• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.23-29
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• 2006

In an annular injection supersonic ejector, the supersonic primary flow is injected along the side wall, therefore a funnel-shaped shock wave is generated by the contraction angle of the mixing chamber. In the present study, we developed a simple funnel shock wave model using 2-D wedge and conical shock wave relations. In result, the secondary flow pressure can be predicted more accurately than using a simple 2-D wedge shock wave model. Through the same analysis, the compression ratio and the adiabatic efficiency according to the entrainment ratio were calculated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.470-483
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• 1990

Turbulent jet in a crossflow, issuing from a row of holes on a convex surface of 90 .deg. bend duct, is predicted by a 3-dimensional numerical method. The Cartesian coordinate system in adopted in upstream and downstream tangents and the cylindrical polar coordinate system in curved region. The Reynolds stresses and heat fluxes are obtained from a standard k-e model in the core region and van Driest model in the vicinity of the wall. The governing equations are discretized by a finite volume method and solutions are obtained by a locally elliptic calculation procedure. Pressure and convective terms are treated by SIMPLE algorithm and hybrid scheme respectively. A vortex initially induced by the injected jet has been built up due to the interaction with the secondary flow caused by pressure gradient and centrifugal force. The vortex structure has a strong influence on the wall cooling effectiveness. Another vortex like horseshoe is formed in the vicinity of the injection hole and its strength is getting weak as it moves downward.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1735-1745
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• 1998

Oil-film surface flow visualizations and three-dimensional flow measurements using a straight five-hole probe have been conducted for a circular impinging jet which is normally oriented to the crossflow in a channel. Throughout the experiments, the ratio of channel height to injection hole diameter, H/D, is fixed to be 1.0, and blowing ratio is varied to be 1.0, 2.0, 3.0 and 4.0. From the surface flow visualizations for both top wall(target plate) and bottom wall, impinging jet region on the target plate can be clearly identified, and for the small value of H/D = 1.0, presence of the bottom wall changes the near-hole flow structure, significantly. The three-dimensional flow measurements show that in the dawnstream region of the injection hole, there exist a pair of counter-rotating vortices, called "scarf vortices", and the strength of the vortices strongly depends on the blowing ratio. In addition, a new flow model in the flow symmetry plane has been proposed for H/D = 1.0.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.1
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• pp.125-132
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• 2002

An experimental study on the characteristics of stability of propane turbulent nonpremixed jet flames discharged normal to air free-streams with uniform velocity profile is conducted. Experimental observations are focused on the flame shape, the stability considering two kinds of flame, lift-off distance, and the flame length according to velocity ratio. In order to investigate the mixing structure of the flame base at the lower limit, we employ the RMS technique and measure the species concentration by a gas chromatography. In the results of the stability curve and lifted flame, it is fecund that the dependency of nozzle diameter is closely related to the large-scale vortical structure representing counter-rotating vortices pair. Also, the detailed discussion on the phenomenon of blowout due to this large vortical motion, is provided.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.42-49
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• 2000

A computation using the mass-averaged implicit Wavier-Stokes equations has been applied to solve the flow fields of the supersonic jets normally injected into supersonic freestreams and several types of turbulence model has been employed to close the governing equations. The ratio of the freestream to injection flow total pressures has been varied to elucidate the major characteristics of the mixing flow of the two streams. The freestream Mach number has been varied to investigate some change in the injection flow field. The results show that the positions of the separation and reattachment, locating upstream and downstream of the injection hole respectively, are strongly dependent on the ratio of total pressures and the freestream Mach number.

• The KSFM Journal of Fluid Machinery
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• v.11 no.6
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• pp.64-68
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• 2008

막 냉각 연구를 위해 CFD를 이용할 때 적용 한계 및 그 타당성을 검증하고자 하였다. 이 글에서는 냉각공기공으로부터 분출된 냉각공기가 고온 고속으로 흐르는 주유동과 평판 사이에 벽면을 고온의 가스에 노출되는 것을 막기 위해 위치시킨 막냉각공기 흐름의 형태를 CFD를 이용하여 분석하였다. 모든 경계조건 및 격자계 그리고 검증 단계의 예까지 서술함으로써 이러한 CFD를 이용할 때 유용하게 적용될 방법들을 제공하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.2
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• pp.403-408
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• 2001

The flow characteristics of impinging jet flow are affected greatly by nozzle plate to distance. An sharp edge nozzle was used to achieve uniform mean velocity at the nozzle inlet, and its diameter is 10 mm(d). Therefore, the flow characteristics on the impinging jet plate can be changed largely by the control of main flow. In the parent study, we investigate the effects of main flow length, its variable is nozle plate to distances(12d, 10d, 8d, 6d and 4d)

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.1
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• pp.40-46
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• 2013

Turbulent flow and heat transfer in a channel with a detached rib array have been simulated. The computations are based on the finite volume method with the SIMPLE algorithm. The forms of ribs considered in this study were rib with rectangular cross section, rib with groove, broken rib, and V-shaped rib. The ribs were deployed transverse or aligned $60^{\circ}$ to the main direction of the flow. Local heat transfer coefficients were obtained at various Reynolds numbers within the turbulent flow regime. Area-averaged data were calculated in order to compare the overall performance of the tested ribbed surfaces and to evaluate the degree of heat transfer enhancement induced by the ribs with respect to the smooth channel. The highest heat transfer occurred for the rib with groove which was aligned $60^{\circ}$ to the main flow direction. Performance factor was decreased with the increase of velocity, and it was found that the best performance factor was obtained in the low velocity region.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.1
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• pp.31-40
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• 2000

This paper describes the numerical computations of the interaction between the streamwise vortex and a flat plate 3-D turbulent boundary layer. In the present study, the main interest is in the behavior of the streamwise vortices introduced in turbulent boundary layers. The flow behind a vortex generator is modeled by the information that is avilable from studies on the dalta winglet. An algorithm of the solution of the incompressible Navier-Stokes equations for three-dimensional turbulent flows, together with a two layer turbulent model to resolve the near-wall flow, is based on the method of artificial compressibility. The present results show boundary layer distortion due to vortices, such as strong spanwise flow divergence and boundary thinning, and have a good agreement with the experimental data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.900-915
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• 1988

Velocities and Reynolds stress in the 3-dimensional turbulent flow in a square duct with a 180.deg. bend were measured by hot wire anemometer. Slant wire was rotated to 4 directions and I type wire was rotated to 2 directions and the voltage outputs of them were combined to obtain the mean velocities and Reynolds stresses. In order to increase the accuracy of measurement, mean cubic value as well as mean square value of a voltage fluctuation across hot wire were measured and used to obtain mean velocities and Reynolds stresses. Measured data were compared with Chang et al's experimental data measured by LDV and Launder et al's numerical predictions by ASM, and found to be in good agreement with them.