충돌제트에서의 횡방향 유동 감소를 위한 파형 구조의 유동 및 열전달에 관한 연구

황병조(Byeong Jo Hwang),김선호(Seon Ho Kim),주원구(Won Gu Joo),조형희(Hyung Hee Cho) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.5

충돌제트는 제트가 충돌하는 정체 영역에 매우 높은 열전달을 제공하기 때문에 다양한 분야에서 적용되고 있다. 그러나 제트가 벽면에 부딪친 후 벽면 제트에 의해 야기되는 충돌 챔버 내의 횡방향 유동은 여러 개의 제트로 구성된 배열제트인 경우 하류에 있는 제트 유동을 방해하거나 휘게 할 수 있으며, 이로 인해 배열 충돌제트의 냉각 성능은 감소하게 된다. 파형 구조는 하류 제트에서의 횡방향 유동영향을 줄이기 위해 인접한 충돌 제트 사이에 있는 파형 속에 사용된 냉각 공기를 유입시키는 역할을 하며, 이러한 파형 구조에서의 유동 및 열전달 특성에 대해 수치해석을 수행하였다. 3차원, 정상상태, 비압축성 유동으로 고려하고 해석하였으며 ANSYS-CFX 15.0 코드를 사용하였다. 파형 구조의 형상 변수가 배열 충돌제트의 횡방향 유동 억제에 미치는 영향을 제시하고 분석하였다. Impingement jets have been applied in a wide variety of fields as they provide significantly high heat transfer on the impingement-jet stagnation zone. However, the crossflow in an impingement chamber developed by spent wall jets can disrupt and deflect the downstream jets in the array, leading to a decrease in the cooling performance of an array of impingement jets. A numerical analysis is made of the fluid flow and heat transfer characteristics in a corrugated structure that traps the spent air in the corrugations between impingement jets and reduces crossflow effects on downstream jets. All computations are performed by considering a three-dimensional, steady, and incompressible flow by using the ANSYS-CFX 15.0 code. The effects of the configuration parameters of the corrugated structure on crossflow reduction of the array of impingement jets are presented and discussed.

전산유체역학 기반의 고에너지배관 파단 시 초음속 증기제트의 충돌하중 평가 방법론 개발 및 특성 평가

오세홍,최대경,박원만,최청렬,김원태,장윤석 대한기계학회 2019 大韓機械學會論文集B Vol.43 No.5

Recently, the U.S. Nuclear Regulatory Commission indicated the non-conservativeness of ANSI/ANS 58.2, which is a technical standard for evaluating the jet impingement load owing to the high-energy line break accident in a nuclear power plant. Therefore, it is necessary to develop a new methodology that can accurately evaluate the characteristics of jet impingement load caused by a supersonic steam jet. In this study, a numerical analysis methodology for evaluating this load was developed and verified. In addition, the conservativeness of the ANSI jet model was investigated using the developed methodology. The results showed that the ANSI jet model could not sufficiently consider the physical behavior of the under-expanded steam jet and predicted a lower jet impingement load than the numerical analysis results at certain conditions. Thus, it is necessary to improve the jet impingement load evaluation model or introduce a new evaluation technique. 최근 고에너지배관 파단 영향 평가에 사용되는 제트충돌하중 평가 모델의 비보수성 문제가 미국 NRC로부터 제기됨에 따라 초음속 증기제트의 충돌하중 특성을 정확하게 평가할 수 있는 평가 방법론의 개발이 필요한 실정이다. 본 연구에서는 고에너지배관 파단 시 형성되는 부족팽창 제트의 거동 및 충돌하중 특성을 평가하기 위한 수치해석 기법을 수립/검증하였으며, 이를 활용하여 기존의 제트충돌하중 평가 모델(ANSI/ANS 58.2)에 대한 타당성 및 보수성 평가를 수행하였다. 평가결과, 기존의 제트충돌하중 평가 모델은 초음속 제트의 복잡한 물리적 특성을 충분히 고려하지 못함에 따라 비보수적인 평가 결과를 도출할 가능성이 있음을 확인하였고, 제트충돌하중 평가 모델의 개선 또는 신규 평가 기법의 도입이 필요한 것으로 판단된다.

