Computers & Fluids最新文献_第5页

A FEM computational approach for gas-liquid flow in pipelines using a two-fluid model

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

Computers & Fluids

Pub Date : 2024-12-06 DOI: 10.1016/j.compfluid.2024.106520

Xiaowei Li , Ruichao Tian , Limin He , Yuling Lv , Shidong Zhou , Yaqiang Li

Two-phase flow is typically observed in gas-liquid pipelines across diverse domains, including nuclear, petroleum, and chemical industries. As accurate prediction of flow characteristics is crucial for engineering applications, one-dimensional two-fluid models with various treatments have been extensively employed to mathematically describe the gas-liquid variations in the pipelines through a set of non-linear partial differential equations (PDEs). This paper presents a modularly designed algorithm that incorporates an implicit scheme coupled with the finite element method (FEM) to solve the one-dimensional two-fluid model with gas-liquid stratified calculation. To validate the accuracy of this algorithm, four cases utilizing varying mesh sizes, inlet flows, and outlet pressures are conducted to scrutinize numerical steady-state gas-liquid flow characteristics, and the consistency between the numerical variations computed through this algorithm and those from OLGA simulator is used to analyze transient gas-liquid behaviors. The steady-state flow fields reveal two distinct zones along the pipe: an intense momentum exchange zone influenced by the inlet nonequilibrium state and a gentle momentum exchange zone influenced by the gas compressibility. Notably, a finer mesh will yield more accurate descriptions of flow parameters in the intense zone, while a relatively sparser mesh suffices for the gentle zone. Additionally, the transient results reveal that the gas-liquid variations in the pipe under initial condition of single-phase gas can be divided into three stages: the gas expansion stage determined by gas compressibility, the gas spread stage influenced by the gas propulsion, and the liquid filling stage decided by the liquid kinetic motion. The consistent identification of the three stages in gas-liquid variations under initial conditions of different static fluids highlights the effectiveness and accuracy of the proposed numerical method in describing transient features.

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引用次数: 0

Parallel large eddy simulations with curvilinear immersed boundary method for high-speed flows

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

Computers & Fluids

Pub Date : 2024-12-06 DOI: 10.1016/j.compfluid.2024.106495

Amir M. Akbarzadeh, Iman Borazjani

A sharp-interface immersed boundary method is developed to simulate turbulent compressible flows through large-eddy simulations (LES) on curvilinear grids. The curvilinear grid enables increasing the grid resolution near regions of interest such as solid walls. To capture both shocks and turbulence, the equations are discretized using a hybrid discretization comprising a fourth-order skew-central scheme and a third-order weighted essentially nonoscillatory (WENO) scheme. A switch function is incorporated to switch between WENO in the vicinity of shocks to central far away from shocks. A dynamics Smagornisky model is used to model the subgrid scales for the central scheme. The interpolation for the immersed boundary is modified to incorporate wall functions. The code is parallelized to efficiently run on thousands of CPU cores for highly resolved grids. The method is verified and validated against several test cases including a decaying isotropic turbulent flow, turbulent channel flow, supersonic flow and shock diffraction over a cylinder. The results show that the LES can properly resolve the inertial subrange and the hybrid scheme can effectively capture shocks over the immersed bodies. It is observed that highly refined grids and low-dissipation hybrid scheme are necessary to capture fine turbulence features such as shear instabilities and shock boundary layer interaction over immersed bodies. In fine grids, however, the importance of explicit LES modeling decreases as most scales are resolved and the WENO scheme provides the dissipation implicitly. In such cases, the results are most sensitive to wall modeling which demonstrate the need for development of wall models for high-speed flows.

