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Machines
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Unsteady Flow Phenomena in Fluid Machinery Systems
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Unsteady Flow Phenomena in Fluid Machinery Systems

A special issue of Machines (ISSN 2075-1702). This special issue belongs to the section "Turbomachinery".

Deadline for manuscript submissions: 30 November 2026 | Viewed by 3158

Special Issue Editors

Prof. Dr. Zhengwei Wang

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Guest Editor
Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
Interests: turbulence; fluid mechanics; fluid machinery; fluid–structure interaction; renewable energy
Special Issues, Collections and Topics in MDPI journals
Dr. Yonggang Lu

E-Mail Website
Guest Editor
School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China
Interests: hydroturbine; pump turbine; gas–liquid two-phase flow; solid–liquid two-phase flow; abrasion; CFD
Special Issues, Collections and Topics in MDPI journals
Dr. Yongyao Luo

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Guest Editor
Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
Interests: hydrodynamics simulation; pump turbine; tidal energy; multi-phase Flow
Special Issues, Collections and Topics in MDPI journals
Dr. Hao Chang

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Guest Editor
Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang 212013, China
Interests: gas–liquid two-phase flow; fluid machinery; pump

Special Issue Information

Dear Colleagues,

Fluid machinery, serving as critical equipment in sectors such as energy, power, chemical processing, and aerospace, directly influences the technological level of major national projects and industrial systems. Within these machines, the presence of highly complex three-dimensional and unsteady turbulent flows represents a fundamental physical phenomenon that limits further improvements in performance and reliability.

Complex turbulent structures within blade passages—such as flow separation, vortex breakdown, secondary flows, and their interactions with wall-bounded boundary layers—are identified as root causes of hydraulic efficiency loss, broad-band vibration, and aerodynamic noise. Furthermore, under challenging operational conditions involving cavitation, particulate matter, multiphase media, or intense heat transfer, the strong coupling between turbulence and other physical phenomena results in highly nonlinear flow characteristics, posing significant threats to operational stability and component service life. Off-design, transient, and extreme operating conditions exacerbate turbulence-induced fluid–structure interaction vibrations, presenting major difficulties in design. With rapid advances in high-performance computing, refined flow measurement techniques, and data science methodologies, new opportunities are emerging for elucidating and controlling turbulent flows in fluid machinery. The integration of Large Eddy Simulation (LES), data-driven modeling, and advanced experimental diagnostics is expected to enable a deeper understanding and accurate prediction of these complex flows, thereby providing a scientific basis for the design of a new generation of highly efficient, low-noise, and reliable fluid machinery.

This Special Issue is dedicated to the topic of turbulence in fluid machinery and aims to collect the latest research achievements in this field. Original contributions are cordially invited from scholars on related fundamental theories, numerical simulations, experimental investigations, and innovative applications. Submissions addressing novel theories, methodologies, and technologies aimed at enhancing the performance and reliability of fluid machinery are particularly encouraged.

Prof. Dr. Zhengwei Wang
Dr. Yonggang Lu
Dr. Yongyao Luo
Dr. Hao Chang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Machines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • fluid machinery
  • turbulence
  • vortex dynamics
  • multiphase flow
  • fluid–structure interaction

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Published Papers (5 papers)

