流体动力学
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显示 2025年08月06日， 星期三 新的列表
- [1] arXiv:2508.02706 [中文pdf, pdf, 其他]
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标题： 真实飞机构型近场中发动机位置对尾迹云形成和演变的数值研究标题： Numerical investigation of engine position effects on contrail formation and evolution in the near-field of a realistic aircraft configuration主题： 流体动力学 (physics.flu-dyn)
本研究调查了发动机位置对真实三维飞机构型中尾迹云形成和近场演化的影响力。 使用雷诺平均纳维-斯托克斯（RANS）方法并结合网格自适应技术进行了详细的数值模拟。 采用欧拉微物理模型来表征尾迹云冰晶特性及其在不同稀释条件下的演化。 设置基于波音777类似的几何结构，包括机身、机翼、发动机和水平尾翼。 考虑了两种微物理活化情景：一种包含基于吸附的冰核形成，另一种假设完全活化的碳烟颗粒。 后者针对两种碳烟数量排放指数。 稀释过程和尾涡结构对发动机位置表现出强烈的依赖性，这显著影响羽流的饱和度。 在高度稀释的配置中，早期混合增强会降低羽流温度并增加相对湿度，有利于较大冰晶的生长。 根据碳烟数量浓度，蒸汽耗尽效应可能会超过水蒸气可用性的稀释驱动变化。 在吸附限制活化情景中，增加的稀释会降低硫物种浓度，导致活化分数降低并形成较小的冰晶。 此外，在各种情景中，修改后的喷流-涡旋相互作用改变了粒子分布及其对水蒸汽的接触，进一步塑造其生长。 这些效应最终影响尾迹云的光学特性，尤其是其光学厚度。
The present study investigates the impact of engine position on contrail formation and near-field evolution in a realistic three-dimensional aircraft configuration. Detailed numerical simulations are conducted using a Reynolds-Averaged Navier-Stokes (RANS) approach coupled with mesh adaptation techniques. A Eulerian microphysical model is used to characterize contrail ice crystal properties and their evolution under varying dilution conditions. The setup is based on a Boeing 777-like geometry, including fuselage, wings, engines, and tailplane. Two microphysical activation scenarios are considered: one incorporating adsorption-based ice nucleation and the other assuming fully activated soot particles. The latter for two soot number emission indices. The dilution process and wake structure exhibit a strong dependence on engine placement, which significantly influences plume saturation. In highly diluted configurations, enhanced early-stage mixing reduces plume temperature and increases relative humidity, favoring the growth of larger ice crystals. Depending on the soot number concentration, vapor depletion effects may outweigh dilution-driven changes in water vapor availability. In adsorption-limited activation scenarios, increased dilution reduces the concentration of sulfur species, leading to a lower activation fraction and the formation of smaller ice crystals. Additionally, across the scenarios, the modified jet-vortex interaction alters particle distribution and their access to water vapor, further shaping their growth. These effects ultimately impact the contrail's optical properties, particularly its optical thickness.
- [2] arXiv:2508.02727 [中文pdf, pdf, html, 其他]
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标题： 现实大型风电场的功率损耗机制和最佳感应因子标题： Power loss mechanisms and optimal induction factors for realistic large wind farms评论： 正在考虑发表在《Flow》（17页，8图）上主题： 流体动力学 (physics.flu-dyn)
大型风电场中的功率损耗机制由于风电场空气动力学的多尺度特性而变得复杂。 基于双尺度动量理论的最新研究为该领域带来了新的见解；然而，大多数研究都局限于理想化的风电场场景。 为了更好地理解实际风电场的功率性能，在本研究中我们将双尺度动量理论的框架扩展到非理想涡轮机设计和布局场景，然后引入简单的解析子模型来考虑相关的功率损耗。 这些扩展提供了一个全面的观点，说明涡轮机设计、布局、运行条件和大气条件如何共同决定实际风电场中不同类型功率损耗的数量，包括由于涡轮机尾流干扰（即“内部”功率损耗）和风电场与大气相互作用（即“外部”功率损耗）引起的损耗。 我们还提出了一种简单的迭代方法，用于计算在给定条件下（包括边界层高度）最大化整个风电场功率的最佳风电场诱导因子。 类似于叶片元动量理论在风力涡轮机设计优化中起着关键作用，目前的理论预计将在风电场设计优化中发挥关键作用。
Power loss mechanisms in large wind farms are complex due to the multiscale nature of wind farm aerodynamics. Recent studies based on the two-scale momentum theory have brought new insights into this field; however, most of them have been limited to idealised wind farm scenarios. To better understand the power performance of real wind farms, in this study we extend the framework of the two-scale momentum theory to non-ideal turbine design and layout scenarios, and then introduce simple analytical sub-models to account for the associated power losses. These extensions provide a holistic view of how the turbine design, layout, operating conditions and atmospheric conditions collectively determine the amounts of different types of power losses in real wind farms, including the losses due to turbine-wake interference (i.e. `internal' power loss) and farm-atmosphere interaction (i.e. `external' power loss). We also present a simple iterative method for calculating the optimal farm induction factor that maximises the overall farm power for a given set of conditions, including the atmospheric boundary layer height. Analogously to the blade-element momentum theory playing a key role in wind turbine design optimisation, the present theory is expected to play a key role in wind farm design optimisation.