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引用次数: 0

A heterogeneous hybrid-precision finite volume method for compressible flow on unstructured grids

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

Computers & Fluids

Pub Date : 2024-12-04 DOI: 10.1016/j.compfluid.2024.106505

Chen Wang, Jian Xia, Long Chen

Single-precision floating-point GPU calculations in modern high-performance heterogeneous computing systems are crucial for increasing the efficiency of large-scale fluid simulations on unstructured grids. However, the lack of a unified programming language for heterogeneous systems and the significant computational errors of single-precision calculations in complex problems pose major challenges. Issues such as poor data locality and data contention in unstructured grid CFD calculations limit GPU performance. Through heterogeneous Kokkos computation, we improved data locality through data reordering and addressed data contention using the scatter-reduce strategy, atomic operations, and the color approach. We introduced an innovative hybrid-precision CFD computation strategy that leverages methods based on object distance and grid geometry for precision blending. This approach harnesses the computational advantages of single-precision GPU calculations while accurately capturing boundary layer information. We assessed the accuracy and performance of these methods on a heterogeneous CPU/GPU computing system. The reverse Cuthill-McKee algorithm significantly enhances performance, atomic operations are the optimal strategy for GPUs, and in the hybrid-precision strategy proposed in this paper, the Tesla A100 GPU, RTX 4090 GPU, and RX 7900 XTX GPU achieve overall speedup of 469, 310, and 413, respectively.

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引用次数: 0

Using Delayed Detached Eddy Simulation to create datasets for data-driven turbulence modeling: A periodic hills with parameterized geometry case

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

Computers & Fluids

Pub Date : 2024-12-04 DOI: 10.1016/j.compfluid.2024.106506

Davide Oberto , Davide Fransos , Stefano Berrone

Despite the emerging field of data-driven turbulence models, there is a lack of systematic high-fidelity datasets at flow configurations changing continuously with respect to geometrical/physical parameters. In this work, we investigate the possibility of using Delayed Detached Eddy Simulation (DDES) to generate reliable datasets in a significantly cheaper manner compared to the DNS or LES counterparts. To do that, we perform 25 simulations of the geometrically-parameterized periodic hills test case to deal with different hills steepnesses. We firstly check the accuracy of our results by comparing one simulation with the benchmark case of Xiao et al. Then, we use such database to train the turbulent viscosity-Vector Basis Neural Network (

ν_{t}

-VBNN) data-driven turbulence model. The latter outperforms the classic

k - ω

SST RANS model, proving that our generated dataset can be useful for data-driven turbulence modeling and opening the opportunity to exploit DDES to create systematic datasets for data-driven turbulence modeling.

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引用次数: 0

Parallel implementation and performance of super-resolution generative adversarial network turbulence models for large-eddy simulation

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

Computers & Fluids

Pub Date : 2024-12-02 DOI: 10.1016/j.compfluid.2024.106498

Ludovico Nista , Christoph D.K. Schumann , Peicho Petkov , Valentin Pavlov , Temistocle Grenga , Jonathan F. MacArt , Antonio Attili , Stoyan Markov , Heinz Pitsch

Super-resolution (SR) generative adversarial networks (GANs) are promising for turbulence closure in large-eddy simulation (LES) due to their ability to accurately reconstruct high-resolution data from low-resolution fields. Current model training and inference strategies are not sufficiently mature for large-scale, distributed calculations due to the computational demands and often unstable training of SR-GANs, which limits the exploration of improved model structures, training strategies, and loss-function definitions. Integrating SR-GANs into LES solvers for inference-coupled simulations is also necessary to assess their a posteriori accuracy, stability, and cost. We investigate parallelization strategies for SR-GAN training and inference-coupled LES, focusing on computational performance and reconstruction accuracy. We examine distributed data-parallel training strategies for hybrid CPU–GPU node architectures and the associated influence of low-/high-resolution subbox size, global batch size, and discriminator accuracy. Accurate predictions require training subboxes that are sufficiently large relative to the Kolmogorov length scale. Care should be placed on the coupled effect of training batch size, learning rate, number of training subboxes, and discriminator’s learning capabilities. We introduce a data-parallel SR-GAN training and inference library for heterogeneous architectures that enables exchange between the LES solver and SR-GAN inference at runtime. We investigate the predictive accuracy and computational performance of this arrangement with particular focus on the overlap (halo) size required for accurate SR reconstruction. Similarly, a posteriori parallel scaling for efficient inference-coupled LES is constrained by the SR subdomain size, GPU utilization, and reconstruction accuracy. Based on these findings, we establish guidelines and best practices to optimize resource utilization and parallel acceleration of SR-GAN turbulence model training and inference-coupled LES calculations while maintaining predictive accuracy.

