• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.427-434
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• 1997

Heat transfer characteristics of a two-dimensional oblique impinging jet were experimentally investigated. The local heat transfer coefficients were measured by a thermochromic liquid crystal. The jet Reynolds number studied was varied from 10000 to 35000, the nozzle-to-plate distance(H/B) from 2 to 16, and the oblique angle($\alpha$) from $60^{\circ}$ to $90^{\circ}$. It was observed that the local Nusselt numbers in the minor flow region were larger than those in the major flow region at the same distance along the plate due to the higher levels in the turbulent intensity caused by more active mixing of the jet flow.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.7
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• pp.567-574
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• 2002

In the present study, ventilation flow rates and pressure rises through a road tunnel are simulated numerically using CFD with the various conditions such as roughness height, swirl angle of jet fan, entrance and exit effect and hub to tip ratio. By using a modified wall function, friction factor can be predicted under 10％ of error with respect to the Moody chart for the circular pipe flow and 15％, for the present tunnel. For more precise design, the effects of the swirl angle and hub to tip ratio of jet fan, which is not included in the theoretical equation of pressure rise by jet fan are necessary to be considered.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.109-112
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• 2002

The supersonic jet discharging from a petal nozzle is known to enhance mixing effect with the surrounding gas because it produces strong longitudinal vortices due to the velocity difference from both the major and minor axes of petal nozzle. In the present study, the supersonic free jet discharging from the petal nozzle is investigated experimentally. The nozzles used are 4, 6, and 8 lobed petal nozzles with a design Mach number of 1.7, and the flow fields are compared with a circular nozzle with the same design Mach number. The pitot impact pressures are measured using a fine pilot probe. The flow fields are visualized using a Schlieren optical method. The results show that the petal nozzle has more increased supersonic length compared with the circular jet.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2704-2707
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• 2008

We perform an active control on flow over a circular cylinder using a synthetic jet at Re=3900. The synthetic jet is issued from a cavity located inside the cylinder, generating a train of vortices near the surface. These vortices interact with and weaken the main vortices, resulting in drag reduction at a high frequency.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1447-1451
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• 2004

The laminar impinging jet thermal fields were investigated with or without magnetic fields. The transient phenomenon from steady to unsteady flow was founded at specific Reynolds number ranges. In unsteady flow region, the magnetic fields make flow stable. So the characteristics of heat transfer at impingement wall are changed

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.3
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• pp.394-401
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• 2002

The instantaneous flow characteristics of a round jet issuing normally into a crossflow has been studied using a flow visualization technique and particle image velocimetry. The effects of parameters such as jet inflow profile and turbulence intensity of the jet are evaluated for various Reynolds numbers in range between 735 and 3150, which are based on the crossflow velocity and jet-pipe diameter. The jet-to-crossflow velocity ratio is fixed at the value of 3.3. Instantaneous later tomographic images of the symmetry plane of the crossflow jet show that there exist very different natures in the flow structures of the near-field of the jet even though the velocity ratio is same. It is found that when the turbulence intensity of jet is elevated, the shear layer becomes much thicker due to the strong entrainment of the ambient fluid by turbulent interaction between the jet and crossflow. The detailed characteristics of instantaneous velocity and vorticity fields are presented to illustrate the effects of the above parameters on the vertical structures of the crossflow jet.

• Journal of Power System Engineering
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• v.5 no.3
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• pp.31-37
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• 2001

A study to obtain the enhancement of turbulence at low Reynolds number is carried out by adding ultrasonic force into the jet flow field of a coaxial circular pipe which can afford the sufficient data of flow characteristics with the shear flow and turbulence flow in spite of its simple shape. A coaxial circular flow field is made vertically in a large and transparent acryl tank. The time mean velocity vector, distribution, kinetic energy and turbulence intensity formed in the complex flow field of turbulence enhancement are investigated, observed and discussed at Reynolds number of 2,000, 3,000 and 5,000 by using PIV measurement, in results, the validity of ultrasonic to obtain the enhancement of turbulence is certified.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.2
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• pp.34-41
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• 2012

Thrust vector control system is a control device which is mounted on the exit of the nozzle to generate pitch, yaw and roll directional force by deflecting flow direction of the supersonic jet from the nozzle. Thermal and aerodynamic loads are acting on the surface of jet vane when it is exposed to the jet flow. Axial thrust loss and side thrust loss are affected by shock patterns and interactions between jet-vanes which varies with jet-vane geometry and turning angle. In this research, the performance estimation using the numerical simulation analysis of the nozzle is given and the investigation of the flow visualization and aerodynamic performance with the enforced power to the vane is taken.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.337-340
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• 2006

The present paper describes an experimental work to investigate a transonic resonance in supersonic jet that is discharged from a convergent-divergent nozzle. When the nozzle m: at low nozzle pressure ratios, the shock occurs within the divergent section of the nozzle. The transonic resonance of a jet flow is generated by an emission of strong acoustic tones due to the unsteadiness of the shock. A Schlieren optical system is used to visualize the supersonic jet flow In order to specify the flow resonance of a jet, acoustic measurements are performed to obtain noise spectra. The acoustic characteristics of transonic resonace are compared with those of screech tones. The results obtained show that unlike screech frequency, the transonic reso- nace frequency somewhat increases with increasing the nozzle pressure ratio.

• Journal of ILASS-Korea
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• v.1 no.4
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• pp.46-53
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• 1996

The present study is aiming at improving the performance of main nozzle of an air jet loom with a modified reed and auxiliary nozzles. The double coaxial pipe jets consisting of a central air jet and an annular air jet have been experimentally investigated. The duter jet has a potential core and a constant velocity. The inner jet through an inner long pipe is induced by the subatmospheric pressure near the inner nozzle edge, and the jet velocity of an inner pipe is always lower than that of a outer pipe. The static pressures of the main nozzle over a wide range of the nozzle tank pressure were measured, and the nozzle velocity and Mach numbers were analytically calculated. Experiment81 results indicate that the critical condition of Mach number of unity to occur at the two positions in a main nozzle; one of them is the needle tip and the other is the acceleration tube exit An increase in the tank pressure causes the critical throat condition to occur at the two positions above. The velocity of acceleration-tube exit is maximum at the critical length L* and flow patter in acceleration-tube over critical lengh remains unstable.