- [3] arXiv:2508.02832 [中文pdf, pdf, 其他]
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标题： 超疏水和润滑剂浸渍表面的水入射动力学：理论与实验视角标题： Water Entry Dynamics of Superhydrophobic and Lubricant-Impregnated Surfaces: A Theoretical and Experimental Perspective主题： 流体动力学 (physics.flu-dyn) ; 软凝聚态物理 (cond-mat.soft)
在当前的研究中，对超疏水和润滑剂浸渍的铝球在液体表面上的撞击动力学进行了全面的研究。 该研究深入探讨了撞击过程中的水动力润滑行为及由此产生的现象。 Worthington射流和空腔提供了对基本力的更深入了解。 实验分析和理论模型表明其在流体动力学、摩擦学和材料科学等多个领域的潜在应用。 对铝纹理球体的稳定性进行了研究，并对射流高度和断裂现象进行了详细分析。 对超疏水表面上的夹带空气以及LIS中的油在获得更高射流方面的实验进行了。 实验装置涉及一个精心设计的装置，通过高速成像技术进行撞击分析。 参数如撞击速度、韦伯数和球体直径被系统地改变，以了解它们对观察到的动力学的影响。 润滑剂的粘度选择使得其与水的粘度相当。 此外，对润滑剂浸渍表面（LIS）的研究评估了与控制表面和纹理表面相比的摩擦损失，即阻力减少。 总之，对撞击动力学的有价值的见解推进了我们对水动力润滑及其应用的理解。 本文提出的发现强调了进一步研究优化表面特性、选择合适的润滑剂以及探索流体动力学、表面工程和机械工程领域更广泛应用的重要性。
In this current work, a comprehensive investigation into the impact dynamics of superhydrophobic and lubricant-impregnated aluminium sphere balls on liquid surfaces were carried out. The study delves into the hydrodynamic lubrication behavior and the resulting phenomena during impact. The Worthington jet and cavity associated give more insight into fundamental forces. The experimental analysis and theoretical modeling suggest potential applications in various fields such as fluid dynamics, tribology, and materials science. The stability investigation on an aluminum-textured sphere ball is carried out, and the evaluation of jet height and pinch-off phenomena is analyzed in detail. The experiment on entrapped air on a superhydrophobic surface and the oil inside the LIS for greater height was performed. The experimental setup involved a carefully designed apparatus for impact analysis by utilizing high-speed imaging techniques. Parameters such as impact velocity, Weber number, and sphere diameter were systematically varied to understand their influence on the observed dynamics. The lubricant viscosity is chosen such that it is comparable to water viscosity. Furthermore, the study on Lubricant Impregnated Surfaces (LIS) assessed frictional losses, i.e., drag reduction, compared to control and textured surfaces. In conclusion, the valuable insights into the impact dynamics advance our understanding of hydrodynamic lubrication and its applications. The findings presented here underscore the importance of further research in optimizing surface properties, selecting suitable lubricants, and exploring broader applications in the fields of fluid dynamics, surface engineering, and mechanical engineering.
- [4] arXiv:2508.03176 [中文pdf, pdf, html, 其他]
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标题： 使用开源软件对 Rushton 涡轮搅拌槽进行 CFD 仿真，并对基于 MRF 的旋转建模进行关键评估标题： CFD simulation of a Rushton turbine stirred-tank using open-source software with critical evaluation of MRF-based rotation modeling期刊参考： 力学 60 (2025) 1613-1637主题： 流体动力学 (physics.flu-dyn)
对多参考系（MRF）技术在稳态RANS模拟搅拌罐中 Rushton 涡轮机影响的批判性评估被提出。 该分析基于开源软件 OpenFOAM，重点在于 MRF 区域的直径和厚度的选择及其对预测速度场和罐内混合时间的影响。 在相同涡轮操作条件下比较了五种不同直径的 MRF 区域，显示速度分布的差异有限，通常与现有实验数据有良好一致性。 然而，在罐内湍流强度的预测水平上发现了显著差异，对于最大直径的 MRF 区域，在 MRF 区域边界处产生了大量人工生成的湍流。 通过使用冻结流动场假设模拟被动标量的释放，评估了不同湍流场预测对罐内混合过程建模的影响。 结果表明，当比较不同尺寸的 MRF 区域时，混合时间的变化可达三倍。 因此，本研究强调了在基于 RANS 的搅拌罐模拟中，将评估 MRF 区域大小对数值结果的影响作为标准做法的重要性。
A critical evaluation of the impact of the Multiple Reference Frame (MRF) technique on steady RANS simulations of a Rushton turbine stirred-tanks is presented. The analysis, based on the open source software OpenFOAM, is focused on the choice of the diameter and thickness of the MRF region and on their effect on the predicted velocity field and mixing times in the tank. Five diameters of the MRF region are compared for the same operating conditions of the turbine, showing limited differences in velocity profiles, which are found in general good agreement with available experimental data. Significant differences are nonetheless found in the predicted levels of turbulence intensity within the tank, with a considerable amount of artificially generated turbulence at the boundary of the MRF region for the largest diameters. The impact of the different predictions of the turbulent field on the modeling of the mixing process in the tank is evaluated by simulating the release of a passive scalar, using the frozen-flow field hypothesis. The results show changes in mixing times up to a factor of three when comparing MRF regions of different size. Thus, the present investigation highlights the importance of assessing the effect of the MRF zone size on numerical results as a standard practice in RANS based simulations of stirred-tanks.
