• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.3
• /
• pp.716-724
• /
• 1990

Oblique impinging plane jets were investigated experimentally and numerically at Reynolds number 21000. The inclination angle was varied from 90.deg.(normal to the impinging plate) to 60.deg.. The distance H between the nozzle exit and the stagnation point on the impinging plate was fixed at H/D=8. The working fluid was air. The mean velocity components and turbulent quantities were measured by a hot-wire anemometer. And the static pressure distributions on the impinging plate were measured by a Pitot tube. In numerical computation, the governing partial differential equations of elliptic type were solved with conventional k-.epsilon. turbulence model. The measurements show that, after impingement, the jet half width alone the wall increases in both directions, and that similarity for each turbulent quantity such as Reynolds shear stress or turbulent kinetic energy is revealed in the wall jet region. The computed results show some deviation from experimental data in the impingement region, where streamline curvature is significant. However, the computed results agree qualitatively well with measurements.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.2 no.3
• /
• pp.10-19
• /
• 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
• /
• 1998.10a
• /
• pp.6-6
• /
• 1998

항공기용 가스터빈 및 일반적인 산업용 분무시스템에서는 많은 양의 분사액체를 미립화 시키고 시스템의 연속적인 운전과 유지를 편리하게 하기 위하여 여러 개의 분사노즐을 열로 설치하여 동시에 분사하도록 하고 있다. 이렇게 동시에 분사할 경우, 노즐간에 거리가 충분히 크지 않으면 개별적으로 분사된 분무들이 서로 합해져서 하나의 연합된 분무군이 형성된다. 이렇게 Two element에 의해서 형성된 spray는 공급압력이 증가함에 따라 관성력이 증가하게 되어 중심부분에서 액막 혹은 액적상태로서 충돌이 발생하여 복잡한 분무특성을 가질 것이다. 따라서, 연합된 분무군의 특성을 이해하는 것은 응용의 측면에서 매우 중요하다고 할 수 있다.

• 한국가시화정보학회:학술대회논문집
• /
• 2004.11a
• /
• pp.10-13
• /
• 2004

The PSP(pressure sensitive paint) technique has recently received a large attention as a new revolutionary optical method to measure absolute pressure distribution on a model surface. The PSP technique can be applied to quantitatively investigate flow structure using a CCD camera and image processing technique. In the static calibration, the luminescent intensity of PSP coatings was measured from 0kPa to 11kPa with 0.5, 1, 2kPa increments. In this study, the low-pressure PSP technique was applied to an oblique impinging jet to measure pressure field variations on the impingement plate with varying angle of an oblique jet. The flow structure over the impingement plate was visualized using a surface tracing method. As a result, the detail pressure field distributions of the oblique low-speed impinging jet were visualized effectively using the PSP technique.

• Journal of Power System Engineering
• /
• v.11 no.4
• /
• pp.26-31
• /
• 2007

Recently, study on the improvement of combustion performance for the diesel engine by using the impinging spray in the combustion chamber has been actively studied. The purpose of this study is to examine the variation of exhaust emission between the trial engine with impinging plate and the prototype engine in accordance with change of fuel injection timing and fuel injection pressure. The concentration of nitrogen oxide of trial engine decreased more than 50% compared to prototype engine. However, smoke of trial engine indicated very high concentration compared to prototype engine. The effect of fuel injection timing on the nitrogen oxide and smoke indicated different results, that is, the concentration of nitrogen oxide decreased as the degree of fuel injection start become slower, whereas the concentration of smoke decreased as the degree of fuel injection start become faster.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.3
• /
• pp.95-105
• /
• 1997

A diesel engine has become smaller and higher, thus sprays injected in high speed may be impinged on a small combustion chamber wall if there is not enough strong swirl. Those combustion chambers should have proper measures to avoid the spray impinged and deposited on a wall. One of the measures is a chamber prepared impingement parts raised on a chamber wall surface. In this system a spray is injected into the raised pip, broken into a number of smaller drops and spreaded out away from the wall surface. Therefore the fuel droplets distributes over inside of the combustion chamber. In this study, the positions, sizes and angles of the raised land are discussed to help the chamber design using spray wall impaction. The characteristics of the spray impinged on various lands are investigated and compared with each other. Then chamber shapes are discussed with the spray characteristics and the proper positions and size are proposed in some chamber volumes.

• The KSFM Journal of Fluid Machinery
• /
• v.12 no.2
• /
• pp.24-30
• /
• 2009

Flow and noise analyses are conducted for examining a new design concept of impinging jet electronics cooling, and the analysis results are compared with conventional electronics cooling techniques. For the application of impinging jet electronics cooling method, the present study considers the air duct where air is supplied by axial fan and air flow from the duct is impinged vertically onto the electronic component heat source. Applying CFD simulation technique and fan noise model to the present cooling scheme, the cooling performance of the impinging jet as well as the operation condition and the noise characteristics of fan are investigated for various impinging jet nozzle conditions and fan models. Furthermore, the impinging jet electronics cooling analysis results are compared with the conventional parallel-flow cooling scheme to give the design concept and criteria of impinging jet cooling method.