{"title":"Parallel implementation and performance of super-resolution generative adversarial network turbulence models for large-eddy simulation","authors":"Ludovico Nista , Christoph D.K. Schumann , Peicho Petkov , Valentin Pavlov , Temistocle Grenga , Jonathan F. MacArt , Antonio Attili , Stoyan Markov , Heinz Pitsch","doi":"10.1016/j.compfluid.2024.106498","DOIUrl":"10.1016/j.compfluid.2024.106498","url":null,"abstract":"<div><div>Super-resolution (SR) generative adversarial networks (GANs) are promising for turbulence closure in large-eddy simulation (LES) due to their ability to accurately reconstruct high-resolution data from low-resolution fields. Current model training and inference strategies are not sufficiently mature for large-scale, distributed calculations due to the computational demands and often unstable training of SR-GANs, which limits the exploration of improved model structures, training strategies, and loss-function definitions. Integrating SR-GANs into LES solvers for inference-coupled simulations is also necessary to assess their <em>a posteriori</em> accuracy, stability, and cost. We investigate parallelization strategies for SR-GAN training and inference-coupled LES, focusing on computational performance and reconstruction accuracy. We examine distributed data-parallel training strategies for hybrid CPU–GPU node architectures and the associated influence of low-/high-resolution subbox size, global batch size, and discriminator accuracy. Accurate predictions require training subboxes that are sufficiently large relative to the Kolmogorov length scale. Care should be placed on the coupled effect of training batch size, learning rate, number of training subboxes, and discriminator’s learning capabilities. We introduce a data-parallel SR-GAN training and inference library for heterogeneous architectures that enables exchange between the LES solver and SR-GAN inference at runtime. We investigate the predictive accuracy and computational performance of this arrangement with particular focus on the overlap (halo) size required for accurate SR reconstruction. Similarly, <em>a posteriori</em> parallel scaling for efficient inference-coupled LES is constrained by the SR subdomain size, GPU utilization, and reconstruction accuracy. Based on these findings, we establish guidelines and best practices to optimize resource utilization and parallel acceleration of SR-GAN turbulence model training and inference-coupled LES calculations while maintaining predictive accuracy.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"288 ","pages":"Article 106498"},"PeriodicalIF":2.5,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Optimized dynamic similarity models to predict SGS backscatter in 2D decaying turbulence

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

Computers & Fluids

Pub Date : 2024-11-30 DOI: 10.1016/j.compfluid.2024.106497

Dandan Wang , Yu-xin Ren , Mengnan Ding

Large eddy simulation (LES) of two-dimensional (2D) turbulence is often used in the geostrophic flows. However, some basic dynamics underlying traditional SGS models are absent in 2D turbulence, e.g. the vortex stretching. Hence, this research proposes an optimized dynamic similarity model (DSM) for the SGS stress, which is constructed through the dynamic procedure based on the Germano identity. In addition, a modification is made to the dynamic mixed model (DMM) for the sake of realizability condition. The optimized DSM is justified in comparison with the DMM, through the a priori and a posteriori verifications, in the context of the 2D decaying turbulence with turbulent Reynolds number of

R e = 3.7 \times 1 0^{4}

and turbulent Mach number of

M_{t} = 0.1

. Special attention is paid to the consistency of the verification procedure, so that the filtering operations used in the direct numerical simulation (DNS) and LES are optimally equivalent. The SGS transport phenomena, especially the SGS backscatter, predicted by these two models are studied in detail. In addition, the optimized DSM and the DMM are extended for the modified SGS transport vectors of passive scalars to show their capability in calculating 2D turbulent mixing. The numerical results show the optimized DSM provides larger correlation coefficient, better locality, and stronger SGS backscsatter than the DMM does, and therefore it is more suitable for the LES of 2D turbulence.

