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Numerical study on the wake structures of a sphere in linearly stratified flow

JOURNAL OF VISUALIZATION 2025年第1期28卷 97-113页

作者： Shi, Liu Liu Wei, Na Chen, Er Yun Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

In this study, numerical simulations have been carried out to evaluate the influence of internal Froude number (Fr) on the wake characteristics of a sphere in linearly stratified flow. Five models with different levels of Fr (Fr = 0.05, 0.2,0.25,0.5 and 1) at a Reynolds number of Re = 3700 have been selected for comparative study. UDF (User Defined Function) is employed to establish linear density stratification. The influences of stratification on wake characteristics are studied by analyzing the wake patterns, vortical structures, velocity distributions, and lee waves. The results of the study demonstrate that reduced Fr values lead to heightened vertical suppression of the near wake, while increased stratification prompts a transformation of the wake's three-dimensional coherent structures towards quasi-two-dimensionality. Furthermore, the presence of stratification notably impacts the length and amplitude of the lee wave.

关键词： Linearly stratified flow Internal Froude number Wake Lee wave

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Spatio-Temporal flow Field Prediction of Turbulent Boundary Layer Based on PINN

Spatio-Temporal Flow Field Prediction of Turbulent Boundary ...

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Vortex Workshop on New Progress in Vortex Identification and Applications, VW 2023

作者： Zhu, Jiahao Song, Yang Dong, Xiangrui School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer for Power Engineering Shanghai200093 China

ISBN: (纸本)9789819786077

Based on the PINN neural network for the study of turbulence, it can solve the nonlinear equations without grid, which is different from the CFD method. This paper mainly uses the PINN method to study the temporal and spatial prediction of the turbulent boundary layer flow field, and in the absence of label values, based on the known flow field information, the unknown information is reasonably predicted by solving the N-S equation. The comparison of PINN prediction results with numerical simulation and experimental results verifies the feasibility of applying PINN to the study of turbulent boundary layer. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.

关键词： Computational fluid dynamics

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Exploring the mechanisms behind dual-peak formation in energy harvesting efficiency of semi-passive flapping airfoils with varied spring stiffness

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APPLIED MATHEMATICAL MODELLING 2024年 135卷 504-523页

作者： Zhu, Bing Xiao, Qisheng Li, Baiqin Univ Shanghai Sci & Technol Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

Flapping airfoil energy harvesting has emerged as a promising paradigm inspired by birds and marine organisms. In this investigation, a semi-passive flapping airfoil device with a predetermined pitching motion was examined using a transient numerical simulation method employing an overlapping grid technique. The impact of the spring stiffness on the energy harvesting characteristics of the flapping airfoil was analyzed through the implementation of the integral momentum theorem and dynamic mode decomposition. The results demonstrated that the efficiency and power curves of the flapping airfoil exhibited a distinctive bimodal M shape in response to variations of the spring stiffness. The initial peak efficiency point, which corresponded to the system ' s natural frequency in proximity to the pitching frequency, was found to be heavily influenced by the presence of leading-edge vortexes, thereby influencing lift generation. By utilizing the integral momentum theorem, it was determined that the Lamb vector term, fluid acceleration term, and total pressure term predominantly contributed to the lift generation. The emergence of the second peak efficiency point was primarily linked to torque variations induced by trailing-edge vortexes.

关键词： Semi-passive flapping airfoil Integral momentum theorem Dynamic modal decomposition Leading-edge vortex Trailing-edge vortex

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Experimental study on the flow pattern and local heat transfer characteristics of water flow boiling in a vertical upward narrow rectangular channel heated by steam

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APPLIED THERMAL engineering 2024年 247卷

作者： Jin, Cheng Tao, Leren Gu, Shengjie Ju, Yiwei Zhao, Xiefei Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

flow boiling was experimentally investigated in a vertical rectangular narrow channel using water as working fluids. The channel was heated by steam to simulate the heating conditions of plate type rising film evaporators. The geometric dimension of the channel is 1400 mm x 240 mm x 2.75 mm. The experiments were carried out with mass flux in the range of 4.04-12.11 kg/(m2 & sdot;s), inlet temperature in the range of 75-95 degrees C and steam heating power in the range of 2.5-6.0 kW. A data reduction method for local heat transfer under steam heating conditions was established and the parameters for local heat transfer characteristics were calculated. The heat transfer mechanism was revealed with the analysis of the flow pattern maps and local heat transfer characteristics. Different types of flow pattern maps were drawn and compared with other researchers' data under adiabatic and electrical heating conditions. The experimental results showed that the variation trend of the local heat transfer heat flux and coefficient varies under different mass fluxes and inlet temperatures and the optimal point of heat transfer ability appears in the churn-annular flow region. The most suitable heating power under a given working condition can be obtained to maximize the utilization of rectangular narrow channel heat exchangers.

