Computers & Fluids最新文献

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Numerical investigation on the end effects of the flow past a finite rotating circular cylinder with two free ends 关于流经带两个自由端有限旋转圆柱体的末端效应的数值研究

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-11-06 DOI: 10.1016/j.compfluid.2024.106475

Qiliang Liu, Shuguang Gong, Haishan Lu, Guilan Xie, Zhijian Zuo

This paper studies the impact of the aspect ratio and free end shape on the end effects in the flow past a rotating circular cylinder with two flat, radiused, hemispherical, and conical ends, using the large eddy simulation method at a Reynolds number of

4.6 \times 10^{4}

. The aspect ratio in the range of 6–30 and the rotation rate in the range of 0–3, are investigated. The results show that the mean drag coefficient initially decreases slightly before rapidly increasing with the rotation rate, with a critical rotation rate that rises from 1 to 1.5 as the aspect ratio increases from 6 to 30. In contrast, the mean lift coefficient increases with both the rotation rate and the aspect ratio. When the rotation rate increases and the aspect ratio decreases, the differences between the aerodynamic coefficients of the four end shapes become more pronounced. The flat end results in the highest mean drag and lift coefficients, while the hemispherical end yields the lowest ones. In addition, when the rotation rate increases, the alternate shedding vortices shift to the opposite side. They even disappear and increase the elongated streamwise vortices. Due to the combined impacts of the rotation and end effects, large-scale tip vortices are formed, significantly altering the wake structure. The intense rotation effect results in expanding the strong influence region of the end effects and shrinking (or even removing) the weak influence region.

本文在雷诺数为 4.6×104 的条件下，采用大涡度模拟方法研究了长宽比和自由端形状对流过具有两个平端、半球形端和锥形端旋转圆柱体的末端效应的影响。研究了 6-30 范围内的长宽比和 0-3 范围内的旋转率。结果表明，随着长宽比从 6 增加到 30，临界旋转率从 1 上升到 1.5。相比之下，平均升力系数会随着旋转率和纵横比的增加而增加。当旋转率增加而纵横比减小时，四种端部形状的空气动力系数之间的差异变得更加明显。扁平端产生的平均阻力系数和升力系数最高，而半球形端产生的平均阻力系数和升力系数最低。此外，当旋转速度增加时，交替脱落的漩涡会转向另一侧。它们甚至消失并增加了拉长的流向涡流。在旋转效应和末端效应的共同作用下，形成了大尺度的尖端涡，显著改变了尾流结构。强烈的旋转效应导致末端效应的强影响区扩大，弱影响区缩小（甚至消失）。

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引用次数: 0

On correctly evaluating orders of truncation error for node-centered edge-based schemes 关于正确评估基于节点中心边缘方案的截断误差阶数

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-11-05 DOI: 10.1016/j.compfluid.2024.106470

Cosimo Tarsia Morisco, Hiroaki Nishikawa

In this short note, we present a simple analysis to show that an observed order of truncation error on a regular grid can change, if not correctly evaluated, depending on the choice of the norm and also on the discretization scheme. For a second-order scheme, it can be first order, second order, or anywhere in between. Using the node-centered edge-based discretization as an example, we provide a guide on how to evaluate the order of truncation error correctly: one should evaluate it separately for a set of nodes, where the residual stencil is symmetric and the same at every node, and the rest of nodes.

在这篇短文中，我们通过一个简单的分析表明，在常规网格上观察到的截断误差阶数，如果没有得到正确的评估，会随着规范的选择和离散化方案的不同而发生变化。对于二阶方案，它可以是一阶、二阶或介于两者之间的任何一阶。以以节点为中心的基于边缘的离散化为例，我们为如何正确评估截断误差的阶数提供了指导：我们应该分别评估一组节点和其他节点的截断误差，前者的残余模版是对称的，并且在每个节点上都是相同的。

引用次数: 0

Non-inertial computational framework for long-distance shock-driven object dynamics 长距离冲击驱动物体动力学的非惯性计算框架

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-11-05 DOI: 10.1016/j.compfluid.2024.106474

