• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.329-334
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• 2007

An axisymmetric supersonic jet screech in the Mach number range from 1.07 to 1.2 is numerically simulated. The axisymmetric mode is the dominant screech mode for an axisymmetric jet. The Reynolds-averaged Navier-Stokes equations in the conjunction with modified Spalart-Allmaras turbulence model are employed. A high resolution finite volume essentially non-oscillatory(ENO) schemes are used along with nonreflecting characteristic boundary conditions that are crucial to screech tone computations to accurately capture the sound waves, shock-cell structures, unsteady shock motions and large-scale instability waves.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.716-724
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• 1990

Oblique impinging plane jets were investigated experimentally and numerically at Reynolds number 21000. The inclination angle was varied from 90.deg.(normal to the impinging plate) to 60.deg.. The distance H between the nozzle exit and the stagnation point on the impinging plate was fixed at H/D=8. The working fluid was air. The mean velocity components and turbulent quantities were measured by a hot-wire anemometer. And the static pressure distributions on the impinging plate were measured by a Pitot tube. In numerical computation, the governing partial differential equations of elliptic type were solved with conventional k-.epsilon. turbulence model. The measurements show that, after impingement, the jet half width alone the wall increases in both directions, and that similarity for each turbulent quantity such as Reynolds shear stress or turbulent kinetic energy is revealed in the wall jet region. The computed results show some deviation from experimental data in the impingement region, where streamline curvature is significant. However, the computed results agree qualitatively well with measurements.

• The KSFM Journal of Fluid Machinery
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• v.15 no.1
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• pp.5-12
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• 2012

In this paper, the heat transfer coefficient measurement techniques using TSP(temperature sensitive paint) were introduced and the results of a comparative study on the heat transfer coefficient measurement by steady state and transient TSP techniques were discussed. The distributions of heat transfer coefficient by a single $60^{\circ}$ inclined impingement jet on a flat surface were measured by both techniques. Tested Reynolds number based on the jet diameter (d) was 30,000 and the distance between jet exit and target plate (L) was fixed at 10d. Results showed that the measured Nusselt number by both techniques indicated significant difference except near the center of impingement jet. Also, the heat transfer coefficients measured by the transient TSP technique were affected by the reference temperature of the jet. Based on the measured data, characteristics of both TSP techniques were analyzed and suggestions for applying them were also given.

• Journal of the Korean Society of Combustion
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• v.17 no.4
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• pp.30-37
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• 2012

The flame lengths and NOx emission characteristics of syngas $H_2$/CO turbulent non-premixed jet flames were investigated. The flame length which is the main parameter governs NOx emission was studied for various syngas compositions. The flame length was compared with previous correlation between Froude number and flame height and it shows that they have good agreements. It was confirmed that the turbulent jet flames herein investigated are in the region of buoyancy-momentum transition. NOx emission was reduced with increased Reynolds number and CO contents in syngas fuel and with decreased fuel nozzle diameter which is attributed by decreased flame residence time. Previous EINOx scaling based on flame residence time of $L_f^3/(d_f^2U_f)$ satisfies only the jet flame in momentum-dominated region, not buoyancy-momentum transition region. The simplified flame residence time ($L_f/U_f$) was adopted in modified EINOx scaling. The modified scaling satisfies the jet flames not only in momentum-dominated region but in buoyancy-momentum transition region. The scaling is also satisfied with $H_2$/CO syngas jet flames.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.272-277
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• 2000

The heat transfer characteristics of confined turbulent slot jet impingement on the flat plate with square rods(turbulence promoter) have been experimentally investigated at different nozzle configuration. The effects of jet Reynolds number (Re=3900, 5800, 7800, 9700), dimensionless slot-to-plate distance(H/B=4, 6, 8) and clearance(c) between square rods and the plate were examined. Measurement of heat transfer rate were conducted using naphthalene sublimation technique. When square rods were inserted over the heat transfer surface, heat transfer rate was slightly increased in the wall jet region and the sharp-edged orifice nozzle was heigher than squared orifice nozzle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.561-567
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• 2005

The effect of triangular multi-tabs attached at the perimeter of jet nozzle on flow structure in the near field was investigated experimentally. A stereoscopic PIV(SPIV) system was employed to measure three orthogonal velocity components of the 3-D turbulent jet. In this study, two different types of sharp-edged jet nozzle having 4, 8 tabs were tested at the Reynolds number of Re=10,000. SPIV measurements were carried out at 5 cross-sectional planes. Six hundred instantaneous velocity fields were measured for each experimental condition and they were ensemble averaged to get spatial distributions of turbulent statistics such as mean velocity and turbulence intensity. Entrainment rate of surrounding fluid into the tabbed jets was estimated using the measured 3-D velocity field data. The strong vortex structure was induced for the jet flow with 4 tabs, increasing entrainment rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.459-466
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• 2000

Flow characteristics of turbulent elliptic jets were experimentally investigated using a single-frame PIV system. A sharp-edged elliptic nozzle with aspect ratio(AR) of 2 was tested and the experimental results were compared with those of circular jet having the same equivalent diameter($D_e$). The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter was about $1{\times}10^4$. The spreading rate along the major and minor axis are different remarkably. The jet half width along the major axis decreases at first and then increases with going downstream. But along the minor axis the jet width increases steadily. The elliptic jet of AR=2 has one switching points at $X/D_e=2$ within the near field. Turbulence properties are also found to be significantly different along the major and minor axis planes.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.119-124
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• 2000

The heat transfer characteristics of confined turbulent slot jet impingement on the flat plate with square rods(turbulence promoter) have been experimentally investigated. The effects of jet Reynolds number (Re=3900, 5800, 7800, 9700), dimensionless slot-to-plate distance(H/B=4, 6, 8) clearance(c) between square rods and the plate, and the length(d) of a side of the square rod were examined. Measurement or heat transfer rate were conducted using naphthalene sublimation technique. When square rods were inserted over the heat transfer surface, heat transfer rate was slightly increased in the wall jet region.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.39-47
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• 2019

Impingement cooling utilizing synthetic jets is emerging as a popular cooling technique because of its high local cooling efficiency. The interaction between the vortex structure of the synthetic jet and the surface is crucial in understanding the mechanism of this technique. In this study, the impinging vortex structure and its advection are investigated by experiments with jet-to-surface spacing $2{\leq}H/D{\leq}7$, and synthetic jet Reynolds number $5120{\leq}Re{\leq}9050$. Using phase-locked particle image velocimetry, ensemble averaged (phase averaged) flow fields are obtained, and vortex identification and quantification techniques are applied. The shape, trajectory, and intensity change of the vortex are assessed. A sharp decline in the vortex intensity and the occurrence of a counter-rotating vortex at the impingement point are observed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.112-119
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• 1995

Measurements of the local heat transfer coeffcients on a spherically concave surface with a round impinging jet are presented. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers used were 1,000, 23,000 and 50,000 and the nozzle-to-jet distance was L/d=2, 4, 6, 8, 10. Presented results are compared to previous measurements for flat plate. In the experiment, the local heat transfer Nusselt numbers on a concave surface are higher than those on a flat plate. Maximum Nusselt number at all region occured at L/d=6 and second maximum in the Nusselt number occured at R/d=2 for both Re=50,000 and Re=23,000 in case of L/d=2 and for only Re=50,000 in case of L/d=4. All other cases exhibit monotonically decreasing value of the Nusselt number along the curved surface.