- [5] arXiv:2508.03183 [中文pdf, pdf, html, 其他]
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标题： 矩形柱体时空壁面压力预测的物理感知DeepUFNet标题： Spatiotemporal wall pressure forecast of a rectangular cylinder with physics-aware DeepUFNet评论： 总共26页，21图主题： 流体动力学 (physics.flu-dyn) ; 人工智能 (cs.AI) ; 计算工程、金融与科学 (cs.CE)
壁面压力在理解由流体引起的力和结构响应方面非常重要。 最近的研究已经探讨了深度学习技术在预测平均压力系数和脉动压力系数方面的潜力，但现有的大多数深度学习框架仅限于使用完整的空间信息来预测单个快照。 为了预测矩形圆柱体流动的时空壁面压力，本研究开发了一种物理感知的DeepU-Fourier神经网络（DeepUFNet）深度学习模型。 DeepUFNet结合了UNet结构和傅里叶神经网络，在模型训练阶段嵌入了物理高频损失控制以优化模型性能，其中参数$\beta$随着训练周期的发展而变化。 进行了风洞测试，使用高频压力扫描收集侧比为1.5的二维矩形圆柱体在攻角为零时的壁面压力，从而构建了一个用于DeepUFNet训练和测试的数据库。 发现DeepUFNet模型能够以高精度预测时空壁面压力信息。 预测结果与实验数据之间的比较在统计信息、时间压力变化、功率谱密度、空间分布和时空相关性方面表现出一致性。 还发现，在DeepUFNet模型中嵌入物理高频损失控制系数$\beta$可以显著提高模型在预测时空壁面压力信息方面的性能，特别是在预测高阶频率波动和壁面压力方差方面。 此外，通过稀疏的空间信息输入测试了DeepUFNet的外推能力，模型表现出令人满意的外推能力。
The wall pressure is of great importance in understanding the forces and structural responses induced by fluid. Recent works have investigated the potential of deep learning techniques in predicting mean pressure coefficients and fluctuating pressure coefficients, but most of existing deep learning frameworks are limited to predicting a single snapshot using full spatial information. To forecast spatiotemporal wall pressure of flow past a rectangular cylinder, this study develops a physics-aware DeepU-Fourier neural Network (DeepUFNet) deep learning model. DeepUFNet comprises the UNet structure and the Fourier neural network, with physical high-frequency loss control embedded in the model training stage to optimize model performance, where the parameter $\beta$ varies with the development of the training epoch. Wind tunnel testing is performed to collect wall pressures of a two-dimensional rectangular cylinder with a side ratio of 1.5 at an angle of attack of zero using high-frequency pressure scanning, thereby constructing a database for DeepUFNet training and testing. The DeepUFNet model is found to forecast spatiotemporal wall pressure information with high accuracy. The comparison between forecast results and experimental data presents agreement in statistical information, temporal pressure variation, power spectrum density, spatial distribution, and spatiotemporal correlation. It is also found that embedding a physical high-frequency loss control coefficient $\beta$ in the DeepUFNet model can significantly improve model performance in forecasting spatiotemporal wall pressure information, in particular, in forecasting high-order frequency fluctuation and wall pressure variance. Furthermore, the DeepUFNet extrapolation capability is tested with sparse spatial information input, and the model presents a satisfactory extrapolation ability
- [6] arXiv:2508.03349 [中文pdf, pdf, html, 其他]
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标题： 稳定分层渠道湍流的平均速度剖面标题： Mean velocity profile in stably stratified channel turbulence主题： 流体动力学 (physics.flu-dyn)
蒙诺-奥布霍夫相似理论（MOST）是大气科学中的基石，用于描述稳定边界层中的湍流。 然而，将 MOST 扩展到稳定分层的湍流通道流动并不容易，因为受到固体壁面的限制以及涉及的湍流尺度要小得多。 在本研究中，我们调查了 MOST 在封闭通道中的适用性，并确定了该理论在何处以及在多大程度上仍然有效。 一个关键发现是，半通道高度与奥布霍夫长度的比值作为确定不同流动区域和其中平均速度尺度的控制参数。 因此，我们提出了一种闭合关系，可以直接从控制输入参数：摩擦雷诺数和摩擦理查森数（$Re_{\tau}$和$Ri_{\tau}$）来估计这个比值。 该框架针对一系列直接数值模拟（DNS）进行了测试，覆盖了$Re_{\tau}$和$Ri_{\tau}$的范围。 重建的速度剖面能够准确预测皮肤摩擦系数，这对于量化工程应用中分层流动的压力损失至关重要。
The Monin-Obukhov Similarity Theory (MOST) is a cornerstone of atmospheric science for describing turbulence in stable boundary layers. Extending MOST to stably stratified turbulent channel flows, however, is non-trivial due to confinement by solid walls and the much smaller turbulent length scales involved. In this study, we investigate the applicability of MOST in closed channels and identify where and to what extent the theory remains valid. A key finding is that the ratio of the half-channel height to the Obukhov length serves as a governing parameter for identifying distinct flow regions and determining the scaling of the mean velocity within them. Hence, we propose a closure relation to estimate this ratio directly from the governing input parameters: friction Reynolds and friction Richardson numbers ($Re_{\tau}$ and $Ri_{\tau}$). The framework is tested against a series of direct numerical simulations (DNS) across a range of $Re_{\tau}$ and $Ri_{\tau}$. The reconstructed velocity profiles enable accurate prediction of the skin friction coefficient crucial for quantifying pressure losses in stratified flows in engineering applications.