关键词： flow boiling Narrow rectangular channel flow pattern heat transfer

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Evaporation of Non-Isothermal Wall Microlayer Based on the Lattice Boltzmann Method

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PROCESSES 2025年第3期13卷 872-872页

作者： Dang, Mengyuan Gao, Ming Yang, Jianhua Dong, Wuhan Zhang, Lixin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China South China Univ Technol Sch Chem & Chem Engn Key Lab Enhanced Heat Transfer & Energy Conservat Educ Minist Guangzhou 510640 Peoples R China

In the process of boiling heat transfer, the microlayer is not only a crucial medium for enhancing heat transfer but also directly determines the heat flux distribution, dry zone expansion, and overall heat transfer efficiency through its morphological evolution and evaporation behavior. Building on this, this study employs the Lattice Boltzmann Method (LBM) with a single-component multiphase model to numerically simulate the evaporation process of microlayers on non-isothermal walls. The results show that, due to the uneven velocity distribution in the flow field, the microlayer exhibits significant contraction behavior during evaporation, particularly at the three-phase contact point, where velocity differences lead to fluid accumulation and the formation of a "cap-like" structure. The initial growth of the dry zone follows a linear trend, but its growth rate gradually decreases as the microlayer thickness increases, while near-wall density effects result in residual thickness within the dry zone. Additionally, the microlayer height first increases and then decreases over time, accompanied by a noticeable time lag. heat flux analysis reveals that, during the formation of the dry spot, the lowest heat flux occurs at the three-phase contact point, followed by a sudden increase. A cold air ring forms above the dry zone, expanding and splitting as it moves with the dry spot. Higher temperatures promote microlayer evaporation, with the evaporation volume exhibiting nearly linear growth and the total fluid mass decreasing linearly.

关键词： microlayer three-phase contact point heat flux evaporation rate Marangoni effect

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Computational Fluid Dynamics Based Modeling of Gas Absorption Process: A State-of-the-Art Review

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INDUSTRIAL & engineering CHEMISTRY RESEARCH 2024年第18期63卷 7959-8002页

作者： Liu, Dunyu Wang, Zhen Cai, Yuyang Chen, Jun Jin, Jing Zhao, Bingtao Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

The effective removal of gas phase species relies on effective gas liquid hydrodynamic contact coupling with fast chemical reaction rates. To promote mass transfer rate and the development of reagents, computational fluid dynamic modeling has long been recognized as an effective methodology for the quantification of physical and chemical parameters. The simulation of the gas liquid process involves the coupling of models including multiphase flow, turbulence, interfacial forces, mass transfer, and chemical reactions. The selection of suitable models according to practical applications has been challenging. In terms of multiphase flow, volume of fraction, Euler-Euler, and Euler-Lagrange approaches are discussed. With regard to turbulence, direct numerical simulation, large eddy simulation, and Reynolds averaged Navier-Stokes approach are compared. With respect to interfacial forces, the dominance of drag, lift, virtual mass, wall lubrication, and turbulent dispersion forces for different situations are obtained. In terms of mass transfer, the development and applications of film model, dimensionless analysis, penetration model, and surface renewal model are discussed. Different methodologies to enhance mass transfer include improvement of equipment structure, addition of nanofluid, and exposure to an energy field are summarized. To accelerate the computational process, four methods including the space-time conservation element and solution element model, compartmental model, reduction in dimension, and multiscale approach are discussed. This paper intends to provide a thorough review on the applications of different models to different situations and, in particular, to reveal the restrictions of different models. Overall, this study lays the foundation for future studies on the optimization of scrubbers for large scale practical applications. It also allows a deeper understanding of the interactions of fluid dynamics, mass transfer, and chemical reactions.

关键词： Bubbles Gases Liquids Mass transfer Physical absorption

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Temperature distribution measurement of solid propellant combustion based on dual-wavelength imaging method

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MEASUREMENT 2025年 247卷

作者： Yang, Bin Cao, Huayu Li, Lingfeng Fan, Rong Wang, Zhixin Yang, Yang Shi, Zhiquan Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Shanghai Space Prop Technol Res Inst Shanghai 201109 Peoples R China

The combustion temperature is an important parameter that characterizes the combustion behavior and energy of solid propellants. It can provide data support for the research of solid propellant combustion mechanisms and the establishment of combustion models. However, the combustion of solid propellants involves hightemperature and multiphase physical and chemical processes, which pose difficulties for thermometry. Therefore, this study selected the 680 nm and 760 nm wavelengths through mathematical simulation and designed a dual wavelength radiation image measurement system for spectral splitting. The temperature distributions of HTPB propellant with different formulas were obtained using this system. The combustion temperatures of three different formulas of propellants are 2045.3K, 1915.5K, and 1855K, respectively;The uncertainties are +/- 29.8K, +/- 33.9K, and +/- 31.8K, respectively. The measurement results show that aluminum content is an important factor affecting the combustion characteristics of HTPB solid propellants. As the aluminum content increases, the combustion temperature and rate will also increase, and the flame shape will also change accordingly. It provides effective measurement methods for the analysis of combustion performance and formulation optimization of solid propellants.

