• Journal of Advanced Marine Engineering and Technology
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• 제22권5호
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• pp.588-594
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• 1998

Heat transfer characteristics of distance between impinging surface and a plane jet were experi-mentally investigated. The local heat transfer coefficients were measured by a thermochromic liq-uid crystal(TLC) The jet Reynolds number studied was varied over the range from 10,000310 to 30,000310 the nozzle-to-plate distance (H/B) from 4 to 10. It was observed that the Nusselt number increases with Reynolds number the occurrence of the secondary peak in the Nusselt number is within the potential core region the potential core of the jet flow can reach the impinging surface so that the wall jet can a transition from laminar to turbulent flow resulting in a sudden increase in the heat transfer rate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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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.

• 대한기계학회논문집
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• 제11권2호
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• pp.214-221
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• 1987

본 논문에서는 2차원충돌분류에서 사각리브(rib)를 갖는 요철형전열면에 대한 실험에 관한 것이며, 리브의 높이를 (ｅ=5nm) 일정하게 하고 리브의 피치(ｐ=25,35,50 nm) 변화, 노즐출구와 전열면간 거이(H/B=1~14) 및 노즐출구유속(ｕ$_{e}$=12.30~ 18.07m/s)의 변화에 따른 전열특성을 실험적으로 구명하고 평판전열면의 경우와 비교 검토한다. 또한 스모크와이어(smoke-wire)법으로 평판 및 리브판에서의 유체의 거동 을 가시화하여 전열기구의 정성적 특성을 검토하는데 목적이 있다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1999년도 제13회 학술강연논문집
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• pp.33-33
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• 1999

The Coanda effect is the tendency for a fluid jet to atach itself to an adjacent surface and follow its contour without causing an appreciable flow separation. The jet is pulled onto the surface by the low pressure region which develops as entrainment pumps fluid from the region between the jet and the surface. Then the jet is held to the wall surface by the resulting radial pressure gradient which balance the inertial resistance of the jet to turning. The jet may attach to the surface and may be deflected through more than 180 dog, when the radius of the Coanda surface is sufficiently large compared to the height of the exhaust nozzle. However, if the radius of curvature is small, the jet turns through a smaller angle, or may not attach to the surface at all. In general, the limitations in size and weight of a device will limit the radius of the deflection surface. Thus much effort has been paid to improve the jet deflection in a variety of engineering fields. The Coanda effect has long been applied to improve aerodynamic characteristics, such as the drag/lift ratio of flight body, the engine exhaust plume thrust vectoring, and the aerofoil/wing circulation control. During the energy crisis of the seventies, the Coanda jet was applied to reduce vehicle drag and led to drag reductions of as much as about 30% for a trailer configuration. Recently a variety of industrial applications are exploiting another characteristics of the Coanda jets, mainly the enhanced turbulence levels and entrainment compared with conventional jet flows. Various industrial burners and combustors are based upon this principle. If the curvature of the Coanda surface is too great or the operating pressure too high, the jet flow will break away completely from the surface. This could have catastrophic consequences for a burner or combustor. Detailed understanding of the Coanda jet flow is essential to refine the design to maximize the enhanced entrainment in these applications.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1277-1289
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• 1998

The objective of the present study is to investigate experimentally the mean flow characteristics of the three-dimensional turbulent boundary layer over a rotating disk with an impinging jet at the center of the disk, which may be regarded as one of the simplest models for the flow in turbomachinery. A relatively strong radial outflow (crossflow) generated from the impinging jet is added to the radial outflow (crossflow) induced by the centrifugal force in order to create the three-dimensional boundary layer. A new calibration technique has been introduced to determine the velocity direction and magnitude using an I-wire probe, where the uncertainties are ${\pm}1.5^{\circ}$ and ${\pm}0.35\;m/s$, respectively, in the laminar boundary layer region, compared with the known exact solutions. The flow in the tangential direction is of similar type to that associated with a favorable pressure gradient, considering that no wake region appears in wall coordinate velocity profiles and the Clauser shape factor is between 4.0 and 5.3. The flow angle is significantly changed by the crossflow generated by the impinging jet.