- [7] arXiv:2508.03362 [中文pdf, pdf, html, 其他]
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标题： EVP流体绕圆柱体流动的相干结构标题： The coherent structures of EVP Fluid Flow Past a Circular Cylinder主题： 流体动力学 (physics.flu-dyn)
本研究探讨了弹性与塑性对雷诺数为$Re = 100$的二维绕圆柱流动的影响。 使用 Saramito-Herschel-Bulkley 模型进行了十次直接数值模拟，以表示粘弹性及弹粘塑性（EVP）流体。 流动从周期性的冯·卡门涡街演变为类似混沌的流动状态。 采用本征正交分解（POD）和高阶动态模态分解（HODMD）来提取主导流动结构及其时间动力学。 对于粘弹性流体，增加韦森伯格数$Wi$会拉长回流泡并将其向下游移动，导致更复杂的但仍然周期性的行为。 在 EVP 流体中，七个案例研究了宾汉数 Bn、溶剂粘度比$\beta_s$和幂律指数 n 的变化，旨在定性评估它们的影响，而不是确定临界阈值。 结果表明，更强的塑性效应，尤其是当 n>1 时，会导致流动复杂性增加。 识别出三种动态流动状态： (i) 周期性；(ii) 过渡性，具有拉长的回流泡和被破坏的周期性；以及 (iii) 完全复杂性，回流泡破裂。 总体而言，本研究强调了惯性、弹性与屈服应力在障碍物周围非牛顿流体中的相互作用，并确定了驱动周期性到复杂流动状态转变的关键参数。
This study investigates the impact of elasticity and plasticity on two-dimensional flow past a circular cylinder at Reynolds number $Re = 100$. Ten direct numerical simulations were performed using the Saramito-Herschel-Bulkley model to represent viscoelastic and elastoviscoplastic (EVP) fluids. The flow evolves from a periodic von K\'arm\'an vortex street to chaotic-like regimes. Proper Orthogonal Decomposition (POD) and Higher Order Dynamic Mode Decomposition (HODMD) are applied to extract dominant flow structures and their temporal dynamics. For viscoelastic fluids, increasing the Weissenberg number $Wi$ elongates the recirculation bubble and shifts it downstream, resulting in more intricate but still periodic behavior. In EVP fluids, seven cases explore variations in Bingham number Bn, solvent viscosity ratio $\beta_s$, and power law index n, aiming to qualitatively assess their influence rather than determine critical thresholds. Results indicate that stronger plastic effects, especially with n>1, lead to increased flow complexity. Three dynamic regimes are identified: (i) periodic; (ii) transitional, with elongated recirculation and disrupted periodicity; and (iii) fully complex, with breakdown of recirculation. Overall, the study highlights the interplay between inertia, elasticity, and yield stress in non-Newtonian flows past obstacles and identifies key parameters driving the transition from periodic to complex regimes.
- [8] arXiv:2508.03401 [中文pdf, pdf, html, 其他]
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标题： 扩展Duchon-Robert框架以用于异常耗散的可压缩流体流动标题： Extending the Duchon-Robert framework for anomalous dissipation to compressible fluid flows评论： 22页，12图主题： 流体动力学 (physics.flu-dyn)
异常耗散，即当雷诺数趋于无穷大时，平均动能耗散保持有限的现象，在具有足够空间粗糙速度场的流动中会发生。可压缩湍流增加了进一步的异常耗散机制，我们在本工作中进行了研究。为此，将用于异常耗散的Duchon-Robert框架（DR）从不可压缩扩展到可压缩纳维-斯托克斯流动情况。我们得到了三个积分耗散项，其中两个是异常的，一个是粘性的，这些项来源于压力-膨胀和密度变化，这与不可压缩情况不同。随后，对具有行进和相互交叉激波的完全可压缩一维流动进行了详细分析。在这样的流动中，DR在激波前显示了异常耗散的局部最大值。此外，DR与Aluie（AL）提出的可压缩湍流粗粒级联理论进行了比较，两种框架的相关耗散通量项被识别并相互比较。比较结果显示，DR中与可压缩性效应相关的每个贡献在AL中都有其对应项。最后，使用一个分段线性激波型速度剖面，该剖面近似于模拟中两个激波交叉的情况，用于DR异常耗散项的解析分析，以分析这些项对局部Hölder指数的依赖性。我们的工作是对比可压缩湍流中的相干流动结构及相关异常耗散的第一步。
Anomalous dissipation, the persistence of a finite mean kinetic energy dissipation as the Reynolds number tends to infinity, occurs in flows with sufficiently spatially rough velocity fields. Compressible turbulence adds further anomalous dissipation mechanisms, which we investigate in this work. To this end, the Duchon-Robert framework (DR) for anomalous dissipation is extended from the incompressible to the compressible Navier-Stokes flow case. We obtain three integral dissipation terms, two anomalous and a viscous one, which arise from the pressure-dilatation and density variations, differently from the incompressible case. Subsequently, fully compressible one-dimensional flows with traveling and mutually crossing shock waves are analysed in detail. In such flows, DR reveals a local maximum of anomalous dissipation at the shock front. Furthermore, DR is compared with a coarse-grain cascade theory of compressible turbulence due to Aluie (AL) and the relevant dissipation flux terms of both frameworks are identified and compared with each other. The comparison shows that each contribution related to the compressibility effects in DR has its analogue in AL. Finally, a piecewise linear shock-type velocity profile, which approximates the crossing of two shock waves from the simulations, is used for an analytical analysis of the anomalous dissipation terms of DR to analyse the dependence of the terms on the local H\"older exponent. Our work is a first step towards a comparison of coherent flow structures in a compressible turbulent flow and related anomalous dissipation.