Dagao Wang , Guilai Han , Meikuan Liu , Zongxian Li

In the realm of dynamic separation problems, the motion of a body triggered by shock interactions is a common phenomenon. This is particularly important in terms of the safe separation of two-stage-to-orbit vehicles, where the motion must remain stable despite long-distance disturbances from shock waves. The flow field in these cases is complex, marked by interactions between hypersonic shock waves and a moving boundary. This leads to significant unsteady effects due to the body's translation and rotation over extended distances. Existing simulation techniques fall short in rapidly and accurately predicting the aerodynamic force and thermal properties for these problems, largely due to the overwhelming computational demands that result from oversize computational domains and the necessity of grid deformation. This paper presents a novel non-deforming grid method to address these challenges. The central concept is to anchor the reference frame to the moving object itself and to approach the problem from a non-inertial frame perspective. This accounts for the motion of the object solely via the inertial source term, circumventing the complexities of mesh manipulation typically required to link flow and motion equations. The moving shock boundary is designed to be closely compatible with selected shock-captured schemes, which reduces non-physical oscillations compared to the traditional method of direct assembly with theoretical shock relations. Other boundary conditions and the solution process are also refined to specifically target the unsteady, shock-dominated flow. These modifications significantly alleviate the computational burden. The effectiveness of the proposed method is demonstrated through several test cases. To showcase the method's practical application, a scenario is simulated wherein an ellipse is dislodged from a wedge by an incident shock wave, covering a long distance. These tests confirm the method's feasibility in aerospace engineering problems.

在动态分离问题领域，由冲击相互作用引发的物体运动是一种常见现象。这对于两级入轨飞行器的安全分离尤为重要，因为在这种情况下，尽管受到冲击波的长距离干扰，运动仍必须保持稳定。这些情况下的流场非常复杂，其特点是高超音速冲击波与运动边界之间的相互作用。由于机体在长距离内的平移和旋转，这导致了严重的不稳定效应。现有的模拟技术无法快速准确地预测这些问题的气动力和热特性，这主要是由于过大的计算域和网格变形的必要性导致了过高的计算要求。本文提出了一种新颖的非变形网格方法来应对这些挑战。其核心理念是将参考框架锚定在运动物体本身，并从非惯性框架的角度来处理问题。这种方法仅通过惯性源项来考虑物体的运动，从而避免了连接流动方程和运动方程通常所需的复杂网格操作。移动冲击边界的设计与选定的冲击捕获方案密切兼容，与直接装配理论冲击关系的传统方法相比，减少了非物理振荡。其他边界条件和求解过程也进行了改进，以专门针对以冲击为主的非稳定流。这些修改大大减轻了计算负担。通过几个测试案例证明了所提方法的有效性。为了展示该方法的实际应用，我们模拟了一个椭圆被入射冲击波从楔形中移开，并覆盖很长一段距离的场景。这些测试证实了该方法在航空航天工程问题中的可行性。

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引用次数: 0

Reduced data-driven turbulence closure for capturing long-term statistics 减少数据驱动的湍流闭合，捕捉长期统计数据

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-11-01 DOI: 10.1016/j.compfluid.2024.106469

Rik Hoekstra , Daan Crommelin , Wouter Edeling

We introduce a simple, stochastic, a-posteriori, turbulence closure model based on a reduced subgrid scale term. This subgrid scale term is tailor-made to capture the statistics of a small set of spatially-integrated quantities of interest (QoIs), with only one unresolved scalar time series per QoI. In contrast to other data-driven surrogates the dimension of the “learning problem” is reduced from an evolving field to one scalar time series per QoI. We use an a-posteriori, nudging approach to find the distribution of the scalar series over time. This approach has the advantage of taking the interaction between the solver and the surrogate into account. A stochastic surrogate parametrization is obtained by random sampling from the found distribution for the scalar time series. We compare the new method to an a-priori trained convolutional neural network on two-dimensional forced turbulence. Evaluating the new method is computationally much cheaper and gives similar long-term statistics.

我们引入了一个简单的随机后验湍流闭合模型，该模型基于一个缩小的子网格尺度项。这种子网格尺度项是专门为捕捉一小部分空间整合的相关量（QoIs）的统计数据而设计的，每个 QoIs 只有一个未解决的标量时间序列。与其他数据驱动的代用指标相比，"学习问题 "的维度从一个不断变化的场缩小到每个 QoI 一个标量时间序列。我们采用后验、推导的方法来寻找标量序列随时间的分布。这种方法的优点是将求解器与代用参数之间的相互作用考虑在内。从找到的标量时间序列分布中随机抽样，即可得到随机代用参数。我们将新方法与先验训练的卷积神经网络在二维强迫湍流上进行了比较。评估新方法的计算成本要低得多，而且能得到相似的长期统计数据。