• 에너지공학
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• 제21권2호
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• pp.187-193
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• 2012

본 연구의 목적은 벽면제트영역의 열전달증진을 위해 직삼각형 로드 및 정사각형 로드를 충돌판앞에 배열한 후 로드와 충돌판 사이의 간극을 변화시키면서 열유동 특성을 실험적으로 검토한 것이다. 열전달증진율은 천이영역인 H/B=10보다는 포텐셜코어영역인 H/B=2에서 더 높게 나타났다. 본 실험범위에서 최대 열전달증진율은 직삼각형 로드를 설치할 때(H/B=2, C=1mm인 조건) 로드가 없는 평판과 비교하면 평균 약 46% 높게 나타났다. 그리고 직삼각형 로드와 정사각형 로드의 열전달증진율을 비교하면 간극 변화와 관계없이 직삼각형 로드가 정사각형 로드보다 평균 약 3~8% 정도 높게 나타났다.

• Wind and Structures
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• 제9권6호
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• pp.419-440
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• 2006

This article synthesizes the literature on the meteorology, experimental simulation, and wind engineering ramifications of intense downburst outflows. A novel design of a large-scale test facility and experimental evidence of its validity are presented. A two-dimensional slot jet is used to simulate only the outflow region of a downburst. Profiles of mean velocity and turbulence quantities are acquired using hot-wire anemometry. Comparison with the literature provides empirical evidence that supports the current approach. A geometric analysis considers the validity of applying a two-dimensional approximation for downburst wind loading of structures. This analysis is applicable to power transmission lines in particular. The slot jet concept can be implemented in a large boundary layer wind tunnel to enable large-scale laboratory experiments of thunderstorm wind loads on structures.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.136-142
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• 1997

The present study is aimed to investigate flow characteristics of confined jet flow within circular pipe. Numerical method based upon revised SOLA scheme which secures conservation form of convective terms on irregular grids by interpolating the variables appearing in staggered meshes is adopted on cylindrical coordinate formation. Computation was carried out for two kinds of Reynolds number, $10^5\;and\;1.5{\times}10^5$ defined by diameter of outer pipe and time-mean driving jet velocity. Results show that periodic vortex shedding from the jet mixing layer is profound and related unsteady flow characteristics prevail over the entire region. Spatial distribution of pressure and kinetic energy, fluctuation of static wall pressure, together with radial velocity components are examined in terms of instantaneous and time-mean point of views.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.29-34
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• 2002

TIn this study, the counter-jet flows which designed for improvement of aerodynamic performance of the blunt body vehicle have been analyzed. The variations of the drag force and jet penetration depth due to changes in the stagnation properties of counter jet new such as total pressure, mach number, and total temperature. The counter jet flow, which is injected toward incoming supersonic freestream at stagnation region of blunt cone-cylinder vehicle, have been studied by using upwind flux difference splitting navier-stokes method. The changes in the stagnation pressure and Mach number resulted in large effects on the wall pressure and drag force, on the other hand tile total temperature changes did not.

• 한국항공우주학회지
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• 제33권4호
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• pp.79-84
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• 2005

평판 표면에 충돌하는 축대칭, 과소팽창 제트에 대한 실험적 연구가 수행되어졌으며, 벽압력 및 단열 벽온도 분포가 자세히 측정되어졌다. 벽온도 분포 결과에 대한 설명을 위하여 자유제트 내에서의 전온도 값을 전온도 탐침을 사용하여 측정하였다. 본 연구에서 실험 변수로는 과소팽창비와 노즐-평판간 거리가 고려되었다. 노즐-평판 간 거리에 따라 제트 경계 및 충돌면에서의 에너지 박리에 의해 서로 다른 형태의 단열 벽온도 분포가 나타났으며, 과소팽창비가 큰 경우, 중심영역에서의 저온 유체 입자의 고립효과로 정체점의 회복계수가 크게 낮아지는 현상 또한 관찰되었다.