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Numerical analysis of supersonic jet flow and dust transport induced by air ingress in a fusion reactor

Nuclear Science and Techniques 2021年第7期32卷 72-82页

作者： Bu-Er Wang Shi-Chao Zhang Zhen Wang Jiang-Tao Jia Zhi-Bin Chen Institute of Nuclear Energy Safety Technology Hefei Institutes of Physical ScienceChinese Academy of SciencesHefei 230031China University of Science and Technology of China Hefei 230026China

During a loss of vacuum accident(LOVA),the air ingress into a vacuum vessel(VV)may lead to radioactive dust resuspension,migration,and even explosion,thereby posing a great threat to the safe operation of future fusion reactors;thus,it is crucial to understand the flow characteristics and radioactive dust transport behavior induced by LOVA.However,only a few studies have identified the characteristics of the highly under-expanded jet flow at a scale of milliseconds during LOVA.Particularly,the occurrence and behavior of a Mach disk is yet to be captured in existing studies.In this study,we used a more advanced model with a finer mesh and adaptive mesh strategies to capture the Mach disk in a VV during LOVA.In detail,a computational fluid dynamics–discrete phase model one-way coupled multiphase approach was established using the computational fluid dynamics code ANSYS FLUENT and applied to the analysis during the first seconds of LOVA.The results showed that air ingress into the VV behaved like a highly free under-expanded jet at the initial stage and Mach disk was formed at~6 ms.Moreover,the flow field dramatically changed at the position of the Mach disk.The jet core before the Mach disk had a maximum velocity of~8 Mach with the corresponding lowest static pressure(~100 Pa)and temperature(few tens of K).The friction velocities in the lower part of the VV,which is an area of concern due to dust deposition,were generally larger than 15 m/s near the inlet region.Lastly,the crude prediction of the particle trajectories demonstrated the spiral trajectories of the dust following the air motion.Therefore,this study provided a basis for further safety analysis and accident prevention related to dust transport and explosion in future fusion reactors.

关键词： supersonic jet Radioactive dust Loss of vacuum accident Mach disk Friction velocity

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Experimental investigations on cavity-actuated under-expanded supersonic oscillating jet

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Chinese Journal of Aeronautics 2015年第5期28卷 1372-1380页

作者： Sun Bo Luo Xiaochen Feng Feng Wu Xiaosong Department of Aerospace Engineering Nanjing University of Science and Technology

As one type of potential flow control actuators, cavity-actuated supersonic jet oscillators, which consist of a 2-D convergent nozzle and two face to face cavities, need to be investigated dee- ply to get the knowledge of their oscillating feature and underlying mechanism. Wind tunnel testing are conducted under different back pressures in a vacuum-type wind tunnel for two supersonic jet oscillators, to obtain their characteristics and the conditions for jet oscillating. The experimental results show that the continuous, nearly symmetric or asymmetric flipping between the two cavities appears over certain nozzle pressure ratio （NPR） range for both oscillators according to schlieren visualizations. Compared to the free jet, the oscillating jet with large exit achieves larger mixing; the oscillating jet with small exit has less mixing, based on the analysis of jet axial peak velocity and the entrainment. The cross-junction mode for estimating the resonance frequency in a pipe with two closed side branches is modified and obtained comparable estimations of the frequency of jet flipping with experimental data, but further investigations are needed to discover the underlying mechanism for the jet flipping.

关键词： jet cavity interactions jet flipping Oscillating jet supersonic jet Wind-tunnel testing

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Evolution of wall flow structure and measurement of shear stress issuing from supersonic jet with extended shelf

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Chinese Journal of Aeronautics 2021年第11期34卷 94-105页

作者： Yun JIAO Chengpeng WANG Jiaqi XIE Kang LI Kerning CHENG College of Aerospace Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China Key Laboratory of Unsteady Aerodynamics and Flow Control Ministry of Industry and Information TechnologyNanjing University of Aeronautics and AstronauticsNanjing 210016China