배열충돌제트에서 파형구조 형상 적용에 따른 유동 및 열전달 특성 연구

박철,김선호,손호성,김정주,정의엽,최석민,조형희 대한기계학회 2019 大韓機械學會論文集B Vol.43 No.4

배열 충돌제트는 국소 열전달 성능이 우수하여 가스터빈의 연소기, 베인, 블레이드 등과 같이 높은 냉각성능이 필요한 분야에 적용되고 있다. 하지만 제트가 충돌 후 발생하는 횡방향유동의 영향으로 하류방향으로 갈수록 제트가 편향되어 열전달 성능이 감소하게 된다. 이에 본 연구에서는 제트 홀 사이의 공간을 증가시킨 파형 구조를 이용하여 냉각 성능을 향상시키는 연구를 진행하였다. 제트 홀의 평균 유량은 레이놀드수 10,000이며 ANSYS-CFX 17.2를 사용하여 수치해석을 진행하였다. 변형된 파형구조는 날개 모양의 구조물을 추가로 설치하여 충돌 후 냉각공기가 유입되어 흐를 수 있는 이차유로를 형성함으로써 충돌면에서의 평균 Nusselt 수가 기존 파형구조보다 높게 나타났다. 또한 제트판과 충돌면 사이 간격(h/d)이 클수록 제트의 발달로 인해 정체점에서의 최대 Nusselt 수가 증가하였다. 따라서 제트판과 충돌면 사이의 간격(h/d)이 작을수록 변형된 파형구조의 열전달 성능이 기존 파형구조보다 냉각성능이 높게 나타나는 것을 확인하였다. Array impinging jets have been applied to combustors, vanes and blades of gas turbines that require high cooling performance. However, the jet is deflected toward the downstream direction owing to the influence of the crossflow, which decreases the cooling performance. In this study, a corrugated structure is proposed to increase the space between the jet holes by securing the space for the spent air. The average Reynolds number of each jet hole is 10,000 and numerical simulations are conducted by ANSYS-CFX 17.2. The modified corrugated structure that has an additional plate-making secondary channel for the spent air shows a higher Nusselt number than the corrugated structure. Furthermore, a greater distance of impinging and jet plate (h/d) shows a higher Nusselt number at the stagnation region owing to the development of the jet flow. Therefore, the modified corrugated structure with a smaller distance of impinging and jet plate (h/d) shows greater heat transfer than the corrugated structure.

경사제트에 따른 충돌제트 / 유출냉각에서 열 / 물질전달 특성

홍성국(Sung Kook Hong),이동호(Dong-Ho Rhee),조영희(Hyung Hee Cho) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.4

An experimental investigation was conducted to investigate the heat/mass transfer for impingement/effusion cooling system with inclined jet. Jets with inclined angle of 60 are applied to impingement/effusion cooling. At the jet Reynolds number of 10,000, the experiments were carried out for blowing ratios ranging from 0.0 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result indicates that the inclined jet causes the non-uniform and low heat/mass transfer compared to the vertical jet. At stagnation region, the peak position is shifted from the geometrical center of injection hole due to Coanda effect and its level is higher than that of vertical jet due to increase in turbulence intensity by steep velocity gradient near the stagnation region. Further, the secondary peak region disappears because the interaction between adjacent wall jets weakens. When the initial crossflow occurs, the distorted heat/mass transfer pattern appears. As the blowing ratio (crossflow rate) increases, the heat/mass transfer distributions become similar to those of the vertical jet. This is because the effect of crossflow is dominant compared to that of inclined jet under high blowing ratio (M≥1.0). At low blowing ratio (M≤0.5), averaged Sh value is 10% lower than that of vertical jet, whereas its value at high blowing ratio (M≥1.0) is similar to that of vertical jet.

