المؤلفون: Liu, Yige, Zhao, Bidan, Xu, Ji, Wang, Junwu

مصطلحات موضوعية: Physics - Fluid Dynamics

الوصف: In order to resolve the pressure checkerboard field problem with collocated grid, it is essential to employ the momentum interpolation method when formulating the pressure equation, and the flux reconstruction method when updating the cell-centered velocity fields. In this study, we first derive a momentum interpolation method for Euler-Euler simulation of gas-solid flows, which is independent of the time step, the transient term discretization scheme, the under-relaxation factor and the shape of grid; a complete first-order flux reconstruction method is then proposed to update the cell-centered velocities. Their effectiveness are proved by simulating the hydrodynamics of solids settlement, gas-solid fixed bed, bubbling fluidized bed and circulating fluidized bed riser, and then comparing the simulation results to the theoretically known solutions. Their superiority over the standard solver of OpenFOAM in suppressing the high-frequency oscillations and enhancing the smoothness and accuracy is also proved. Finally, the difficulty in fully eliminating the high-frequency oscillations is attributed to the insufficiency of current methods in handling the situations where the independent variables undergo abrupt change.

URL الوصول: http://arxiv.org/abs/2405.20629

المؤلفون: Liu, Yige, He, Mingming, Chen, Jianhua, Li, Wen, Zhao, Bidan, Xu, Ji, Wang, Junwu

مصطلحات موضوعية: Physics - Fluid Dynamics

الوصف: Numerical solution of Euler-Euler model using different in-house, open source and commercial software can generate significantly different results, even when the governing equations and the initial and boundary conditions are exactly same. Unfortunately, the underlying reasons have not been identified yet. In this article, three methods for calculating the granular pressure gradient term are presented for two-fluid model of gas-solid flows and implemented implicitly or explicitly into the solver in OpenFOAM: Method I assumes that the granular pressure gradient is equal to the elastic modulus plus the solid concentration gradient; Method II directly calculates the gradient using a difference scheme; Method III, which is proposed in this work, calculates the gradient as the sum of two partial derivatives: one related to the solid volume fraction and the other related to the granular energy. Obviously, only Methods II and III are consistent with kinetic theory of granular flow. It was found that the difference between all methods is small for bubbling fluidization. While for circulating fluidization, both methods II and III are capable of capturing non-uniform structures and producing superior results over Method I. The contradictory conclusions made from the simulation of different fluidization regimes is due to the different contribution of the term related to the granular energy gradient. Present study concludes that the implementation method of granular pressure gradient may have a significant impact on hydrodynamics and is probably a key factor contributing to the observed differences between different simulation software.

URL الوصول: http://arxiv.org/abs/2405.20621

المؤلفون: Zhao, Bidan, Shi, Kun, He, Mingming, Wang, Junwu

مصطلحات موضوعية: Physics - Fluid Dynamics

الوصف: Polydisperse gas-solid flows, which is notoriously difficult to model due to the complex gas-particle and particle-particle interactions, are widely encountered in industry. In this article, a refined kinetic theory for polydisperse flow is developed, which features single-parameter Chapman-Enskog expansion (the Knudsen number) and exact calculation of the integrations related to pair distribution function of particle velocity without any mathematical approximations. The Navier-Stokes order constitutive relations for multifluid modeling of polydisperse gas-solid flow are then obtained analytically, including the solid stress tensor, the solid-solid drag force, the granular heat flux and the energy dissipation rate. Finally, the model is preliminarily validated by comparing to the discrete element simulation data of one-dimensional granular shear flow and by showing that the hydrodynamic characteristics of gas-solid flows in a bubbling fluidized bed containing bidisperse particles can be successfully predicted.

URL الوصول: http://arxiv.org/abs/2311.09495

المؤلفون: Lan, Bin, Xu, Ji, Lu, Shuai, Liu, Yige, Xu, Fan, Zhao, Bidan, Zou, Zheng, Zhai, Ming, Wang, Junwu

مصطلحات موضوعية: Physics - Fluid Dynamics

الوصف: Hydrogen metallurgy technology uses hydrogen as the reducing agent instead of carbon reduction, which is one of the important ways to reduce carbon dioxide emissions and ensure the green and sustainable development of iron and steel industry. Due to the advantages of high gas-solid contact efficiency and outstanding mass and heat transfer, direct reduction of iron ore in fluidized beds has attracted much attention. In this study, a coarse-grained CFD-DEM-IBM solver based on hybrid CPU-GPU computing is developed to simulate the direct reduction process of two kinds of iron ore with hydrogen in fluidized beds, where an unreacted shrinking core model based on multiple reaction paths is used to model the reduction reactions, a coarse-grained model and multiple GPUs enable the significant acceleration of particle computation, and the immersed boundary method (IBM) enables the use of simple mesh even in complex geometries of reactors. The predicted results of particle reduction degree are in good agreement with the experimental values, which proves the correctness of the CFD-DEM-IBM solver. In addition, the effects of reaction kinetic parameters and operating temperature on particle reduction degree are also investigated. Present study provides a method for digital design, optimization and scale-up of ironmaking reactors.