引用次数: 0

On an explicit method for pre-estimate flux for incompressible flow simulation 关于不可压缩流动模拟通量预估的显式方法

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-10-28 DOI: 10.1016/j.compfluid.2024.106458

Shumian Zhao , Bernhard Stoevesandt , Joachim Peinke

For incompressible Computational Fluid Dynamics (CFD) problems, the finite volume method (FVM) often uses explicit velocity flux to linearise the convection term. This makes the convergence sensitive to the initial velocity field. The pre-estimation of the initial field is a common strategy to stabilise and/or speed up the solving process. A common technique is to pre-solve a potential flow problem. Here we present an alternative method to pre-estimate the initial flow field for incompressible flow problems. The method will be based on explicit cell-wise flux balancing combined with face shear corrections. This distinguishes it from a typical potential flow pre-estimation where no viscous effects are considered. We will also demonstrate the effectiveness of the method in terms of increasing the convergence speed of CFD simulations on the popular open source platform OpenFOAM in both 2d and 3d scenarios.

对于不可压缩计算流体动力学（CFD）问题，有限体积法（FVM）通常使用显式速度通量来线性化对流项。这使得收敛性对初始速度场非常敏感。预估初始场是稳定和/或加快求解过程的常用策略。预求解势流问题是一种常用技术。在这里，我们将介绍一种预估不可压缩流动问题初始流场的替代方法。该方法基于明确的单元通量平衡，并结合面剪切修正。这使它有别于不考虑粘性效应的典型势流预估。我们还将在流行的开源平台 OpenFOAM 上演示该方法在提高二维和三维 CFD 模拟收敛速度方面的有效性。

引用次数: 0

Modal and nonmodal global instabilities of rotating incompressible axisymmetric boundary layer 旋转不可压缩轴对称边界层的模态和非模态全局不稳定性

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-10-28 DOI: 10.1016/j.compfluid.2024.106459

Ramesh Bhoraniya , Mayank Thummar , Zahir Hussain

This study discusses the modal and non-modal global instabilities of the boundary layer produced on a rotating circular cylinder. An investigation was conducted on a flow of in-compressible fluid over a rotating cylinder of fixed length. The rotation effect of a cylinder generates pressure gradient and centrifugal force radially. The Reynolds number (Re) and rotation rate (S) were calculated using the cylinder’s radius. The Spectral collocation approach discretizes the 3D stability equations in cylindrical polar coordinates, resulting in an initial value problem. Computations were performed for azimuthal wave numbers, N = 0, 1, 2, and 3, Re = 2600, 5200, and 20800, and S = 0.0, 0.5, 1.0, and 2.0. The transient energy growth (

G (t)

) and optimal disturbances were computed by appropriately superimposing the global modes. The perturbation structure that maximizes

G (t)

has been analyzed. The S enhances the optimal value of

G (t)

for a specific Re and N. The highest

G (t)

was observed for helical mode

N = 1

at low Re and for axisymmetric mode

N = 0

at higher Re. The disturbances’ spatial structure has been elongated in the shear direction and has grown and intensity as

S

and

R e

have increased. The perturbation structures are qualitatively distinct for

N = 0

and

N = 1

. The energy budget components have been notably impacted by the alterations in the base-flow caused by the influence of

S

本研究讨论了旋转圆筒上产生的边界层的模态和非模态全局不稳定性。研究对象是固定长度的旋转圆柱体上的不可压缩流体流。圆柱体的旋转效应在径向产生压力梯度和离心力。利用圆柱体的半径计算了雷诺数（Re）和旋转率（S）。光谱配位法将三维稳定方程离散到圆柱极坐标中，从而产生一个初值问题。计算的方位角波数为 N = 0、1、2 和 3，Re = 2600、5200 和 20800，S = 0.0、0.5、1.0 和 2.0。通过适当叠加全局模式，计算出瞬态能量增长（G(t)）和最佳扰动。分析了最大化 G(t) 的扰动结构。在低 Re 条件下，螺旋模式 N=1 的 G(t) 最大，而在高 Re 条件下，轴对称模式 N=0 的 G(t) 最大。扰动的空间结构在剪切方向上被拉长，并随着 S 和 Re 的增大而增强。扰动结构在 N=0 和 N=1 时有本质区别。由于 S 的影响，基流发生了变化，能量收支成分受到了明显的影响。