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引用次数: 0

Direct numerical simulations of two-dimensional channel flow with a gap deformity and slip wall

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

Computers & Fluids

Pub Date : 2024-11-30 DOI: 10.1016/j.compfluid.2024.106496

Silvia Ceccacci , Sophie A.W. Calabretto , Christian Thomas , James P. Denier

The effect of surface slip on the dynamics of flow separation induced by a Gaussian-shaped gap deformity in a two-dimensional channel was numerically investigated for Reynolds numbers

Re \in [100, 6000]

. Two gap deformations, denoted wide and narrow, were modelled with dimensions sufficient to generate localised pockets of reversed flow when the channel walls were fully no-slip. The wide gap induces a more intense region of separated flow than the narrow gap but less than that exhibited by similar-sized bumps in a channel (Ceccacci et al., 2022). In addition, the size and magnitude of the separation bubble within each gap deformity plateaued for Reynolds numbers

Re > 3000

. Surface slip with slip length,

λ

, was modelled via a Navier-slip boundary condition. Applying the slip condition to the gap concavity reduces the magnitude and thickness of the separation bubble within the deformation and, for a slip length

λ \approx 0.1

, eliminates separated flow for both gap configurations, which is less than the requirements for the bump configuration (Ceccacci et al., 2022). Moreover, limiting slip to the gap region, achieved the same flow separation control, as that realised by applying slip to the entire wall.

{"title":"Direct numerical simulations of two-dimensional channel flow with a gap deformity and slip wall","authors":"Silvia Ceccacci , Sophie A.W. Calabretto , Christian Thomas , James P. Denier","doi":"10.1016/j.compfluid.2024.106496","DOIUrl":"10.1016/j.compfluid.2024.106496","url":null,"abstract":"<div><div>The effect of surface slip on the dynamics of flow separation induced by a Gaussian-shaped gap deformity in a two-dimensional channel was numerically investigated for Reynolds numbers <span><math><mrow><mi>Re</mi><mo>∈</mo><mrow><mo>[</mo><mn>100</mn><mo>,</mo><mn>6000</mn><mo>]</mo></mrow></mrow></math></span>. Two gap deformations, denoted wide and narrow, were modelled with dimensions sufficient to generate localised pockets of reversed flow when the channel walls were fully no-slip. The wide gap induces a more intense region of separated flow than the narrow gap but less than that exhibited by similar-sized bumps in a channel (Ceccacci et al., 2022). In addition, the size and magnitude of the separation bubble within each gap deformity plateaued for Reynolds numbers <span><math><mrow><mi>Re</mi><mo>></mo><mn>3000</mn></mrow></math></span>. Surface slip with slip length, <span><math><mi>λ</mi></math></span>, was modelled via a Navier-slip boundary condition. Applying the slip condition to the gap concavity reduces the magnitude and thickness of the separation bubble within the deformation and, for a slip length <span><math><mrow><mi>λ</mi><mo>≈</mo><mn>0</mn><mo>.</mo><mn>1</mn></mrow></math></span>, eliminates separated flow for both gap configurations, which is less than the requirements for the bump configuration (Ceccacci et al., 2022). Moreover, limiting slip to the gap region, achieved the same flow separation control, as that realised by applying slip to the entire wall.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"288 ","pages":"Article 106496"},"PeriodicalIF":2.5,"publicationDate":"2024-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Investigation of aerodynamic performance and noise of tip shape clearance in a diagonal flow fan

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

Computers & Fluids

Pub Date : 2024-11-30 DOI: 10.1016/j.compfluid.2024.106471

A. Zijian Mao (毛子鉴) , B. Shuiqing Zhou (周水清) , C. Tianle Zhang (张天乐) , D. Jiacheng He (何嘉成) , E. Weiya Jin (金伟娅) , F. Weiping Feng (冯伟平)