- [9] arXiv:2508.03573 [中文pdf, pdf, html, 其他]
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标题： 瞬时磁场增长的最优速度场标题： Optimal velocity fields for instantaneous magnetic field growth主题： 流体动力学 (physics.flu-dyn)
我们考虑运动学发电机问题的一个变种。 而不是指定速度场并通过特征值问题寻找高增长率的磁场，我们将种子磁场结构视为给定，并询问哪个速度场能最大地增强其瞬时增长。 我们表明，这个问题可以通过变分法给出优雅的表述。 在同时约束速度场的动能和涡量的情况下，欧拉-拉格朗日方程导致了一个强制亥姆霍兹偏微分方程（PDE）用于最优速度场。 对于固定动能且无约束涡量的特殊情况，最优速度场在任何地方都与洛伦兹力的不可压缩投影相反。 在更一般的情况下，可以通过数值求解强制亥姆霍兹PDE来找到最优速度场。
We consider a variant of the kinematic dynamo problem. Rather than prescribing a velocity field and searching for high-growth magnetic fields via an eigenvalue problem, we treat the seed magnetic-field structure as given and ask which velocity field maximally enhances its instantaneous growth. We show this second problem has an elegant formulation in terms of variational calculus. Upon simultaneously constraining the velocity's kinetic energy and enstrophy, the Euler-Lagrange equation leads to a forced Helmholtz partial differential equation (PDE) for the optimal velocity field. For the special case of fixed kinetic energy and unconstrained enstrophy, the optimal velocity field everywhere opposes the divergence-free projection of the Lorentz force. In the more general setting, the optimal velocity field can be found through numerical solution of the forced Helmholtz PDE.
新提交 (展示 9 之 9 条目 )
- [10] arXiv:2508.02707 (交叉列表自 math.NA) [中文pdf, pdf, html, 其他]
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标题： 传输噪声在$\mathbb{S}^2$上的扩散行为标题： Diffusive behavior of transport noise on $\mathbb{S}^2$评论： 13页，2张图。欢迎所有评论！主题： 数值分析 (math.NA) ; 概率 (math.PR) ; 流体动力学 (physics.flu-dyn)
我们从理论和数值上研究球面上噪声引起的扩散。 在环面之前的分析表明，适当选择的欧拉方程中的输运噪声会导致类似于纳维-斯托克斯方程的扩散行为。 在这里，我们分析球面上带有噪声引起的微分椭圆算子耗散的动力学，并描述其能量和涡旋度衰减特性。 通过使用Zeitlin离散化的保持结构的数值模拟，我们证明适当缩放的输运噪声会引起能量耗散，同时保持涡旋度和共伴随轨道。 所提出的分析为输运噪声的进一步理论研究奠定了基础，并支持将输运噪声模型校准为地球流体模拟中未解析过程的参数化方法。
We investigate transport theoretically and numerically noise-induced diffusion in flows on the sphere. Previous analysis on the torus demonstrated that suitably chosen transport noise in the Euler equations leads to diffusive behavior resembling the Navier--Stokes equations. Here, we analyze dynamics on the sphere with noise-induced differential elliptic operator dissipation and characterize their energy and enstrophy decay properties. Through structure-preserving numerical simulations with the Zeitlin discretization, we demonstrate that appropriately scaled transport noise induces energy dissipation while preserving enstrophy and coadjoint orbits. The presented analysis lays a groundwork for further theoretical investigation of transport noise and supports the calibration of transport noise models as a parametrization for unresolved processes in geophysical fluid simulations.
- [11] arXiv:2508.02714 (交叉列表自 math.NA) [中文pdf, pdf, html, 其他]
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标题： 样条浅水矩方程标题： Spline Shallow Water Moment Equations主题： 数值分析 (math.NA) ; 偏微分方程分析 (math.AP) ; 流体动力学 (physics.flu-dyn)
由于底层不可压缩纳维-斯托克斯方程的高维度，需要简化的模型来模拟自由表面流动，这些模型需要完全解析垂直方向上的流动以计算表面高度。另一方面，标准的简化模型，如经典的浅水方程（SWE），假设深度与长度比很小并使用深度平均，无法提供关于垂直速度剖面变化的信息。作为折中方案，最近提出的一种使用勒让德多项式作为垂直速度变化的假设函数的浅流矩方法，展示了所谓的浅水矩方程（SWME）的推导，这些方程结合了低维度和速度剖面建模。然而，到目前为止，只考虑了全局多项式。本文引入了样条浅水矩方程（SSWME），其中分段定义的样条假设函数允许以较低的正则性灵活表示速度剖面。样条基函数的局部支撑为适应性和针对一些典型剖面形状的更大灵活性提供了可能性。我们系统地推导和分析了具有不同数量基函数和不同次数的SSWME模型，在此基础上通过进行双曲正则化，并对高阶SSWME模型层次结构的双曲性进行解析证明，推导出一种正则化的双曲版本。数值模拟显示了新模型的高精度和鲁棒性。
Reduced models for free-surface flows are required due to the high dimensionality of the underlying incompressible Navier-Stokes equations, which need to fully resolve the flow in vertical direction to compute the surface height. On the other hand, standard reduced models, such as the classical Shallow Water Equations (SWE), which assume a small depth-to-length ratio and use depth-averaging, do not provide information about the vertical velocity profile variations. As a compromise, a recently proposed moment approach for shallow flow using Legendre polynomials as ansatz functions for vertical velocity variations showed the derivation of so-called Shallow Water Moment Equations (SWME) that combine low dimensionality with velocity profile modeling. However, only global polynomials are considered so far. This paper introduces Spline Shallow Water Moment Equations (SSWME) where piecewise defined spline ansatz functions allow for a flexible representation of velocity profiles with lower regularity. The local support of the spline basis functions opens up the possibility of adaptability and greater flexibility regarding some typical profile shapes. We systematically derive and analyze hierarchies of SSWME models with different number of basis functions and different degrees, before deriving a regularized hyperbolic version by performing a hyperbolic regularization with analytical proof of hyperbolicity for a hierarchy of high-order SSWME models. Numerical simulations show high accuracy and robustness of the new models.