• Journal of the Korea Concrete Institute
• /
• v.25 no.5
• /
• pp.485-496
• /
• 2013

In recent years, frequent terror or military attacks by explosion or impact accidents have occurred. Examplary case of these attacks were World Trade Center collapse and US Department of Defense Pentagon attack on Sept. 11 of 2001. These attacks of the civil infrastructure have induced numerous casualties and property damage, which raised public concerns and anxiety of potential terrorist attacks. However, a existing design procedure for civil infrastructures do not consider a protective design for extreme loading scenario. Also, the extreme loading researches of prestressed concrete (PSC) member, which widely used for nuclear containment vessel, gas tank, bridges, and tunnel, are insufficient due to experimental limitations of loading characteristics. To protect concrete structures against extreme loading such as explosion and impact with high strain rate, understanding of the effect, characteristic, and propagation mechanism of extreme loadings on structures is needed. Therefore, in this paper, to evaluate the impact resistance capacity and its protective performance of bi-directional unbonded prestressed concrete member, impact tests were carried out on $1400mm{\times}1000mm{\times}300mm$ for reinforced concrete (RC), prestressed concrete without rebar (PS), prestressed concrete with rebar (PSR, general PSC) specimens. According to test site conditions, impact tests were performed with 14 kN impactor with drop height of 10 m, 5 m, 4 m for preliminary tests and 3.5 m for main tests. Also, in this study, the procedure, layout, and measurement system of impact tests were established. The impact resistance capacity was measured using crack patterns, damage rates, measuring value such as displacement, acceleration, and residual structural strength. The results can be used as basic research references for related research areas, which include protective design and impact numerical simulation under impact loading.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.148-148
• /
• 2013

스퍼터 이온펌프(Sputter Ion Pump)는 주로 화학흡착으로 동작하며 기계적 진동이 없고, 기름 등의 오염 물질을 배출하지 않으며, 수명이 길어 초고청정 진공이 요구되는 표면실험장치, 표면분석계, 입자가속기 등에서 널리 사용 되고 있다. 일정한 지름을 갖는 다수의 원통 양극과 그 양단에 두개의 음극판을 배치시킨 후, 양극과 음극 사이에 수 kV의 전압을 걸고 원통의 축방향으로 자장을 인가하면 페닝 방전이 발생한다. 냉음극에서 방출된 전자는 양극으로 비행하면서 가스를 이온화한다. 이온분자는 가스흡수성 게터재료로 된 음극에 충돌하여 스퍼터링을 일으키며 게터막를 주변에 증착시킨다. 이온 및 중성 가스는 게터 고체막 속에 주입 포획되는 형태로 배기된다. 스퍼터 이온펌프는 $10^{-5}$ Pa 부근에서 최대 배기속도를 가지며, 압력이 낮아질 수록, 특히 $10^{-10}$ Pa영역 이하에서는 그 배기속도가 급격히 저하되며, $10^{-10}$ Pa영역에서는 배기능력을 거의 상실한다. 따라서 스퍼터 이온펌프 단독으로 진공시스템을 배기할 때 도달압력은 $10^{-9}$ Pa 영역에 머무르게 되며, $10^{-10}$ Pa 이하의 극고진공을 얻기 위해서는, $10^{-8}$ Pa 이하의 압력에서 배기 속도가 압력과 무관한 흡착펌프(getter pump)와 이온펌프를 조합하여 사용한다. 본 실험에서는 $600^{\circ}C$ 이상의 온도로 진공로에서 탈개스시킨 진공용기를 배기속도 450, 60, 30, 20, 5, 3 l/s의 6종류의 이온펌프와 배기속도 400 l/s, 100 l/s의 non-evaporable getter (NEG) 펌프를 조합시켜 배기하여 그 배기 특성을 비교하였다. 도달 압력은 이온펌프의 배기속도가 클수록 낮아지는 경향을 보여주었다. 450 l/s 이온펌프와 400 l/s NEG를 조합하여 배기시킬 때 도달 압력은 ~$2{\times}10^{-10}$ Pa을 기록하여 가장 낮았으며, 3 l/s 이온펌프와 400 l/s NEG를 조합하였을 때는 $ 2{\sim}3{\times}10^{-8}$ Pa을 기록하였다. 450 l/s 이온펌프와 400 l/s NEG를 조합한 경우 잔류가스의 대부분이 수소였으나, 3 l/s 이온펌프와 400 l/s NEG의 조합한 경우에는 메탄의 잔류량이 수소 보다 많았다. 이 결과는 메탄을 배기하지 못하는 NEG의 배기 특성을 보완하기 위해서는 일정 배기속도 이상의 이온 펌프가 필요함을 보여준다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.50 no.11
• /
• pp.783-789
• /
• 2022

In a recent study, it was observed that the combustion gas entering the post chamber of a hybrid rocket contains vortices with very small size and high frequency characteristics. In addition, it was observed that small vortices collided with the nozzle wall to create a counter-flow, resulting in additional combustion with ignition delay. This study investigated the physical relationship between ignition delay induced by the counter-flow and the formation of beating pressure. To do this, a newly modified model was proposed by including ignition delay in the existing energy kicked oscillator model proposed by Culick. Numerical results show that the ignition delay is an important factor in determining the occurrence of the combustion pressure beats through the periodic formation of thermoacoustic coupling. In addition, when the ignition delay was reduced by increasing the post chamber length, the phase difference between the energy kick and the pressure generation was increased, the periodic pressure beats did not occur at all.