关键词： Combustion diagnostics Temperature measurement method Solid propellant Dual-wavelength temperature measurement method Radiation imaging method

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Study on characteristics of phase-isolation caused by different classic axial flow swirlers in upward vertical gas-liquid two-phase flow

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EXPERIMENTAL THERMAL AND FLUID SCIENCE 2024年 150卷

作者： Yang, Yang Hu, Haihang Wang, Haoyu Zhang, Chao Yang, Bin Zhao, Huaifen Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

The characteristics of phase-isolation of annular flow caused by axial flow swirler are very critical for separation efficiency of axial inlet separator and accuracy of phase-isolation based measurement method. However, there are lack of comparative study among different types of swirlers and research focusing on characteristics of phaseisolation. In this paper, the phase-isolation characteristics caused by four different classic axial flow swirlers with the same main structural parameters were firstly experimentally studied in upward vertical gas-liquid two-phase flow. Five flow patterns were proposed after obvious evolution in phase distribution at downstream of the swirler, including gas-column flow, swirling annular flow, central bubble flow, central bubble-column flow, and variable diameter gas-column flow. According to the different phase-isolation characteristics, flow patterns downstream of the swirler were divided into stable phase-isolation, quasi-phase-isolation, and non-effective phaseisolation. The corresponding flow pattern maps were also obtained respectively. The experimental results also show that the swirler with good phase-isolation performance generally requires a larger pressure drop as the cost. Finally, the flow in the swirlers was studied numerically. It is found that although the outlet angle of the swirlers is the same, different types of swirlers will result in flow with different deflection angle, and eventually cause the different phase-isolation performance.

关键词： Gas-liquid two-phase flow Phase-isolation Swirler flow pattern

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Heterogeneous Nucleation of Vapor on Insoluble Particles Predicted by an Improved Classical Nucleation Theory

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AEROSOL SCIENCE AND engineering 2024年第2期8卷 133-145页

作者： Yin, Linhao Fan, Fengxian Zhang, Chao Bu, Longxiang Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

The classical nucleation theory (CNT) plays an important role in the investigation of vapor heterogeneous nucleation on solid surfaces. However, the CNT relies on the macroscopic surface tension to describe the formation of a nano-sized embryo, which inevitably causes the model inaccuracy. In this study, an improved CNT is developed by integrating the microscopic surface tension as a function of the embryo size obtained using the molecular dynamics (MD) simulation to enhance the model accuracy. The important heterogeneous nucleation behaviors, including the Gibbs free energy of embryo formation, critical saturation ratio, and nucleation probability, are numerically investigated by the improved CNT. Compared with the CNT with the macroscopic surface tension, the improved CNT using the microscopic surface tension predicts lower Gibbs free energy of embryo formation, lower critical saturation ratio, and higher nucleation probability, particularly when the contact angle of the particle is large. The improved CNT proposed in this study is validated by comparing the numerically predicted critical saturation ratios for the heterogeneous nucleation of water vapor on planar surfaces and on nano- and micron-sized insoluble particles with the experimentally measured data published in literature.

关键词： Vapor heterogeneous nucleation Insoluble particle Classical nucleation theory Molecular dynamics approach Surface tension

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Study of flow pattern transition criterion and heat transfer characteristics in vertical rectangular narrow channel for steam heating

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2024年 220卷

作者： Gu, Shengjie Tao, Leren Jin, Cheng Ju, Yiwei Zhao, Xiefei Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

This study clarifies the heat transfer characteristics of flow boiling in a narrow vertical rectangular channel at each stage and optimizes the performance of a heat exchanger. The flow pattern and local heat transfer characteristics in a narrow vertical rectangular channel of steam heating with dimensions of 1400 x 250 x 2.75 mm (l x w x s) were experimentally investigated using deionized water as the working medium. Based on the visualization data, the mechanical model and empirical formulas in previous literature, a preliminary derivation of the flow pattern transition criterion for steam heating in a vertical rectangular narrow channel was obtained. The effects of the inlet temperature, mass flux, and heating power on the local heat transfer characteristics were analyzed in conjunction with the flow patterns. Based on the parametric analysis of the experimental data, a new flow boiling heat transfer correlation formula was obtained and applied to the experimental conditions. The results showed that an increase in the inlet temperature had a positive effect on the nucleate boiling section, whereas the effect on the local heat transfer coefficient was minimal after entering the churn flow phases. The increase in mass flux decreased the local heat transfer coefficient in the nuclear state boiling stage and enhanced the local heat transfer coefficient in the evaporation zone of the liquid film flow. The peak of the local heat transfer coefficient tended to shift to the left as the heating power increased. The proposed heat transfer correlation equation could well predict the local heat transfer coefficient of flow boiling in a vertical rectangular narrow channel heated by steam under these experimental conditions.

关键词： flow boiling Narrow rectangular channel flow pattern heat transfer

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