• Journal of the Korean Society of Visualization
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• v.6 no.1
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• pp.34-40
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• 2008

The flow characteristics in a confined slot jet impinging on a flat plate were investigated in low Reynolds number regime (Re$\leq$1,000) by using time-resolved particle image velocimetry technique. The jet Reynolds number was varied from 404 to 1026, where it is presumed that the transient regime exists. It is found that the vortical structures in the shear layer are developed with increasing Reynolds number and that the jet remains steady at the Reynolds number of 404. Vortical structures and their temporal evolution are verified and the results were compared with previous numerical studies.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.4
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• pp.371-380
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• 2000

The turbulent heat transfer from a round oblique impinging jet on a concave surface were experimentally investigated. The transient measurement method using liquid crystal was used in this study. In this measurement, a preheated wall was suddenly exposed to an impinging jet while recording the response of liquid crystals to measure surface temperature. The Reynolds numbers were 11000, 23000 and 50000, nozzle-to-surface distance ratio was from 2 to 10 and the surface angles were a =$0^{\circ}\;15^{\circ},\;30^{\circ}and\;40^{\circ}$. Correlations of the stagnation point Nusselt numbers with Reynolds number, jet-to-surface distance ratio and dimensionless surface angle, which account for the surface inclined angle, are presented. The maximum Nusselt numbers, in this experiment, occurred in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. In this experiment, the maximum displacement is about 0.7 times of the jet nozzle diameter when surface curvature, D/d is 10.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.2
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• pp.105-110
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• 2004

The objective of this study is to obtain the instability characteristics of the plane jet impinging on circular cylinder associated with the cylinder-tone. It is found that the characteristics depends upon he ratio of the cylinder diameter to the nozzle width, D/h, and the jet velocity. When the ratio is oderate the cylinder-tone is similar to the edge-tone. With increase of the ratio, its characteristics ecomes similar to that of the plate-tone in which only the high-speed tone associated with turbulent et is generated. When D/h 〈1. the frequency range, especially the lower limit of frequency, is ignificantly influenced by the cylinder diameter. At around D/h = 1/2, while low speed tones are nduced with the antisymmetric mode of instability and affected by the vortex shedding from the ylinder, high-speed tones are generated, at first, with the symmetric mode of instability. and then, ith antisymmetric mode, as the jet velocity increases.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.508-513
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• 2003

Experiments are performed to investigate the detailed structure of underexpanded twin jet impinging on a perpendicular flat plate. The major parameters, such as nozzle operating pressure and nozzle spacing, are varied to create different jet flow fields resulted from the complicated interactions of the twin jets. From the surface pressure measurements and shadowgraphs taken by schlieren optical system, the jet structure is strongly dependent on the nozzle operation pressure and the spacing. The results obtained show that the closer nozzle spacing may induce to decrease the diameter of the Mach disk within the first shock cell in the underexpanded twin jet. With the increasing nozzle operating pressure and decreasing the nozzle spacing, a new shock wave appears at the entrainment region between the two jets, due to the enhancement of mixing effect of the both jets. The closer nozzle spacing makes the overall impinging pressure level higher, while severe pressure oscillation along the axis of symmetry. Furthermore it is recommended the wider spacing to obtain higher thrust under the present experimental conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.768-773
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• 2004

When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is underexpanded. If a flat plate is placed normal to the jet at a certain distance from the nozzle, a detached shock wave is formed at a region between the nozzle exit and the plate. In general, supersonic moist air jet technologies with nonequilibrium condensation are very often applied to industrial manufacturing processes. In spite of the importance in major characteristics of the supersonic moist air jets impinging to a solid body, its qualitative characteristics can not even know. In the present study, the effect of the nonequilibrium condensation on the underexpanded moist air jet impinging on a vertical flat plate is investigated experimentally. Flow visualization and impact pressure measurement are performed for various relative humidities and flat plate positions. The obtained results show the plate shock and Mach disk are dependent on the nozzle pressure ratio and the relative humidity, but for a given nozzle pressure ratio, the diameters of the plate shock and Mach disk depend on the stagnation relative humidity. The impact pressure deviation from the flow of without condensation is large, as the relative stagnation humidity increases.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.239-246
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• 2010