Unlike centrifugal fans, diagonal flow fans have an air inflow direction at a certain angle to the axis, with tip clearance (TC) significantly affecting aerodynamic performance and noise. This study focuses on investigating the effects of four different TC shapes based on blade height (BH) ratios. Large Eddy Simulation (LES) was used to capture the structure and development of tip leakage flow (TLF) and tip leakage vortex (TLV) accurately. Diagonal flow fan casings with different TC shapes were 3D-printed for aerodynamic performance experiments. The results from both numerical simulations and experiments show that diagonal flow fans with Tapering or Parallel TC shapes achieve superior aerodynamic performance compared to other geometries, with a 24.1% variance in flow rate. The study further indicates that different TC shapes significantly influence the flow field, altering the mechanisms governing turbulence transition on the suction side. Compared to the Diverging shape, reducing the TC width decreases the amplitude of the TLV, which in turn reduces the turbulence-affected area while increasing dominant mode frequencies. Experimental results also confirm that the Tapering-Diverging TC shape yields the lowest noise levels, with a 3.6 dB reduction in Sound Pressure Level (SPL).

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引用次数: 0

Exact and efficient search-based wall distance algorithm for partitioned unstructured grids

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

Computers & Fluids

Pub Date : 2024-11-28 DOI: 10.1016/j.compfluid.2024.106494

Jun Seok Oh , Tae Yoon Kung , Kyu Hong Kim

In this paper, we develop a novel search-based wall distance calculation algorithm. The algorithm is highly efficient and satisfies the crucial requirement of exactness in wall distance calculations, taking into account the full geometry of the discretized surface. Unlike conventional search-based algorithms that use element-wise bounding boxes or auxiliary grids, the developed algorithm employs only a set of zero-dimensional reference points representing the elements of the discretized surface. Reference points can be chosen as the centers of faces, the centers of edges, or the vertices. The conservative relation between the approximate distance using one of these references and the exact distance is established, allowing for the efficient extraction of element candidates using only low-level information. The algorithm does not require complex pre-processing of the surface or any information about the query points, ensuring high software modularity. An intuitive load balancing procedure is also proposed to address the load imbalance arising from partitioning-based parallelization. Numerical test demonstrates that the developed algorithm shows three orders of magnitude speed-up compared to exhaustive search and one to two orders of magnitude speed-up compared to other search-based algorithms. It also shows high parallel scalability on partitioned meshes, indicating its feasibility for large-scale problems.

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引用次数: 0

Blade-resolved and actuator line simulations of rotor wakes 旋翼尾迹的叶片解析和致动器线仿真

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

Computers & Fluids

Pub Date : 2024-11-26 DOI: 10.1016/j.compfluid.2024.106477

André F.P. Ribeiro , Thomas Leweke , Aliza Abraham , Jens N. Sørensen , Robert F. Mikkelsen

This work concerns high-fidelity numerical simulations of a rotor wake, with focus on the tip vortices and their stability. Blade-resolved and actuator line lattice-Boltzmann simulations are performed on a symmetric baseline rotor, as well as on a rotor with asymmetries. The asymmetry has the purpose of destabilizing the tip vortices to enhance wake recovery and hence the performance of potential downstream turbines. Limitations in the actuator line method are highlighted, and we show the potential of addressing these limitations with a so-called “preset” actuator line, where the forces are extracted from blade-resolved simulations, or an analytical load model, which as input only requires the thrust and power coefficients. Simulations agree well with experimental results and leapfrogging is captured, even with a coarse actuator line simulation. The asymmetric rotor is shown to improve power in the far-wake by 12%.

这项工作涉及高保真的数值模拟的旋翼尾流，重点是尖涡和他们的稳定性。在对称基线转子和不对称基线转子上分别进行了叶片分辨和致动器线格-玻尔兹曼仿真。这种不对称的目的是破坏叶尖涡的稳定，以增强尾流恢复，从而提高潜在下游涡轮的性能。强调了致动器线方法的局限性，我们展示了通过所谓的“预设”致动器线解决这些局限性的潜力，其中从叶片解析模拟或分析负载模型中提取力，其作为输入只需要推力和功率系数。仿真结果与实验结果吻合较好，即使采用粗致动器线仿真，也能捕捉到跨跃现象。非对称转子被证明可以将远尾流的功率提高12%。

引用次数: 0