• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.749-752
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• 2004

In a liquid-fueled ramjet engine, the insufficient mixing and evaporation result in the low combustion efficiency and combustion instability. Improving its spray characteristics and devising a means of mixing fuel droplets with air may compensate these disadvantages of liquid fuel ramjet engine. The jet penetrations of various fuel injectors were measured to investigate the spray characteristics of a liquid-fueled ramjet engine under high pressure air-stream conditions. The penetrations in high pressure conditions are smaller than the values calculated from Inamura's or Lee's equations, and, in the high pressure conditions, the jet penetrations are similar each other. In the dual hole injectors, the jet penetrations of rear orifice is rapidly increased due to the reduction of the drag, which is created by the jet column of front orifice. The jet penetration of rear orifice is increased because of the drag reduction created by the jet column of the front orifice. And, because of the drag reduction formed by the column of jet, the jet penetration in the rear orifice of dual hole injector is much larger than the jet penetration of single hole injector. As the distances of the orifice are increased, the jet penetrations of the rear orifice decrease.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.164-165
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• 2003

The problem of a bluff body oscillating in a fluid flow has been receiving a great deal of attention. When a bluff body is placed in a flow, it experiences fluctuating hydraulic forces in both transverse and stream-wise directions. It is caused by the formation of vortices behind the body, which could cause large damages of structures. It is called the flow-induced vibrations. In this article, it is investigated the effects of that side-jets and rear-jet, which is applied to control the vortex shedding. The rear-jet is available to control the flow-induced vibrations according as the body shapes and the velocity of fluid flow in which the galloping phenomena is not appeared.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.759-764
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• 2000

In this study, the confined laminar flow around a square cylinder, which ejects a either on the front face or on the rear face, is numerically simulated. In each case, three ratios of jet velocity to the fixed upstream velocity are considered. In all cases of the rear fuel jet, the high mass-fraction region is formed along the streamlines from the jet exit. In case of front jet, drag is significantly decreased when the jet velocity ratio is greater than 1. The results obtained exhibit flow and scalar-mixing characteristics encountered in a planar combustor

• Journal of ILASS-Korea
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• v.9 no.2
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• pp.34-40
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• 2004

In a liquid-fueled ramjet engine, the insufficient mixing and evaporation result in the low combustion efficiency and combustion instability. Improving its characteristics and devising a means of fuel droplets with air may compensate these disadvantages of liquid fuel ramjet engine. The jet penetrations of various fuel injectors were measured to investigate the spray characteristics of a liquid-fueled ramjet engine under high pressure air-stream conditions. The penetrations in high pressure conditions are smaller than the values calculated from Inamura's or Lee's equations, and the jet penetrations in the high pressure conditions have a similar tendency. In the dual orifice injectors, the jet penetrations of rare orifice is rapidly increased due to the reduction of the drag, which is created by the jet column of front orifice. The jet penetration of rare orifice is increased because of the drag reduction created by the jet column of the front orifice. Because of the drag reduction formed by the column of jet, the jet penetration in the rear orifice of dual orifice injector is much larger than the jet penetrations of single orifice injector. As the distances of the orifice are increased, the jet penetrations of the rear orifice decrease.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1644-1651
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• 2000

In this study, the confined laminar flow and transport around a square cylinder with a planar fuel jet are numerically simulated. Both rear and front jets are considered, respectively. In each case, various ratios of the jet velocity to the fixed upstream velocity are taken into consideration. In case of the rear jet, the high mass-fraction region is formed along the streamlines from the jet exit, and the oscillation of the force on the square cylinder eventually disappears as the jet velocity is close to the upstream velocity. In case of the front jet, drag is significantly reduced when the jet velocity ratio is grater than 1. The results obtained exhibit flow and scalar-mixing charactered in a planar combustor.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.1
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• pp.69-75
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• 2004

This paper presents the thermal characteristics analysis of a high-speed motor-separated spindle system consisted of angular contact ball bearings and built-in motor with oil-jet lubrication. The spindle system is composed of the main spindle and sub-spindle which are mechanically connected by a flexible coupling. The spindles are supported by two front and rear bearings, and the built-in motor is located between the front and rear bearings of the sub-spindle. The thermal analysis model of spindle system is constructed by the finite element method, and the thermal characteristics in the design stage are estimated based on temperature distribution and heat flow under the various testing conditions related to material of bearing ball, spindle speed and coolant temperature.

• Fire Science and Engineering
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• v.18 no.4
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• pp.27-34
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• 2004

We have conducted a numerical simulation under three-dimensional unsteady conditions in order to analyze the effect of flow and CO₂ mass transfer according to the distance between the CO₂ nozzle of CO₂ fire fighting system and the rear wall in a protection space. Flow fields and CO₂ concentration fields were measured. The different recirculation flow form and wall jet was developed according to increasing the distance between CO₂ nozzles and rear wall. In all the case, CO₂ mass transfer was generated toward the center of a protection space from each walls, but the CO₂ mass fraction of front and rear areas based on CO₂ nozzles showed higher or lower by increasing the distance between CO₂ nozzle and rear wall.

• Journal of computational fluids engineering
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• v.17 no.2
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• pp.85-92
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• 2012

Flows over a square cylinder with and without plasma actuation are numerically investigated to see whether plasma actuation can effectively modify vortex shedding from the cylinder and reduce the drag and lift fluctuations. In this study, a plasma synthetic jet actuator is mounted on the rear side of cylinder as a means of direct-wake control. The effect of plasma actuation is considered by adding a momentum forcing term in the Navier-Stokes equations. Results show that the reduction of mean drag and lift fluctuations is obtained for both steady and unsteady actuation. However, the steady actuation is better than the unsteady one in terms of mean drag as well as drag fluctuations. With the strong steady actuation considered, the interaction of two separating shear layers from rear corners is effectively weakened due to the interference of synthetic jets. It results in a merging of synthetic-jet and shear-layer vortices and the increase of vortex shedding frequency. On the other hand, the unsteady actuation generates pulsating synthetic jets in the near wake, but it does not change the vortex shedding frequency for the actuation frequencies considered in this study.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.30 no.1
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• pp.12-19
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• 2022

The exhaust wake of an aircraft engine is discharged in a high temperature and high speed, which can damage objects such as an aircraft in the rear. The exhaust wake can lift small foreign substances lying on the ground or falling off, and the floating foreign substances can enter the intake duct of the aircraft moving from the rear and cause engine FOD (Foreign Object Damage). This study experimentally analyzed how the engine exhaust wake generated from military jet fighters affects the movement of foreign substances and evaluated the effects of foreign substances on the damaged area by measuring wake velocity. The simulation and field experimental results confirmed that the effect of exhaust wake increases as the rear position closer, and that foreign substances lifted by the wake can act as FOD to the adjacent rear aircraft.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.317-321
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• 2007

PSP (Pressure Sensitive Paint) technique can measure continuous pressure field by analyzing the oxygen quantity using optical method. The surface pressure of down stream after the sonic jet that injected transversely into the supersonic freestream was measured by PSP technique. Moreover the effect of various rectangular shaped cavities in front of the jet was measured by PSP technique. A comparison of the PSP results with conventional pressure tap and CFD indicates good agreement. The result shows that the cavity affects the pressure distribution in the rear of the jet injection.