When galvanized steel strip is produced through a continuous hot-dip galvanizing process, the thickness of the adhered zinc film is controlled by impinging a thin plane nitrogen gas jet. The thickness of the zinc film is generally affected by impinging pressure distribution, its gradient and shearing stress at the steel strip. These factors are influenced by static pressure of gas spraying at air knife nozzle, a nozzle-to-strip distance and strip and a geometric shape of the air knife, as well. At industries, galvanized steel strip is produced by changing static pressure of gas and a distance between the air knife nozzle and strip based on experimental values but remaining a geometric shape of nozzle. Splashing and check-mark strain can generally occur when a distance between the air knife nozzle and strip is too short, while ability of zinc removal can lower due to pressure loss of impinging jet when a distance between the air knife nozzle and strip is too long. In present study, buckling of the jet and change of static pressure are observed by analyzing flow characteristics of the impinging jet. The distance from the nozzle exit to the strip varies from 6 mm to 16 mm by an increment of 2 mm. Moreover, final coating thickness with change of a distance between the air knife nozzle and strip is compared with each case. An ability of zinc removal with the various distances is predicted by numerically calculating the final coating thickness.

• Journal of the Korean Society of Combustion
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• v.16 no.1
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• pp.15-21
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• 2011

An experimental study was conducted to investigate the flame stability of the synthetic gas (syngas) using an impinging premixed jet burner. Since the syngas mainly consisted of $H_2$ and CO, the $H_2$/CO mixture was simulated as the syngas. $H_2$/CO mixture ratios, fuel/air mixture velocities and equivalence ratios were used as major parameters on the flame stabilitym The role of the impinging plate on the flame stability was also examined. In addition, laminar burning velocities of the $H_2$/CO mixture were predicted numerically to understand the characteristics of the flame stability for the syngas. The increase in the H2 concentration into the syngas brings about the extension of the blowout limit and the reduction in the flashback limit in terms of the stable flame region. The impinging jet plate broadened the blowout limit but does not play important role in changing of the flashback limit. Finally, it was found that the stability region of the flame using the syngas, which is expressed in terms of the mixture velocity and the equivalence ratio in this study, significantly differed from that of $CH_4$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.324-333
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• 1998

Measurements of the local heat transfer coefficients on a hemispherically concave surface with a round oblique impinging jet were made. The liquid crystal transient method was used for these measurements. This method, which is a variation of the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystal for the surface temperature measurements. The Reynolds number used was 23,000 and the nozzle -to -jet distance was L/d=2, 4, 6, 8 and 10 and the jet angle was $\alpha$=0$^{\circ}$, 15$^{\circ}$, 30$^{\circ}$and 40$^{\circ}$. In the experiment, the maximum Nusselt number at all region occurred at L/d(equation omitted)6 and Nusselt number decreases as the inclined jet angle increases. For the normal jet the contours of constant Nusselt number are circular and as the jet is inclined closer and closer to the surface the contours become elliptical shape. The decreasing rate of the Nusselt number at X/d＞ 0(upstream) on a surface curvature are higher than those on a flate plate and the decreasing rate of the Nusselt number at X/d ＜0(downstream) on a surface curvature are lower than those on a flate plate. And also, the decreasing rate of local Nusselt number distribution at X/d ＜0(upstream) exhibit lower than with X/d ＜0(downstream) as jet angle increases. The second maximum Nusselt number occurred at long distance from stagnation point as jet angle increases.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.1
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• pp.37-42
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• 1997

Turbulent flow characteristics of a two - dimensional oblique plate impinging jet(OPIJ) were experimentally investigated. The jet mean velocity and turbulent intensity profIles were also measured along the plate. The jet Reynolds numbers(Re, based on the nozzle width)ranged from 10, 000 to 35, 000, the nozzle - to - plate distance(H/B) from 2 to 16, and the oblique angle (a) from 60 to 90 degree. It has been found that the stagnation point shifted toward the minor flow region as the oblique angle decreases and the position of the stagnation point nearly coin¬cided with that of the maximum turbulent intensity.

• 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.