초음속 증기제트의 충돌하중 특성에 대한 수치해석 연구

오세홍,최대경,박원만,김원태,장윤석,최청렬 한국압력기기공학회 2018 한국압력기기공학회 논문집 Vol.14 No.2

Structures, systems and components of nuclear power plants should be able to maintain safety even in the event of design-basis accidents such as high-energy line breaks. The high-pressure steam jet ejected from the broken pipe may cause damage to the adjacent structures. The ANSI/ANS 58.2 code has been adopted as a technical standard for evaluating the jet impingement load. Recently, the U.S. NRC pointed out the non-conservativeness of the ANSI/ANS 58.2, because it does not take into account the blast wave effect, dynamic behavior of the jet, and oversimplifies the shape and load characteristics of the supersonic steam jet. Therefore, it is necessary to improve the evaluation method for the high-energy line break accident. In order to evaluate the behavior of supersonic steam jet, an appropriate numerical analysis technique considering compressible flow effect is needed. In this study, numerical analysis methodology for evaluating supersonic jet impingement load was developed and verified. In addition, the conservativeness of the ANSI/ANS 58.2 model was investigated using the numerical analysis methodology. It is estimated that the ANSI jet model does not sufficiently reflect the physical behavior of under-expanded supersonic steam jet and evaluates the jet impingement load lower than CFD analysis result at certain positions.

LES 난류모델을 이용한 초음속 증기 충돌제트의 과도하중특성에 대한 수치해석 연구

오세홍,최대경,박원만,김원태,장윤석,최청렬 한국압력기기공학회 2018 한국압력기기공학회 논문집 Vol.14 No.2

In the case of high-energy line breaks in nuclear power plants, supersonic steam jet is formed due to the rapid depressurization. The steam jet can cause impingement load on the adjacent structures, piping systems and components. In order to secure the design integrity of the nuclear power plant, it is necessary to evaluate the load characteristics of the steam jet generated by high-energy pipe rupture. In the design process of nuclear power plant, jet impingement load evaluation was usually performed based on ANSI/ANS 58.2. However, U.S. NRC recently pointed out that ANSI/ANS 58.2 oversimplifies the jet behavior and that some assumptions are non-conservative. In addition, it is recommended that dynamic analysis techniques should be applied to consider transient load characteristics. Therefore, it is necessary to establish an evaluation methodology that can analyze the dynamic load characteristics of steam jet ejected when high energy pipe breaks. This research group has developed and validated the CFD analysis methodology to evaluate the transient behavior of supersonic impinging jet in the previous study. In this study, numerical study on the transient load characteristics of supersonic steam jet impingement was carried out and amplitude and frequency analysis of transient jet load was performed.

차단구조가 적용된 파형 배열충돌제트의 유동 및 열전달 특성

조형희,배성호,김선호,손호성,김태현 대한기계학회 2023 大韓機械學會論文集B Vol.47 No.5

Impingement jet cooling is a method to obtain high heat transfer performance by injecting coolant on the target surface. A cooling method that secures high heat transfer performance over a large area by arranging multiple impingement jets is called an array impingement jet. However, since the coolant injected from the holes arranged in a certain direction impinge with the target surface and exit through the outlet formed downstream, a cross-flow is generated, which results in a degradation of cooling performance. Recently, corrugated structures have been studied to overcome the degradation of heat transfer performance due to cross-flow. In this study, a block-off structure was applied to the corrugated structure for more effective cross-flow reduction. The block-off structure serves to minimize the degradation of heat transfer performance due to cross-flow by forcibly moving coolant to the corrugated structure. The numerical analysis was performed to investigate the flow and heat transfer characteristics of the array impingement jet with the corrugated structure and block-off structure. With the block-off structure, it was confirmed that the thermal performance was improved by about 5% compared to the existing geometry. 충돌제트 냉각은 냉각 대상면에 제트 형태의 냉각 유체를 분사하여 국소적으로 높은 열전달 성능을 얻는 냉각 방식이다. 이러한 충돌제트를 다수 배열하여 넓은 면적에서 높은 열전달 성능을 확보하는 냉각 방식을 배열충돌제트라 한다. 하지만 일정한 방향으로 배열된 충돌제트에서 분사된 냉각 유체들은 냉각 대상면에 충돌 후 하류에 형성되어 있는 출구로 빠져나가려 하기 때문에 횡방향 유동이 생성되고 이는 하류에서 냉각성능이 저하되는 결과를 가져온다. 이를 개선하기 위해 최근 횡방향 유동이 이동할 수 있는 공간을 확보한 파형 배열충돌제트가 연구되고 있다. 본 연구에서는 더욱 효과적인 횡방향 유동의 감소를 위하여 파형 배열충돌제트에 차단 구조를 적용하였고, 이는 냉각 유체가 냉각 대상면에 충격 후 파형구조로 강제로 이동하게 함으로써 횡방향 유동으로 인한 열전달 감소현상을 최소화시키고자 하였다. 수치해석을 통해 차단구조가 적용된 파형 배열충돌제트 형상에 따른 열전달 및 유동 특성을 분석하였고, 차단구조가 설치된 결과에서 기존대비 약 5%가 향상된 열효율이 나타나는 것을 확인하였다.

