• 한국분무공학회지
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• 제10권4호
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• pp.26-31
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• 2005

Today, the research to examine a fact that interaction between the air and the fluid free surface affects the steady state flow and air. We proved the interaction between vortex pairs and free surface on each condition that is created by the end of delta wings. Another purpose of this study is to investigate the effect of surface active material which call change the surface tension and we must consider when we refer to turbulent flow on surface tension. Therefore, this research examined the growth process of vortex pairs on condition of clean, contaminated free surface and wall after we made vortex pairs through counter rotating flaps. The results of this study suggest that vortex pairs in clean free surface rise safely but the vortex pairs in contaminated free surface and rigid, no slip is made secondary vortex or rebounding. However the secondary vortex in rigid, no slip is stronger than before. and we can find the vortex shape which roll up more completely. However, these will disappear by the effect of wall.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.67-72
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• 2002

Today, the research to examine a fact that interaction between the air and the fluid free surface affects the steady state flow and air. We proved the interaction between vortex pairs and free surface on each condition that is created by the end of delta wings. another purpose of this study is to investigate the effect of surface active material which can change the surface tension and we must consider when we refer to turbulent flow on surface tension. therefore, this research examined the growth process of vortex pairs on condition of clean, contaminated free surface and wall after we made vortex pairs through counter rotating flaps. The results of this study suggest that vortex pairs in clean free surface rise safely but the vortex pairs in contaminated free surface and rigid, no slip is made secondary vortex or rebounding. However the secondary vortex in rigid, no slip is stronger than before, and we can find the vortex shape which roll up more completely. However, these will disappear by the effect of wall.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.627-632
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• 2000

Developing turbulent flows in a rotating 90 degree bend with square cross-section were measured by a hot-wire anemometer. The six orientation hot-wire technique was applied to measured the distributions of 3 mean velocities and 6 Reynolds stress components. Effects of Coriolis and centrifugal forces caused by the curvature and rotation of bend on the mean motion and turbulence structures were experimentally investigated Productive addition of Coriolis and centrifugal forces to the outward radial direction in the entrance region of bend increases the secondary flow intensity according to the rotational speeds. However, after 45 degree of bend, centrifugal force due to the rotation of bend may promote the break down of counter rotating vortex pair into multi-cellular pattern, thereby decreasing the production rate of turbulence energy and Reynolds stresses.

• 대한기계학회논문집B
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• 제26권2호
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• pp.261-268
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• 2002

Turbulent flow past a square cylinder confined in a channel is numerically investigated by Large Eddy Simulation(LES). The main objectives of this study are to verify the experimental results of Nakagawa et al.[Exp. in Fluids, Vol. 27, 3, pp. 284∼294, 1999] by LES and to obtain related flow information in detail. The LES results obtained are in excellent agreement with the experiment both qualitatively and quantitatively. The passive paticles numerically released into the flow field clearly show the barman vortex street. However, the vortices shed from the cylinder are significantly affected by the presence of the plates. Futhermore, periodic and alternating vortex-rollups are observed in the vicinity of the plates. The rolled-up vortex is convected downstream together with the corresponding Karman vortex forming a counter-rotating vortex pair. It is also revealed that the cylinder greatly enhances mixing process of the flow.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.117-124
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• 2004

The mixing enhancement is one of the most important problems for the development of scramjet engines. The influence of the streamwise vortices produced by a ramp in a unheated supersonic flow on the mixing of twin jets injected from its base was experimentally investigated. Nominal Mach number of the main airstream and of the twin jets at the nozzle exits were 2.35 and 2.0, respectively. Three dimensional velocity distributions near the ramp with and without injection were measured by Particle Image Velocimetry (PIV). A pair of counter rotating streamwise vortices could be seen behind the injector without injection. On the other hand, two pairs of streamwise vortices could be seen with injection. The outer one had the same direction as the vortex pair produced by the ramp, but they were stronger than those produced by the ramp. The inner ones had the opposite directions to the outer ones. It is considered that these vortices enhance the mixing near the injector.