- [12] arXiv:2508.02875 (交叉列表自 cs.CE) [中文pdf, pdf, html, 其他]
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标题： 一种微通道变形和损伤的流体-非局部结构模型标题： A fluid--peridynamic structure model of deformation and damage of microchannels评论： 15页，10图主题： 计算工程、金融与科学 (cs.CE) ; 流体动力学 (physics.flu-dyn)
软壁微通道在许多应用中出现，从芯片上的器官平台到软体机器人执行器。然而，尽管对其静态和动态响应进行了广泛研究，这些设备的潜在故障尚未被解决。为此，我们研究了微通道中的流体-结构相互作用，其柔性的顶壁由一种非局部力学理论控制，该理论能够模拟变形和材料失效。我们通过将润滑近似下的粘性流动与基于状态的无差分动力学公式相结合，开发了一个一维模型，用于欧拉-伯努利梁。无差分动力学公式使壁可以被建模为一个真正的非局部梁，其运动方程的积分形式在变形场是平滑的或包含不连续性时都有效。通过提出的计算模型，我们探讨了这种流体-无差分动力学结构相互作用的稳态和时间依赖行为。我们通过耦合系统的色散（线性化）分析解释了模拟中观察到的波和阻尼动力学，发现随着非局部影响的增加，波传播明显偏离经典行为，表现为相速度的逐渐抑制。本研究的主要贡献是概述了微通道软壁在流动水动力载荷下的潜在故障情景。具体而言，我们在由无量纲斯特劳哈尔数（量化梁的非定常惯性）和柔度数（量化流体-结构耦合强度）所跨越的空间中找到了一条分界曲线，将瞬态条件下的潜在故障情景与稳态载荷下的潜在故障情景区分开来。
Soft-walled microchannels arise in many applications, ranging from organ-on-a-chip platforms to soft-robotic actuators. However, despite extensive research on their static and dynamic response, the potential failure of these devices has not been addressed. To this end, we explore fluid--structure interaction in microchannels whose compliant top wall is governed by a nonlocal mechanical theory capable of simulating both deformation and material failure. We develop a one-dimensional model by coupling viscous flow under the lubrication approximation to a state-based peridynamic formulation of an Euler--Bernoulli beam. The peridynamic formulation enables the wall to be modeled as a genuinely nonlocal beam, and the integral form of its equation of motion remains valid whether the deformation field is smooth or contains discontinuities. Through the proposed computational model, we explore the steady and time-dependent behaviors of this fluid--peridynamic structure interaction. We rationalize the wave and damping dynamics observed in the simulations through a dispersion (linearized) analysis of the coupled system, finding that, with increasing nonlocal influence, wave propagation exhibits a clear departure from classical behavior, characterized by a gradual suppression of the phase velocity. The main contribution of our study is to outline the potential failure scenarios of the microchannel's soft wall under the hydrodynamic load of the flow. Specifically, we find a dividing curve in the space spanned by the dimensionless Strouhal number (quantifying unsteady inertia of the beam) and the compliance number (quantifying the strength of the fluid--structure coupling) separating scenarios of potential failure during transient conditions from potential failure at the steady load.
- [13] arXiv:2508.02933 (交叉列表自 math.AP) [中文pdf, pdf, html, 其他]
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标题： 关于旋转流体的雷利-贝纳德对流问题标题： On the Rayleigh--B\' enard convection problem for rotating fluids评论： 已提交主题： 偏微分方程分析 (math.AP) ; 流体动力学 (physics.flu-dyn)
与热驱动流体的各种传统模型形成对比，我们表明标准的 Oberbeck--Boussinesq 近似\emph{不能}可以作为旋转坐标系中 Navier--Stokes--Fourier 系统的奇异极限得到，其中浮力与重力和离心力之和乘以温度变化成比例。
In contrast with a large variety of conventional models of thermally driven fluids, we show that the standard Oberbeck--Boussinesq approximation \emph{cannot} be obtained as a singular limit of the Navier--Stokes--Fourier system in the rotational coordinate system, with the buoyancy force proportional to the sum of the gravitational and centrifugal forces multiplied by the temperature variation.
- [14] arXiv:2508.03421 (交叉列表自 math.NA) [中文pdf, pdf, 其他]
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标题： 基于伴随方法的物理信息神经网络矩阵预处理框架标题： A matrix preconditioning framework for physics-informed neural networks based on adjoint method评论： 16页，8图主题： 数值分析 (math.NA) ; 流体动力学 (physics.flu-dyn)
物理信息神经网络（PINNs）最近成为解决涉及偏微分方程（PDEs）的正问题和反问题的一种流行方法。 与全连接神经网络相比，基于卷积神经网络的PINNs在硬性执行边界条件和减少偏导数的计算成本方面具有优势。 然而，后者在某些情况下仍存在收敛缓慢甚至失败的问题。 在本研究中，我们提出了一种矩阵预处理方法来改善后者的收敛性。 具体而言，我们将自动微分与矩阵着色相结合，以计算PDE系统的雅可比矩阵，该矩阵通过不完全LU分解用于构建预处理器。 随后，我们使用预处理器对损失函数中的PDE残差进行缩放，以降低雅可比矩阵的条件数，这是提高PINNs收敛性的关键。 为了克服预处理过程中自动微分与三角求解之间的不兼容性，我们还设计了一个基于伴随方法的框架，以计算损失函数相对于网络参数的梯度。 通过数值实验，我们验证了所提出的方法成功且高效地解决了多尺度问题和高雷诺数问题，在这两种问题中，PINNs无法获得满意的结果。
Physics-informed neural networks (PINNs) have recently emerged as a popular approach for solving forward and inverse problems involving partial differential equations (PDEs). Compared to fully connected neural networks, PINNs based on convolutional neural networks offer advantages in the hard enforcement of boundary conditions and in reducing the computational cost of partial derivatives. However, the latter still struggles with slow convergence and even failure in some scenarios. In this study, we propose a matrix preconditioning method to improve the convergence of the latter. Specifically, we combine automatic differentiation with matrix coloring to compute the Jacobian matrix of the PDE system, which is used to construct the preconditioner via incomplete LU factorization. We subsequently use the preconditioner to scale the PDE residual in the loss function in order to reduce the condition number of the Jacobian matrix, which is key to improving the convergence of PINNs. To overcome the incompatibility between automatic differentiation and triangular solves in the preconditioning, we also design a framework based on the adjoint method to compute the gradients of the loss function with respect to the network parameters. By numerical experiments, we validate that the proposed method successfully and efficiently solves the multi-scale problem and the high Reynolds number problem, in both of which PINNs fail to obtain satisfactory results.