This paper reports an experimental study on the supersonic jet surface flow structure visualization and shear stress field measurement issuing from a rectangular nozzle with extended shelf. The evolution of the near-field surface flow structures with an increased Nozzle Pressure Ratio(NPR) is successfully captured by the surface oil flow, infrared detection technology, and the Shear-Sensitive Liquid Crystal Coating(SSLCC) technique. Results reveal that under smaller NPR, the wall flow structure is similar to that of a jet without the extended shelf i.e., clean jets,and this is caused by insufficient effect on the boundary layer. However, at higher amplitudes of NPR, there exists a significant effect of the boundary layer, as a near triangular separation forms on the trailing edge of the Mach stem due to the adverse pressure gradient, which is visualized for the very first time in this paper. Furthermore, the vector field of shear stress is measured quantitatively by SSLCC technique. Results shows that the magnitude of shear stress heightened with NPR increasing, and the directions of shear stress changes across the shock wave and expansion fans. In addition, surface streamlines measured by SSLCC is significantly consistent with the streamlines visualized using the oil flow technique.

关键词： Evolution of shock structure Flow visualization Quantitative measurement Shear stress supersonic jet

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Experimental investigation on a cavity-step-actuated supersonic oscillating jet

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Chinese Journal of Aeronautics 2017年第1期30卷 274-281页

作者： Luo Xiaochen Sun Bo Wang Xiang'ang Department of Aerospace Engineering Nanjing University of Science and Technology

Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tunnel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rectangular cavity and a backward step, to obtain its characteristics and the conditions for jet oscillating. The experimental results show that periodic asymmetrical flipping of the supersonic jet appears over certain nozzle pressure ratio（NPR） range according to schlieren visualization and pressure fluctuations. The jet flipping appears only when the jet is over expanded. The normalized average amplitude of the lateral pressure difference acting on the roofs of the cavity and the step varies around 0.2 while the periodic flipping appears. The supersonic jet periodic flipping frequencies obtained from the experiments agree well with those from the modified Rossiter mode for cavity-step acoustic resonance, but further investigations are needed to discover the underlying mechanism for the jet flipping.

关键词： jet cavity interactions jet flipping Oscillating jet supersonic jet Wind runnel testing

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Visual analytics of combustion on time-varying turbulent-flow

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Advances in Aerodynamics 2022年第1期4卷 176-187页

作者： Xiaoyang Han Yifei An Guihua Shan Jun Liu Bo Yang Computer Network Information Center Chinese Academy of SciencesBeijingChina University of Chinese Academy of Sciences BeijingChina

Visualization is crucial for analyzing the turbulent combustion simulation.Time-varying data allows us to investigate the evolution process of the turbulent flow field.To study the combustion effects,we calculated the enstrophy of the flow field since high enstrophy region can display valuable features,and extract components based on these features.We isolated large components to track their behaviors and characterized them using volume and spatial locations,which helps scientists to explore the dynamics and temporal changes of intense events individually.We analyzed the components’structures and visualized them in contouring and statistical charts.

关键词： Turbulent combustion supersonic jet Turbulent-flow visualization

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Studies on the Aero-optical Phenomena of Free-vortex Aerodynamic Window′s jet

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Chinese Journal of Lasers 2002年第6期11卷 26-32页

作者：刘天华姜宗福李文煜王云萍刘泽金赵伊君 Beijing 100094 Beijing Institute of Telecommunications and Tracking China National University of Defense and Technology National University of Defense and Technology Changsha 410073 School of Science

The concept of the free vortex aerodynamic windows(FADW) is one of the best effective methods taking the place of the conventional beam output crystal windows of high power laser. An experimental model of the supersonic free vortex aerodynamic window has been designed and made in our latest study. This paper studies the aero optical phenomena of the FADW′s supersonic jet to study the laser optical quality degradation caused by the free vortex jet, and to find out the relation of output laser beam quality through the FADW to the structure of the FADW′s supersonic jet. First it studies the beam quality using the methods of far field beam profile measurement and lateral shearing interferometry, and then it uses the principle of matrix optics interpreting the large scale phase distortion in detail. At last the structure of FADW′s jet has been studied by means of shadowgraphy.

关键词： high power laser free vortex aerodynamic window aero optical phenomena beam quality lateral shearing interferometry far field beam profile measurement shadowgraphy supersonic jet

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