests were conducted using injectors with different ratios of an orifice length(L) to a diameter(d) and of a major axis diameter(a) to a minor axis diameter(b). With the increment of an injection pressure drop, discharge coefficients slightly decreased in cavitation flows, and those suddenly dropped and were almost constant in hydraulic flip flows. For elliptical nozzles with L/b > 8 and L/a < 8, discharge coefficients and flow patterns showed different results from those in previous circular nozzles. When a flow in the elliptical nozzle was under steady condition, as the liquid column went downstream from the nozzle, its spray angle a little decreased in the plane of a major axis and increased in the plane of a minor axis.