마이크로 초음속 제트유동 특성에 관한 실험적 연구

김종훈(Jong-Hun Kim),방진영(Jin-Young Bang),이열(Yeol Lee) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.8

마이크로 초음속 제트유동 특성에 관한 실험적 연구가 이루어졌다. 노즐 출구직경이 440 ㎛인 음속노즐과 노즐 출구직경이 800 ㎛이고 노즐출구 마하수가 2.0인 Laval 노즐이 파이렉스 관을 이용 제작되어 실험에 사용되었다. 슐리렌 유동가시화와 유동장의 피토압력 분포가 측정되었다. 제트유동의 대표적인 특성인 유동장의 초음속 길이, 제트코어 길이, 속도장의 상사성 및 제트경계의 확산도가 관찰되었다. 실험결과는 보다 높은 레이놀즈수의 초음속 제트유동에 대한 과거 관찰결과와 비교분석 되었으며, 마이크로 제트유동의 전체적인 유동특성은 제트코어 길이와 제트경계 확산특성을 제외하고는 높은 레이놀즈수의 제트유동 특성과 정성적으로 유사함이 확인되었다. An experimental study on the micro-supersonic jet flow fields has been carried out. A sonic nozzle of 440 ㎛-exit diameter and a Laval nozzle of 800 ㎛ exit diameter with the nozzle exit Mach number 2.0 were fabricated by stretching a micro Pyrex glass tube for the present experiments. Schlieren flow visualization and Pitot pressure distribution of the jet flow field were obtained. Representative characteristics of the jet flow fields such as, supersonic length, jet core length, similarity of the velocity field, and jet spreading rates, have been observed. All the results were compared to previous observations of larger supersonic jets of higher Reynolds numbers, and it was found that overall characteristics of the micro supersonic jet are qualitatively similar as those of the higher Reynolds number jets, except the jet core length and the jet spreading rate.

초음속 후향 계단 유동에서 액체 분사로 인한 초음속 제트의 구조 변화

안상훈,한두희,최한영,서성현,성홍계 항공우주시스템공학회 2019 항공우주시스템공학회지 Vol.13 No.6

The experiment on the liquid jet in crossflow in supersonic BFS (backward-facing step) flow was conducted to investigate the mixing characteristics. The working fluids are nitrogen and water. The shadow graph technique was used to visualize the flow field. Images captured by the high-speed camera were applied to analyze the flow phenomena. The liquid jet was injected at the re-circulation zone created by the supersonic jet flow. Experimental conditions are defined based on the pressure of the nitrogen gas chamber and pressurized liquid tank. In respective cases, the penetration depth of liquid jet and location of the Mach disc were observed to be proportional to the momentum ratio of gas and liquid jets. 초음속 유동이 흐르는 후향 계단에서 액체 제트가 수직으로 분사되는 유동의 혼합 특성에 대한 실험적 연구를 수행하였다. 작동 유체는 질소와 물을 사용하였다. 쉐도우그래프 기법을 사용하여 유동을 가시화하였으며, 초고속 카메라로 촬영된 영상은 시간 평균화 처리를 통해 분석에 사용하였다. 액체 제트의 주입구는 초음속 질소가스 유동에 의해 생성되는 재순환 영역 내부에 위치하며 유동방향에 수직하게 분사된다. 실험 조건은 질소가스 챔버와 액체 가압탱크의 압력에 따라 나누었다. 각 실험 조건에서 분사된 액체 제트의 침투 깊이와 마하 디스크의 생성 위치의 변화를 관찰하였으며, 운동량비에 따른 유동의 구조 변화에 대해 고찰하였다.

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.

CFD를 이용한 고압파이프 파단 시 초음속제트의 압축성유동 특성에 관한 수치해석

정종길(Jong-Kil Jung),김광추(Kwang-Chu Kim),윤준규(Jun-Kyu Yoon) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.10