• 한국해안해양공학회지
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• 제13권2호
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• pp.109-121
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• 2001

잠재된 평판 방파제가 해수 교환에 미치는 영향을 실험적으로 조사하였고 그 결과를 제시한다. 흐름은 PIV 시스템으로 관측되었으며 조화분석으로부터 분리된 평균 흐름과 파랑 타원이 각각 제시된다. 실험결과, 순환유량은 입사파의 체적플럭스와 밀접한 관계가 있으며 쌍와류가 평판 후면에서 관측되었다. 염료추적에 의하면 평판위에서 발생된 제트류로 인한 난류의 영향으로 유입되는 해수와 항내 오염물질이 상당히 잘 섞이고 있음을 보여주고 있다.

• 대한기계학회논문집B
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• 제26권1호
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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.

• 대한기계학회논문집B
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• 제28권7호
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• pp.834-841
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• 2004

Experimental study on the three-dimensional topology of hairpin packet structures in turbulent boundary layers were carried out. Two different Reynolds number based on momentum thickness, Re$\sub$$\theta$/=514 and 934 were generated in a blowing type wind tunnel under the condition of zero pressure gradient. Simultaneous measurements of velocity fields at a wall-normal plane and wall-parallel plane by a plane PIV and a Stereo-PIV systems. The two Nd:Yag laser systems and three CCD cameras were synchronized to obtain instantaneous velocity fields at the same time. To avoid optical noise at the crossing line by the two laser light sheets, a new optical arrangement using polarization was applied. The obtained velocity fields show the existence of hairpin packet structure vividly and the idealized hairpin vortex signature is confirmed by experiment. Two counter-rotating vortex pair which reflects the cutting plane of hairpin legs are found both side of a strong streaky structure when the wall-normal plane cuts the hairpin head.

• 대한기계학회논문집B
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• 제20권4호
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• pp.1363-1375
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• 1996

Oil-film flow visualizations and three-dimensional flow measurements using a five-hole probe have been conducted to investigate three-dimensional flow characteristics and total pressure losses of a row of film-cooling jets injected in spanwise direction. For several span-to-diameter ratios, experiments are performed in the case of three velocity ratios of 0.5, 1.0 and 1.5. The flow measurements show that downstream flow due to the injection is characterized by a single streamwise vortex instead of a pair of counter-rotating vortices, which appear in the case of streamwise injection, and the vortex strength strongly depends on the velocity ratio. Regardless of the velocity*y ratio, presence of the spanwise film-cooling jets always produces total pressure loss, which is pronounced when the velocity ratio is large. It has also been found that the production of the total pressure loss is closely related to the secondary vortical flow. In addition, effects of the span-to-diameter ratio on the flow and total pressure loss are discussed in detail.

• 대한기계학회논문집B
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• 제28권5호
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• pp.612-618
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• 2004

Stereoscopic PIV measurements were made in the wind tunnel with the actual size waterjet model. The main wind tunnel provides the vehicle velocity while the secondary wind tunnel adjusts the jet issuing velocity. Experiments were performed at the range of jet to vehicle velocity ratio (JVR), 3.75 to 8.0 and the Reynolds number of 220,000 based on the jet velocity and the hydraulic diameter of the waterjet intake duct. Wall pressure distributions were measured for various JVRs. Three dimensional velocity fields were obtained at the inlet and outlet of the intake duct. It is found that severe acceleration is occurred at the lip region while deceleration is noticeable at the ramp side. The detailed three dimensional velocity fields can be used as the accurate velocity input for the CFD simulation. It is interesting to note that there are many different types of vortices in the instantaneous velocity field. It can be considered that those vortices are generated by the corner of rectangular section of the intake and Gortler vortices due to the curved wall. However, typical secondary flow with a pair of counter rotating vortex pair is clearly seen in the ensemble averaged velocity field.