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引用次数: 0

A high-order local correlation based transition model for transonic airfoil flows 基于高阶局部相关性的跨音速翼面流过渡模型

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-10-28 DOI: 10.1016/j.compfluid.2024.106461

Matthias Plath , Florent Renac , Olivier Marquet , Christian Tenaud

Accurate transition modeling is a key ingredient towards the all-time goal of improved aerodynamic performance in the aircraft industry. While several different approaches exist to model transition, local correlation based transition models (LCTM) are one of the most versatile strategies. Many versions of LCTM were proposed in the context of lower order finite volume discretizations, but so far only a few transition models have been brought to higher-order numerical schemes. The present work represents a first attempt of including a one equation LCTM into the high-order discontinuous Galkerin (DG) framework. Several modifications are accessed to improve the model’s robustness and tailor it for transonic airfoil flows. Validation is conducted for a series of test cases, starting with zero pressure gradient flat plates, progressing through high Reynolds number airfoil flows, and concluding with a complex unsteady transonic buffet scenario. All results are compared against experiments and previous numerical references.

精确的过渡建模是飞机工业实现提高气动性能这一全时目标的关键要素。虽然有几种不同的过渡建模方法，但基于局部相关性的过渡模型（LCTM）是最通用的策略之一。在低阶有限体积离散化的背景下提出了许多版本的 LCTM，但迄今为止，只有少数过渡模型被引入到高阶数值方案中。本研究首次尝试将单方程 LCTM 纳入高阶非连续加尔克里林（DG）框架。为了提高模型的鲁棒性并使其适合跨音速机翼流，我们对模型进行了一些修改。对一系列测试案例进行了验证，从零压力梯度平板开始，到高雷诺数机翼流，最后是复杂的非稳态跨声速缓冲情景。所有结果都与实验和以前的数值参考资料进行了比较。

引用次数: 0

GPU parallel implementation of a finite volume lattice Boltzmann method for incompressible flows 针对不可压缩流动的有限体积晶格玻尔兹曼方法的 GPU 并行执行

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-10-26 DOI: 10.1016/j.compfluid.2024.106460

Mengke Wen , Siyuan Shen , Weidong Li

This work presents a graphics processing units (GPU) parallel algorithm of a cell-centered finite volume lattice Boltzmann method (FVLBM) on unstructured meshes. In the present GPU parallel algorithm, the parallelization is performed in the physical space. To reduce the frequency of GPU memory accesses, this algorithm develops coalesced access to GPU memory. In addition, to avoid the race for resources leading to data anomalies, such as dirty read or phantom read etc., and the double counting for flux calculation, the efficient face-based data structure often used for flux calculation in cells in the central processing unit (CPU) version of FVLBM is modified into a face-based data structure used for the fluxes on all faces, followed by a cell-based loop for the final residuals in all cells. Therefore, the proposed GPU parallel algorithm does not need to use the resource lock and retains the high efficiency of the face-based data structure in the fluxes computation to enhance its’ parallel efficiency. Additionally, to demonstrate the computational efficiency of the proposed GPU parallel algorithm, various benchmark studies are performed in this work by the proposed parallel scheme on a double precision NVIDIA GeForce RTX 3090Ti GPU card, including (a) the lid-driven flow in a two-dimensional (2D) square cavity, (b) a 2D flow past a cylinder, and (c) the lid-driven flow in a three-dimensional (3D) cubic cavity. The numerical results show that the proposed GPU parallel algorithm can be as accurate as the original CPU serial scheme with 1 to 2 orders of speedup.

本研究提出了一种在非结构网格上以单元为中心的有限体积晶格玻尔兹曼法（FVLBM）的图形处理器（GPU）并行算法。在本 GPU 并行算法中，并行化是在物理空间中进行的。为了降低 GPU 内存访问频率，该算法开发了对 GPU 内存的聚合访问。此外，为了避免资源争夺导致数据异常（如脏读或幻读等）以及流量计算的重复计算，FVLBM 的中央处理器（CPU）版本中通常用于单元流量计算的基于面的高效数据结构被修改为基于面的数据结构，用于计算所有面上的流量，然后通过基于单元的循环来计算所有单元的最终残差。因此，所提出的 GPU 并行算法无需使用资源锁，并在通量计算中保留了基于面的数据结构的高效率，从而提高了并行效率。此外，为了证明所提出的GPU并行算法的计算效率，本研究利用所提出的并行方案在双精度NVIDIA GeForce RTX 3090Ti GPU卡上进行了各种基准研究，包括（a）二维（2D）方形空腔中的顶盖驱动流动，（b）经过圆柱体的二维流动，以及（c）三维（3D）立方体空腔中的顶盖驱动流动。数值结果表明，所提出的 GPU 并行算法与原来的 CPU 串行方案一样精确，而且速度提高了 1 到 2 个数量级。