- [15] arXiv:2508.03557 (交叉列表自 astro-ph.EP) [中文pdf, pdf, html, 其他]
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标题： 局部三维模拟原行星盘中的对流不稳定性标题： Local three-dimensional simulations of the convective overstability in protoplanetary discs主题： 地球与行星天体物理学 (astro-ph.EP) ; 流体动力学 (physics.flu-dyn)
在某些半径处，原行星盘可能由于局部的不利熵梯度而维持一种振荡对流形式（“对流过稳定性”；COS）。 由此产生的流体动力学活动可以产生相干结构，如带状流和涡旋，这些结构可能集中固体物质并促进其进一步凝聚。 在本文中，我们扩展了之前的轴对称模拟，通过使用代码SNOOPY进行了COS的局部三维模拟。 当参数变化时，我们描述了各种轴对称COS饱和状态如何在三维中转变，同时跟踪它们与次临界热力不稳定的相互关系。 特别是，在低雷诺数（Re）下，我们的三维模拟表现出与我们早期轴对称运行相似的弱非线性和波湍流状态。 在较高Re但低佩克莱特数（Pe）的情况下，我们获得了涉及带状流的形成、随后平面涡旋的发展以及由椭圆不稳定性引起的破坏的爆发性循环。 然而，在较大的Pe情况下，带状流可以持续存在，同时伴随较弱且更细长的涡旋。 这些结果进一步揭示了COS行为的多样性，并表明通过COS诱导的涡旋进行固体积累可能并不简单。
At certain radii protoplanetary discs may sustain a form of oscillatory convection (`convective overstability'; COS) due to localised adverse entropy gradients. The resulting hydrodynamical activity can produce coherent structures, such as zonal flows and vortices, that may concentrate solid material and aid their further coagulation. In this paper we extend previous axisymmetric runs by performing local three-dimensional simulations of the COS, using the code SNOOPY. As parameters are varied, we characterise how the various axisymmetric COS saturated states are transformed in 3D, while also tracking their interrelationship with the subcritical baroclinic instability. In particular, at low Reynolds number (Re) our 3D simulations exhibit similar weakly nonlinear and wave turbulent states to our earlier axisymmetic runs. At higher Re, but low Peclet number (Pe), we obtain bursty cycles involving the creation of zonal flows, the subsequent development of planar vortices, and their destruction by elliptical instability. For larger Pe, however, zonal flows can persist, alongside weaker more elongated vortices. These results further reveal the diversity of the COS's behaviour, and show that solid accumulation via COS-induced vortices may not be straightforward.
交叉提交 (展示 6 之 6 条目 )
- [16] arXiv:2506.20838 (替换) [中文pdf, pdf, html, 其他]
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标题： 摇动液体中液滴运动受历史力的影响标题： Impact of the history force on the motion of droplets in shaken liquids评论： 28页，12图主题： 流体动力学 (physics.flu-dyn)
液滴和固体颗粒在非定常流动中除了受到稳态粘性摩擦、惯性和重力的影响外，还受到Basset-Boussinesq历史力（BBH）的影响。BBH通常被忽略，不是因为这在一般情况下是合理的，而是因为将其包含在计算中通常很困难。为了评估BBH对粒子动力学的重要性，我们重新研究了球形粒子或液滴周围的非定常Stokes流动，并从第一性原理推导出粒子周围速度和作用在它们上的力的解析表达式。这包括气体气泡半径随时间变化的情况，以及如何从围绕粒子的瞬态、扩散驱动的涡旋结构中产生BBH力的图形表示。将这些结果应用于水平摇动流体中重粒子或轻粒子或液滴的沉降（即周期性加速），我们发现，在某些参数范围内，BBH可以使粒子偏转振幅相对于流体运动减少超过60%。我们的（解析）结果表明，BBH效应在低频粘性Stokes区和高频惯性主导区之间的过渡区域变得显著。在此基础上，我们还推导出周期性粒子位移幅度的幂律，该幂律可以明确归因于BBH，并在实验中直接识别。对于轻粒子如气体气泡，惯性力的主要贡献来自附加质量，而BBH对气体气泡的动力学影响比对空气中重粒子或水中金属珠子的情况更为重要。
Droplets and solid particles in unsteady flows are affected by the Basset-Boussinesq history force (BBH), in addition to stationary viscous friction, inertia, and gravity. The BBH is often neglected, not because this is generally justified, but because its inclusion in calculations is usually difficult. To assess the significance of BBH for particle dynamics, we revisit unsteady Stokes flows around spherical particles or droplets and derive from first-principles the analytical expressions for the velocity around the particles and the forces acting on them. This includes the case of time-varying radii for gas bubbles and also graphical representations of how the BBH force arises from transient, diffusion-driven vortex structures around particles. Applying these results to sedimentation of heavy or rising light particles or droplets in horizontally shaken fluids (i.e., periodically accelerated), we find that within certain parameter ranges, BBH can reduce the particle deflection amplitude by more than 60\% relative to the fluid motion. Our (analytical) results show that the BBH effects become large in the transition region between the low-frequency viscous Stokes regime and the regime dominated by high-frequency inertia. On this basis, we also derive a power law for the amplitude of the periodic particle displacement, which can be unambiguously attributed to the BBH and directly identified in experiments. For light particles such as gas bubbles, the dominant contribution to inertial forces comes from the added mass, and the BBH acting on gas bubbles is more important for their dynamics than in the case of heavy particles such as droplets in air or metal beads in water.
