• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.28-28
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• 1998

단일 충돌제트의 경우 충돌면에서의 열전달 효과는 제트 출구와 충돌면 사이의 간격, 노즐 형상에 따른 제트출구의 초기조건, Re$_{D}$수 변화와 충돌면의 형상이나 표면거칠기 등에 따라 변화하게 된다. 그러나 수직 충돌제트의 경우 정체영역에서의 국소적인 열전달 향상은 용이하나 반경 방향으로 열전달이 점차 감소하게 된다. 따라서 충돌면의 전반적인 열전달 향상을 위해서는 열전달이 정체점보다 상대적으로 낮은 영역에서 열전달 향상이 필요하다. 또한, 실제 적용시 충돌면의 형상이나 협소한 공간에서 노즐위치의 제약으로 인하여 충돌제트가 수직으로 분사되는 경우보다 경사진 제트가 더욱 많이 응용된다. 더욱이, 수직충돌제트가 사용되는 많은 상황에서도 주위의 다른 공기 흐름의 영향으로 인하여 실제 제트가 경사각을 갖고 분사되어진다 이러한 경사충돌제트의 중요성에도 불구하고 경사충돌제트에 대한 연구는 수직충돌제트에 대한 연구보다 상대적으로 적게 이루어져 왔다.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.83-93
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• 2017

A numerical analysis is made of the fluid flow and heat transfer characteristics in the corrugated structure that traps the spent air in the corrugations between impinging jets to reduce crossflow effects on downstream jets in the array. All computations are performed by considering three-dimensional, steady state, and incompressible flow by using the ANSYS-CFX 15.0 code. Averaged jet Reynolds number is 10,000. The oblique angles of impingement jets on the spanwise section are $70^{\circ}$, $80^{\circ}$, $90^{\circ}$, and the oblique angles of impingement jets on the streamwise section are $70^{\circ}$, $90^{\circ}$, $110^{\circ}$. The investigation focuses on the oblique angle influence of impinging jet array on the fluid flow and heat transfer characteristics of a corrugated structure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.32-32
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• 1999

초음속 과소 팽창 제트가 경사진 평판에 충돌을 하게 되면 평판의 표면과 노즐출구에서 팽창된 자유제트(Free jet)와의 상호 간섭으로 인해 매우 복잡한 유동 구조가 형성된다. 예를 들면, 수직평판에서 발생되는 판 충격파(Plate shock)는 경사평판에서는 Upper plate shock, Lower plate shock, Intermediate plate shock과 같이 여러 형태로 발생되어 평판에서의 압력분포에 있어 수직일 경우와 다소 다른 경향을 보여준다. 본 연구의 주요 목적은 평판의 경사각을 변화시킬 때 평판 표면에서의 복잡한 유동 현상을 이해하는데 있다.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.34-40
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• 1999

An experimental study has been conducted to determine the effects of inclined impinging jet on the local heat transfer coefficients. A single jet with nozzle diameter of 24.6 mm was tested for Reynolds numbers from 10,000 to 70,000 and nozzle-to-plate spacings of 2~6 jet diameters. The angle of inclination of the impingement surface relative to the horizontal surface was varied from $0^{\cire}$ (normal impingement) to $60^{\cire}$. The results indicate that the point of maximum heat transfer is moved up from the geometrical stagnation point of inclined surface by Coanda effect. The local heat transfer coefficients on the minor jet region decrease more rapidly than on the major jet region, thus creating an imbalance in the cooling capabilities on the two sides.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.31-31
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• 2000

초음속 충돌제트(impinging jet)의 열 및 운동량 전달(heat and momentum transfer)은 로켓의 이ㆍ착륙, 다단 로켓의 분리, 로켓의 방향조절을 위해 배기 노즐에 부착되는 제트 베인(jet vane)이나 스포일러 탭(spoiler tab), 수직/단거리 이착륙기의 발진, 미사일 발사시스템, 전투기 동체, 날개, 후미 부분에서 발사되는 미사일의 배기가스가 주변장치 등에 충돌할 때 발생되는 문제점 등을 사전 예측하여 관련장비의 설계 둥에 유용한 자료로 이용된다. 따라서 이에 대한 기초 연구로서 초음속 유동 실험장치를 이용하여 마하수(Mach Number) 1.0 및 1.8인 경우에 대하여 수직/경사평판에서 팽창 비, 거리, 경사각에 따른 충돌 면에서의 단열 벽면온도를 측정하였다. (중략)

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.67-74
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• 1999

Problems created by supersonic jet impinging on solid objects or ground arise in a variety of situations. For example multi-stage rocket separation, deep-space docking, V/STOL aircraft, jet-engine exhaust, gas-turbine blade, terrestrial rocket launch, and so on. These impinging jet flows generally contain a complex structures. (mixed subsonic and supersonic regions, interacting shocks and expansion waves, regions of turbulent shear layer) This paper describes experimental works on the phenomena (surface pressure distribution, flow visualization) when underexpanded supersonic jets impinge on the perpendicular, inclined plate using a supersonic cold-(low system. The used supersonic nozzle is convergent-divergent type, exit Mach number 2, The maximum on the plate when it was inclined was much larger than perpendicular plate, owing to high pressure recoveries through multiple shocks. Surface pressure distribution as to underexpanded ratio showed similar patterns together.

• 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.

• 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.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.3
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• pp.10-19
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• 1998

When an under-expanded supersonic jet impinges on an inclined flat surface, a complex flow structure is established due to the intersection between the flat surface and the shock system of the free jet. This study reports on an experimental results of flows due to under-expanded axisymmetric sonic jets impinging on flat plate. Plate inclination from $60^{\cire}$~$90^{\cire}$ were investigated by means of detailed measurements of the surface pressure and schlieren photograph and surface flow visualization. The schlieren photograph are consistent with the pressure distribution and the surface flow visualization pictures are clearly related to the pressure distributions. The maximum wall pressure is found to be large on the inclined plate than on the perpendicular plate.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.113-118
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• 2004

Experiments are conducted to get basic information of under-expanded impinging jet in the near field. Experimental parameters are impinging angle and under-expanded ratio. As the under-expanded ratio increases, the maximum surface pressure decreases and the reducing effect of recovery factor increases. As the impinging angle decreases, the peak of surface pressure is displaced slightly from the geometric center of the plate to the upward region and the cooling region is expanded in the downward region, whereas it is contracted in the upward region.