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引用次数: 0

Symmetry-preserving discretizations in Lagrangian cell-centered hydrodynamics 拉格朗日细胞中心流体力学中的对称保留离散化

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-10-24 DOI: 10.1016/j.compfluid.2024.106462

Xihua Xu

This paper discusses constructing discretizations in Lagrangian cell-centered hydrodynamics (CCH) that preserve cylindrical symmetry on unequal-angle-zoned grids in two-dimensional Cartesian geometry. We achieve this by modifying the nodal solver (Corot and Mercier, 2018) and updating the total and internal energy equations. The method is a unique solution to the challenging problem of ensuring symmetry in vectors. A criterion is established for determining whether or not this symmetry correction should be applied. We prove that both nodal and zonal quantities maintain a symmetry distribution. Numerical illustrations using unequal-angle initial zoning are presented to demonstrate the efficiency of the scheme.

本文讨论了在二维笛卡尔几何的不等角分区网格上构建拉格朗日细胞中心流体力学（CCH）离散化，以保持圆柱对称性。我们通过修改节点求解器（Corot 和 Mercier，2018 年）和更新总能量和内能方程来实现这一目标。该方法是确保矢量对称性这一难题的独特解决方案。我们建立了一个标准，用于确定是否应用这种对称性修正。我们证明了节点量和带状量都保持了对称分布。使用不等角初始分区进行了数值说明，以展示该方案的效率。

引用次数: 0

A coupled immersed boundary method and wall modelling framework for high-Reynolds number flows over complex terrain 复杂地形上高雷诺数流动的沉浸边界法与壁面建模耦合框架

IF 2.5 3区工程技术 Q3 COMPUTER SCIENCE, INTERDISCIPLINARY APPLICATIONS

Computers & Fluids

Pub Date : 2024-10-23 DOI: 10.1016/j.compfluid.2024.106457

Jay A. Patel , Ankita Maity , Niranjan S. Ghaisas

We present the development and validation of an immersed boundary method (IBM) along with a wall model (WM) to simulate atmospheric boundary-layer flows over complex terrain. The framework presented here has two novel aspects over standard IBM implementations. First, the underlying schemes are global in nature and require specification of values throughout the solid region. Second, to enable high-Reynolds number simulations, a wall model is coupled to the IBM. The proposed numerical framework is shown to have second-order accuracy. The framework is validated by simulating flow over a 2D as well as 3D cosine-squared hill and comparing to previously published experimental results. The mean velocity and turbulence intensity are reproduced accurately by our LES. The flow over the Bolund hill, marked by steep slopes which makes this a challenging test case, is also simulated and results are compared to field observations showing good agreement. The framework also accurately reproduces the turbulent statistics in the wake of a turbine situated on a flat terrain, with the flat terrain modelled using the IBWM framework, thus demonstrating its applicability to high-Reynolds number atmospheric and wind farm flows over complex terrain.

我们介绍了沉浸边界法（IBM）和壁面模型（WM）的开发和验证情况，以模拟复杂地形上的大气边界层流动。与标准的 IBM 实现相比，这里介绍的框架有两个新颖之处。首先，基础方案是全局性的，需要指定整个固体区域的数值。其次，为实现高雷诺数模拟，壁面模型与 IBM 相耦合。研究表明，所提出的数值框架具有二阶精度。通过模拟二维和三维余弦平方山的流动，并与之前公布的实验结果进行比较，验证了该框架的有效性。我们的 LES 准确地再现了平均速度和湍流强度。博伦德山丘上有陡峭的斜坡，这使其成为一个具有挑战性的测试案例，我们也模拟了博伦德山丘上的气流，并将结果与现场观测结果进行了比较，结果显示两者吻合良好。该框架还精确再现了位于平坦地形上的涡轮机尾流中的湍流统计数据，平坦地形使用 IBWM 框架进行建模，从而证明了该框架适用于复杂地形上的高雷诺数大气和风电场气流。

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