충돌제트에서의 유량공급 채널 및 제트 홀 배열에 따른 열전달 특성 수치해석

황병조(Byeong Jo Hwang),정희윤(Heeyoon Chung),주원구(Won Gu Joo),조형희(Hyung Hee Cho) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5

충돌제트의 열전달에 유량공급 채널 및 제트 홀 배열이 미치는 영향을 분석하기 위하여 수치해석을 수행하였다. 유량공급 채널 내에 있는 제트 홀은 전연면 채널의 중심축으로부터 일열 또는 엇갈림 배열로 되어 있다. ICEMCFD 소프트웨어를 사용하여 해석영역을 정렬 격자로 모델링하였으며, 수치해석은 CFD 코드인 CFX 15.0으로 수행하였다. 본 해석 결과의 타당성은 타 연구자들의 실험 및 수치해석 결과와의 비교를 통해 검증하였다. 일열 또는 엇갈림 배열인 경우에 충돌 제트의 질량유량 및 충돌면에서의 Nusselt 수 분포에 대해 비교 분석하였다. A numerical analysis is performed to investigate the effect of a supply channel and jet hole arrangement on the heat transfer of impingement jet. The jet holes in a supply channel are composed of an in-line or staggered array from the center of a leading edge channel. The software ICEMCFD is used to generate the structured grids for calculation domain and a CFD code CFX 15.0 to perform the simulation. The present solutions are validated by comparison with the experimental and numerical ones of others. A comparison of mass flow rates of impingement jets and Nusselt numbers on the impingement surface for the in-line or staggered arrays is made.

충돌제트 형태에 따른 유동 특성에 관한 연구

최선아(S.A. Choi),주원구(W.G. Joo) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5

Impinging jet have been used in various industry fields, high temperature surface like turbine blade cooling or various material cleaning. Because flow to inject at the jet exit has an influence the other close jet flow, it changes depending on several parameters. In this research if it has multiple jets, not single jet, it is main purpose to find out how to change the flow characteristics depend on various impinging jets configuration in jet flow. It will be considered parameters such as the number of jets and array of jets, distance between the target plate and jets in this paper. The CFD (computational fluid dynamics) was used to model fluid flow.

평면 충돌제트에서 노즐 깃이 단상 및 비등 열전달에 미치는 영향

신창환(Chang Hwan Shin),임성환(Seong Hwan Yim),우성제(Seong Je Wu),조형희(Hyung Hee Cho) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4

The water jet impingement cooling is one of the techniques to remove heat from high heat flux equipments. We investigate the local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer in the free surface jet and submerged jet. Boiling is initiated from the furthest downstream and the wall temperature increase is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance for H/W≤1 causes the significant increases and distribution changes in heat transfer. Developed boiling reduces the differences in heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to guide plate, H<SUB>c</SUB> are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increase as decreased spacing of collar to heated surface. Heat transfer is enhanced for region from the stagnation to x/W~8 in the free surface jet and to x/W~5 in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet compare with higher velocity condition. It is because the increased velocity by collar is de-accelerated at downstream.