고압의 파이프 파단 시 파이프 내에 있던 유체가 고속으로 대기로 분출될 때 압축성유동을 동반하는 초음속제트가 발생한다. 이러한 초음속제트는 일반적으로 복잡한 비정상거동을 보여줄 수 있다. 본 연구는 이러한 고압파이프에서 분출되는 초음속제트에 의해 생성되는 압축성유동을 고찰하기 위하여 전산유체역학 해석이 수행되었다. 분출기체의 종류 및 파이프직경 변화에 따른 비정상유동 특성을 해석하기 위해 SST k - ω 난류모델이 채택되었다. 전산해석 시 기본 경계조건은 파이프직경 10 cm, 제트 압력비 5, 기체온도 300 K로 가정하였다. 그 해석결과로 초음속제트로 인해 생성되는 충격파의 거동이 관찰되었고, 간접적인 영향으로 폭풍파도 발생됨을 알 수 있었다. 기체의 분자량이 가장 작은 H₂의 압력파 특성은 안전영역까지의 거리가 가장 짧았으며, 분자량이 비슷한 N₂, 공기 및 O₂는 큰 차이가 없었다. 또한 파이프직경이 커져 제트에 의한 영향범위도 더욱 증대됨을 알 수 있었다. A rupture in a high-pressure pipe causes the fluid in the pipe to be discharged in the atmosphere at a high speed resulting in a supersonic jet that generates the compressible flow. This supersonic jet may display complicated and unsteady behavior in general . In this study, Computational Fluid Dynamics (CFD) analysis was performed to investigate the compressible flow generated by a supersonic jet ejected from a high-pressure pipe. A Shear Stress Transport (SST) turbulence model was selected to analyze the unsteady nature of the flow, which depends upon the various gases as well as the diameter of the pipe. In the CFD analysis, the basic boundary conditions were assumed to be as follows: pipe of diameter 10 cm, jet pressure ratio of 5, and an inlet gas temperature of 300 K. During the analysis, the behavior of the shockwave generated by a supersonic jet was observed and it was found that the blast wave was generated indirectly. The pressure wave characteristics of hydrogen gas, which possesses the smallest molecular mass, showed the shortest distance to the safety zone. There were no significant difference observed for nitrogen gas, air, and oxygen gas, which have similar molecular mass. In addition, an increase in the diameter of the pipe resulted in the ejected impact caused by the increased flow rate to become larger and the zone of jet influence to extend further.

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.

Effect of Mesh Screen Device on Over-Expanded Supersonic Jet Noise

Yong-Hun Kweon(권용훈),Jae-Hyung Kim(김재형),Chae-Min Lim(임채민),Toshiyuki Aoki(靑木俊之),Heuy-Dong Kim(김희동) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

This paper describes an experimental work to investigate the effect of mesh screen device on the jet structure and acoustic characteristics of over-expanded supersonic jet. The mesh screen device is placed into the supersonic jet stream. In order to perturb mainly the initial jet shear layer, the hole is perforated in the central part of the mesh screen. The diameter of the perforated hole and the location of mesh screen device are varied. A Schlieren optical system is used to visualize the flow fields of supersonic jet without and with the mesh screen device. Pitot pressure measurement is carried out to obtain the pressure distribution in the jet flow. Acoustic measurement also is performed to obtain the OASPL and noise spectra. The results obtained show that the jet structure and the jet noise control effectiveness is strongly dependent upon the diameter of the perforated hole and the location of the mesh screen device in the jet stream. Provided that the mesh screen device is placed at the location to perturb effectively the initial shear layer, the present control method is effective in suppressing the supersonic jet noise.

초음속 제트의 스크리치 톤 주파수 특성에 관한 수치적 연구

김용석,유기완,황창전,이덕주 한국전산유체공학회 2007 한국전산유체공학회지 Vol.12 No.1

An axisymmetric supersonic screeching jet is numerically simulated to examine the length scales of screech frequency as well as screech tone generation mechanism. The axisymmetric Reynolds-averaged Navier-Stokes equations in conjuction with a modified Spalart-Allmaras turbulence model are employed. It is demonstrated that the axisymmetric jet screech tones can be simulated correctly and the numerical results are in good agreement with the experimental data. Instability waves, shock-cell structures and the phenomena of shock motion are investigated in detail to identify the screech tone generation mechanism. Shock spacings and standing wave length are analyzed to determine the dominent length scale crucial to the screech frequency formulation.

다중노즐에서의 초음속 제트 소음에 대한 수치해석

고성호(Sungho Ko),곽영균(Youngkyun Kwack),한승열(Seungyeul Han) 한국유체기계학회 2009 유체기계 연구개발 발표회 논문집 Vol.2009 No.-

Numerical studies were performed to analyze effect of nozzle number on supersonic jet noise. When the nozzle of antitank guided missile(ATGM) exhausts a plume, the supersonic blast wave is created and makes a complicated flux and supersonic jet noise. The method of similarity modelling is used to analyze the supersonic jet noise of multiple nozzle jets as well as a single nozzle jet. Numerical results show that the sound pressure level of multiple nozzle jet is lower than that of a single nozzle jet.

반사판이 초음속 제트 유동장에 미치는 영향에 관한 실험적 연구

권용훈(Yonghun Kweon),임채민(Chaemin Lim),靑木俊之(Toshiyuki Aoki),김희동(Heuydong Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

The present study describes an experimental work to investigate the effect of a reflector on the flow-field of the supersonic jet issuing from a convergent-divergent nozzle. A reflector is placed in the exit of nozzle and its size is varied. A high-quality Schlieren optical system is used to visualize the flow-field of supersonic jet with and without a reflector. Pitot pressure measurement is also carried out to specify the supersonic jet with and without a reflector. The results obtained clearly show that the strength of the supersonic jet oscillation increases as the reflector is installed. It is also found that the placement of a reflector substantially reduces the supersonic length.