• 한국분무공학회지
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• 제4권1호
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• pp.55-61
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• 1999

The first maximum point in the stability curve of liquid jet, i.e., the critical point is associated with the critical Reynolds number. This critical Reynolds number should be predicted by simple means. In this work, the critical Reynolds number in the stability curve of liquid jet are predicted using the empirical correlations and the experimental data reported in the literatures. The critical Reynolds number was found to be a function of the Ohnesorge number, nozzle lengh-to-diameter ratio, ambient Weber number and nozzle inlet type. An empirical correlation for the critical Reynolds number as a function of the Ohnesorge number and nozzle length-to-diameter ratio is newly proposed here. Although an empirical correlation proposed in this work may not be universal because of excluding the effects of ambient pressure and nozzle inlet type, it has reasonably agrees with the measured critical Reynolds number.

• 한국가시화정보학회지
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• 제6권1호
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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.

• 대한기계학회논문집
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• 제19권8호
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• pp.1940-1949
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• 1995

A numerical study for a two dimensional multi-jet with crossflow of the spent fluid has been carried out. Three different distributions of mass-flow rate at 5 jet exits were assumed to see their effects upon the flow characteristics, especially in the jet-flow region. For each distribution, various Reynolds numbers ranging from laminar to turbulent flows were considered. Results show that a fully developed laminar flow exists above a certain Reynolds number whose exact value depends upon the mass flow rate distribution. AS the Reynolds number increases, the flow becomes transitional from downstream and finally a fully developed turbulent flow forms in the jet-flow region. The critical Reynolds number where the fully developed turbulent flow forms is quite dependent upon the distribution of mass-flow rate. One interesting result is that the distribution of the skin friction coefficient along the inpingement plate in the jet-flow region shows a consistent dependency on the Reynolds number, i.e. inversely proportional to the square root of the Reynolds number, regardless of flow regime.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2005년도 추계학술대회 논문집
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• pp.23-27
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• 2005

The flow characteristics in a confined slot jet impinging on a flat plate were Investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using cinematic Particle Image Velocimetry technique.

• 한국가시화정보학회지
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• 제3권2호
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• pp.57-62
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• 2005

The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using proper orthogonal decomposition.

• 한국분무공학회지
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• 제4권2호
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• pp.47-52
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• 1999

The prediction of the critical Reynolds number in the stability curie of liquid jet was mainly analyzed by the empirical correlations and the experimental data through the literature. The factors affecting the critical Reynolds number include Ohnesorge number, nozzle length-diameter ratio, ambient pressure and nozzle inlet type. The nozzle inlet type was divided into two groups according to the dependence of the critical Reynolds number on the length-to-diameter ratio of nozzle. The empirical correlations for the critical Reynolds number as a function of above factors mentioned are newly proposed.

• 설비공학논문집
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• 제10권5호
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• pp.509-522
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• 1998

An experimental investigation is reported on the heat transfer coefficient from a rotating flat plate in a round turbulent normally impinging water jet. Tests were conducted over a range of jet flow rates, rotational speeds, jet radial posetions with various combinations of three jet nozzle diameter. Dimensionless correlation of average Nusselt number for laminar and turbulent flow is given in terms of jet and rotational Reynolds numbers, dimensionless jet radial position. We suggested various effective promotion methods according to heat transfer characteristics and aspects. The data presented herein will serve as a first step toward providing the information necessary to optimize in rational manner the cooling requirement of impingement cooled rotating machine components.

• Journal of Biosystems Engineering
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• 제20권1호
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• pp.66-72
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• 1995

A numerical study for a two dimensional multi-impingement jet with crossflow of the spent fluid has been carried out. To study the flow characteristics especially in the jet flow region, three different distributions of mass flow rate at 5-jet exits were assumed. For each distribution, various Reynolds numbers ranging from laminar to turbulent flows were considered. Calculations drew the following items as conclusion. 1) A periodical fully developed flow was observed from the third protrusion. This was also observed from previous experimentally by Whidden at al. The Nessult number at the protrusion surface increased mildly as going downstream. 2) The low Reynolds number turbulence model of Launder and Sharma was found to be adequate for the prediction of fluid flow and heat transfer characteristics of two dimensional multi-jet configuration. 3) The Nusselt number at the protrusion surface was nearly proportional to the square root of the Reynolds number.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.55-58
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• 2006

The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The three different kinds of confined slot were applied to the jet with a view to evaluating the shape effect and the jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. It was found that the vortex structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Finally, the slot shape was proved to be related with the generation timing of vortex pair and the temporal vortex structure.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.241-244
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• 2002

Large eddy simulation of a circular jet at the Reynolds number of 10000 is performed to investigate turbulence suppression effect with single frequency excitation at the non-dimensional frequency of 0.017. Instantaneous flow fields show that, with excitation, naturally occurring energetic vortices are suppressed through earlier saturation and breakdown of the shear layer vortices into fine grained turbulence. Due to the excitation, the Reynolds stresses are larger for the excited case near the jet and turbulence suppression begins afterward. The Reynolds normal stresses show largest suppression in the shear layer near the jet and in the centerline further downstream, while the Reynolds shear stress shows largest suppression in the shear layer at all the downstream locations.