- [17] arXiv:2508.02297 (替换) [中文pdf, pdf, 其他]
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标题： 电极中电涡流的理论估计和特性标题： Theoretical estimate and characteristics of electro-vortex flows in cylindrical electrodes评论： 24页，12图主题： 流体动力学 (physics.flu-dyn)
电涡流 (EVF) 是由于电流线的发散和非保守洛伦兹力在导电流体中产生的。它们通常由参数$S$表征，定义为$S=\mu _0 I^2/4\pi^2 \rho \nu^2$，已知当电流较大时$Re \sim \sqrt{S}$。然而，在具有共轴放置电流收集器 (CC) 的受限圆柱形区域内，EVF 的强度还取决于电流收集器半径与圆柱半径的比值$K=r_0/R$，除了电流大小$I$、流体密度$\rho$和运动粘度$\nu$。 对于高$Re$，使用旋度传输方程，我们推导出r.m.s. EVF速度的新理论估计，并发现$u \propto I (1-K)/\sqrt{K}$。我们使用我们在\textsc{开放FOAM}中自建的代码对$K\in[0.1,0.7]$和$I\in[30,555]$A 进行数值模拟来验证我们的估计。此外，对于同一范围，我们将数值结果与文献中可用的最大EVF速度的估计进行比较。我们还讨论了变化的$K$的EVF特性，使用旋度动力学。 最后，我们还提出了一种基于我们速度估计的\emph{修改的}EVF 参数 ($S_M \propto S (1-K)^2/{K}$)，该参数包含$K$。我们的结果表明，比例关系实际上应为$Re \sim \sqrt{S_M}$。
Electro-vortex flows (EVF) arise in conducting fluids due to diverging current lines and the non-conservative Lorentz force. They are typically characterized by the $S$ parameter, defined as $S=\mu _0 I^2/4\pi^2 \rho \nu^2$, where it is known that $Re \sim \sqrt{S}$ for large currents. However, the strength of the EVF in a confined cylindrical domain with a co-axially placed current collector (CC) depends also on the ratio of the CC radius to the cylinder radius, $K=r_0/R$, in addition to the current magnitude, $I$, fluid density, $\rho$ and kinematic viscosity, $\nu$. For high $Re$, using the vorticity transport equation, we derive a new theoretical estimate of the r.m.s. EVF velocity and find that $u \propto I (1-K)/\sqrt{K}$. We validate our estimate with numerical simulations using our custom-built code in \textsc{OpenFOAM} for $K\in[0.1,0.7]$ and $I\in[30,555]$A. In addition, for the same range, we compare our numerical results with the estimates of maximum EVF velocity available in the literature. We also discuss the EVF characteristics for varying $K$ using the vorticity dynamics. Finally, we also propose a \emph{modified} EVF parameter ($S_M \propto S (1-K)^2/{K}$) based on our velocity estimate that includes $K$. Our results suggest that the scaling relationship should actually be $Re \sim \sqrt{S_M}$.
- [18] arXiv:2505.18565 (替换) [中文pdf, pdf, html, 其他]
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标题： 基于物理信息神经网络和浸入边界方法的学习流体-结构相互作用动力学标题： Learning Fluid-Structure Interaction Dynamics with Physics-Informed Neural Networks and Immersed Boundary Methods主题： 机器学习 (cs.LG) ; 计算工程、金融与科学 (cs.CE) ; 流体动力学 (physics.flu-dyn)
我们引入了结合物理信息神经网络（PINNs）与浸入边界方法（IBM）的神经网络架构，以解决流体-结构相互作用（FSI）问题。 我们的方法具有两种不同的架构：一个具有统一参数空间的Single-FSI网络，以及一个创新的欧拉-拉格朗日网络，该网络为流体和结构域保持独立的参数空间。 我们使用标准的Tanh和自适应B样条激活函数来研究每种架构。 在涉及移动固体结构的二维腔体流动问题上的实证研究表明，欧拉-拉格朗日架构表现显著更好。 自适应B样条激活函数通过在边界附近提供局部感知表示进一步提高了准确性。 尽管我们的方法在预测速度场方面表现出色，但由于当前公式中缺乏显式力耦合约束，压力恢复仍然具有挑战性。 我们的研究结果强调了在PINN框架内建模FSI问题时，领域特定的架构设计和自适应激活函数的重要性。
We introduce neural network architectures that combine physics-informed neural networks (PINNs) with the immersed boundary method (IBM) to solve fluid-structure interaction (FSI) problems. Our approach features two distinct architectures: a Single-FSI network with a unified parameter space, and an innovative Eulerian-Lagrangian network that maintains separate parameter spaces for fluid and structure domains. We study each architecture using standard Tanh and adaptive B-spline activation functions. Empirical studies on a 2D cavity flow problem involving a moving solid structure show that the Eulerian-Lagrangian architecture performs significantly better. The adaptive B-spline activation further enhances accuracy by providing locality-aware representation near boundaries. While our methodology shows promising results in predicting the velocity field, pressure recovery remains challenging due to the absence of explicit force-coupling constraints in the current formulation. Our findings underscore the importance of domain-specific architectural design and adaptive activation functions for modeling FSI problems within the PINN framework.