URL الوصول: http://arxiv.org/abs/2311.03908

المؤلفون: Li, Dandan, Zhao, Bidan, Lu, Shuai, Wang, Junwu

مصطلحات موضوعية: Physics - Fluid Dynamics

الوصف: Integration of physics principles with data-driven methods has attracted great attention in recent few years. In this study, a physics-informed dynamic mode decomposition (piDMD) method, where the mass conservation law is integrated with a purely data-driven DMD method, is developed for fast prediction of the spatiotemporal dynamics of solid volume fraction distribution in bubbling fluidized beds. Assessment of the prediction ability using both piDMD and DMD is performed using the CFD-DEM results as the benchmark: Both DMD and piDMD can predict the short-term behaviour of solid volume fraction reasonably well, but piDMD outperforms the DMD in both qualitative and quantitative comparisons; With respect to their long-term ability, the piDMD-based prediction of the instantaneous solid volume fraction distributions is qualitatively correct although the accuracy needs to be improved, and the predicted time-averaged radial and axial profiles are satisfactory; Whereas the DMD-based prediction of instantaneous snapshots and time-averaged results is completely nonphysical. Present study provides a fast and relatively accurate method for predicting the hydrodynamics of gas-solid flows.

URL الوصول: http://arxiv.org/abs/2311.02600

المؤلفون: Hao, Zhuowen, Wang, Ying, Wang, Linlong, Feng, Qinyu, Li, Hanke, Chen, Tianhong, Chen, Jiayao, Wang, Junwu, Shi, Guang, Chen, Renxin, Li, Beihai, Zhou, Shuanhu^{Aff3, IDs10067024069856_cor12}, Jin, Wei^{Aff1, IDs10067024069856_cor13}, Li, Jingfeng^{Aff1, IDs10067024069856_cor14}

المصدر: Clinical Rheumatology: Journal of the International League of Associations for Rheumatology. 43(6):2061-2077

المؤلفون: Zhao, Yunfei^{Aff1, Aff2}, Wang, Xia^{Aff1, IDs00374024018349_cor2}, Li, Yazhen, Yuan, Menghan, Li, Jia, Zhu, Huawei, Cheng, Zhuoyun, Duan, Wenhui, Wang, Junwu

المصدر: Biology and Fertility of Soils. :1-14

المؤلفون: Guo, Feng, Wang, Junwu, Song, Yinghui^{Aff2, IDs11356024331691_cor3}

المصدر: Environmental Science and Pollution Research. 31(23):34507-34525

المؤلفون: Xu, Fan, Su, Jinghong, Lan, Bin, Zhao, Peng, He, Yurong, Sun, Chao, Wang, Junwu

مصطلحات موضوعية: Physics - Fluid Dynamics

الوصف: Direct numerical simulations are performed to explore the effects of rotating direction of the vertical asymmetric rough wall on the transport properties of Taylor-Couette (TC) flow up to a Taylor number of $\textit{Ta} = 2.39 \times 10^7$. It is shown that compared to the smooth wall, the rough wall with vertical asymmetric strips can enhance the dimensionless torque \textit{Nu}$_\omega$, and more importantly, at high \textit{Ta} clockwise rotation of the inner rough wall (the fluid is sheared by the steeper slope side of the strips) results in a significantly bigger torque enhancement as compared to the counter-clockwise rotation (the fluid is sheared by the smaller slope side of the strips) due to the larger convective contribution to the angular velocity flux, although the rotating direction has a negligible effect on the torque at low \textit{Ta}. The larger torque enhancement caused by the clockwise rotation of vertical asymmetric rough wall at high \textit{Ta} is then explained by the stronger coupling between the rough wall and the bulk due to the larger biased azimuthal velocity towards the rough wall at the mid-gap of TC system, the increased intensity of turbulence manifesting by larger Reynolds stress and thinner boundary layer, and the more significant contribution of the pressure force on the surface of rough wall to the torque.
Comment: 17 pages,11 figures

URL الوصول: http://arxiv.org/abs/2310.11642

المؤلفون: Su, Jinghong, Yi, Lei, Zhao, Bidan, Wang, Cheng, Xu, Fan, Wang, Junwu, Sun, Chao

مصطلحات موضوعية: Physics - Fluid Dynamics

الوصف: The presence of a dispersed phase can significantly modulate the drag in turbulent systems. We derived a conserved quantity that characterizes the radial transport of azimuthal momentum in the fluid-fluid two-phase Taylor-Couette turbulence. This quantity consists of contributions from advection, diffusion, and two-phase interface, which are closely related to density, viscosity, and interfacial tension, respectively. We found that the presence of the two-phase interface consistently produces a positive contribution to the momentum transport and leads to drag enhancement, while decreasing the density and viscosity ratios of the dispersed phase to the continuous phase reduces the contribution of local advection and diffusion terms to the momentum transport, respectively, resulting in drag reduction. Therefore, we concluded that the decreased density ratio and the decreased viscosity ratio work together to compete with the presence of two-phase interface for achieving drag modulation in fluid-fluid two-phase turbulence.

URL الوصول: http://arxiv.org/abs/2310.08098