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Research

Jump to: Review

25 pages, 17844 KB  
Article
Effect of Needle Opening on Sediment Erosion and Entropy Production in a Pelton Turbine
by Xijie Song, Zhengwei Wang, Huili Bi, Lianheng Guo, Daqing Qin and Yongxin Liu
Machines 2026, 14(5), 518; https://doi.org/10.3390/machines14050518 - 8 May 2026
Viewed by 178
Abstract
This study investigates how different needle openings govern the coupled evolution of sediment erosion and entropy production-based hydraulic dissipation in a Pelton turbine. Three representative needle openings (20%, 40%, and 54%) are examined by CFD simulation, and the total entropy production is decomposed [...] Read more.
This study investigates how different needle openings govern the coupled evolution of sediment erosion and entropy production-based hydraulic dissipation in a Pelton turbine. Three representative needle openings (20%, 40%, and 54%) are examined by CFD simulation, and the total entropy production is decomposed into wall entropy production, direct dissipation, and indirect dissipation to quantify the opening-dependent irreversibility budget. The results show that the transition zone and buckets consistently dominate the total entropy production, accounting for 84.48%, 80.78%, and 81.57% of the total at 20%, 40%, and 54% openings, respectively, indicating that the nozzle–runner interaction region is the principal carrier of irreversible loss. Meanwhile, reduced opening intensifies jet contraction and promotes non-uniform sediment redistribution, whereas larger openings improve jet coherence and enhance particle flow-following behavior. The wall-level results further reveal that the correspondence between erosion rate density and wall entropy production becomes progressively more evident with increased opening, especially on the bucket pressure side, while particle incidence statistics indicate a transition from broader-angle, locally triggered impacts at small openings to predominantly grazing delivery at larger openings. Overall, the results demonstrate that needle opening does not merely change the magnitude of loss or erosion, but systematically reorganizes the coupled pathway of jet development, sediment redistribution, near-wall dissipation, and wall damage in a Pelton turbine. Full article
(This article belongs to the Special Issue Unsteady Flow Phenomena in Fluid Machinery Systems)
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33 pages, 19699 KB  
Article
Experimental Isolation and Coherence Analysis of Pressure Pulsations in Tubular Pumps: Unveiling the Impact of Impeller Rotation on Flow Dynamics
by Zhaohui Shen, Weipeng Li, Zhenyu Ning, Duoduo Gao, Jiaming Yang, Lijian Shi and Xiaowen Zhang
Machines 2026, 14(1), 101; https://doi.org/10.3390/machines14010101 - 15 Jan 2026
Viewed by 350
Abstract
Tubular pump systems (TPSs) represent a critical class of large-scale turbomachinery for low-head water transport, where mechanical reliability is often challenged by complex internal flow dynamics. Pressure pulsations in pump systems induce vibrations that adversely affect performance, emphasizing the need for effective control [...] Read more.
Tubular pump systems (TPSs) represent a critical class of large-scale turbomachinery for low-head water transport, where mechanical reliability is often challenged by complex internal flow dynamics. Pressure pulsations in pump systems induce vibrations that adversely affect performance, emphasizing the need for effective control mechanisms to ensure stable operation. In tubular pumps, unsteady pressure pulsations are typically driven by rotor–stator interactions; however, the behavior of these pulsations in the absence of impeller rotation remains poorly understood. In this study, a novel comparative investigation is conducted to elucidate the effect of impeller rotation on pressure pulsations characteristic by examining two scenarios: normal impeller operation at rated speed and a completely stationary (zero-speed) impeller condition. Experiments were performed on a model low-head tubular pump, measuring dynamic pressures at four key locations across a range of flow rates. Time–frequency analysis using the continuous wavelet transform (CWT) and the wavelet coherence transform (WTC) was applied to delineate the unsteady pressure features. The results demonstrate that under normal rotation, pressure pulsations are dominated by pronounced periodic components at the impeller’s rotational frequency and its harmonics, with the strongest fluctuation amplitudes observed near the impeller outlet region. In contrast, with the impeller held stationary, these distinct periodic peaks vanish, replaced by broadband, irregular fluctuations. Crucially, WTC analysis revealed that significant coherence between the two operational states was confined to low frequencies (≈16.7–50 Hz), particularly at the impeller inlet, highlighting the presence of low-frequency dynamics likely associated with system-scale hydraulic compliance or inlet flow non-uniformity, independent of impeller rotation. These findings confirm the pivotal role of impeller rotation in generating periodic pressure pulsations while providing new insight into the underlying unsteady flow mechanisms in tubular pumps. Full article
(This article belongs to the Special Issue Unsteady Flow Phenomena in Fluid Machinery Systems)
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28 pages, 14642 KB  
Article
Analysis of Power Regulation Characteristics for Pumped Storage Plants Containing a Variable-Speed Unit with a Full-Size Converter and a Fixed-Speed Unit Considering Hydraulic Disturbances Under Turbine Mode
by Peilin Wu, Weijia Yang, Yiwen Liao, Yufei Teng and Gang Chen
Machines 2026, 14(1), 63; https://doi.org/10.3390/machines14010063 - 4 Jan 2026
Cited by 1 | Viewed by 501
Abstract
The rapid and frequent power regulation of variable-speed pumped storage units with a full-size converter (VSPSU with FSC) causes strong hydraulic disturbances in fixed-speed units (FSU) within shared pipelines. The influence of power command rates on the system has not been sufficiently quantified. [...] Read more.
The rapid and frequent power regulation of variable-speed pumped storage units with a full-size converter (VSPSU with FSC) causes strong hydraulic disturbances in fixed-speed units (FSU) within shared pipelines. The influence of power command rates on the system has not been sufficiently quantified. Therefore, a model of pumped storage plant (PSP) containing VSPSU with FSC and FSU is constructed and validated against internationally used software SIMSEN. Influences of rates on dynamic characteristics are analyzed under turbine power reduction condition. An evaluation method is proposed to quantify power regulation performance for selecting optimal rates. Results indicate the following: (1) Advantage: the VSPSU-FSU demonstrates a superior power response compared to FSU-FSU under fast power control strategy. (2) Influence: overshoots of parameters show positive correlations with rates, while regulation time generally exhibits negative correlations. (3) Evaluation: Power regulation performance has a non-monotonic relationship with rates of VSPSU. Considering rapidity, safety, and stability comprehensively, the performance initially raises to a peak and then declines. Under 50% power reduction, the optimal power command rate is 0.1 p.u./s. The VSPSU–FSU active power regulation time is 4.9 s, significantly lower compared to FSU–FSU (45.17 s). This paper offers crucial insights for optimizing operation of PSPs with VSPSU and FSU. Full article
(This article belongs to the Special Issue Unsteady Flow Phenomena in Fluid Machinery Systems)
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31 pages, 6234 KB  
Article
Research on Cavitation Characteristics of the Fluid Domain of the Single-Plunger Two-Dimensional Electro-Hydraulic Pump
by Xinguo Qiu, Jiahui Wang and Haodong Lu
Machines 2025, 13(12), 1100; https://doi.org/10.3390/machines13121100 - 27 Nov 2025
Viewed by 809
Abstract
A single-plunger two-dimensional electro-hydraulic pump is an integrated unit in which a two-dimensional plunger pump is embedded inside the rotor of a permanent magnet synchronous motor, significantly improving the power density and power-to-weight ratio of electro-hydraulic pumps. The pursuit of a higher power-to-weight [...] Read more.
A single-plunger two-dimensional electro-hydraulic pump is an integrated unit in which a two-dimensional plunger pump is embedded inside the rotor of a permanent magnet synchronous motor, significantly improving the power density and power-to-weight ratio of electro-hydraulic pumps. The pursuit of a higher power-to-weight ratio has made high-speed operation and high-pressure output persistent research priorities. However, during the iterative design process of electro-hydraulic pumps, cavitation has been identified as a common issue, leading to difficulties in oil suction and even severe backflow. Based on the structure and motion characteristics of the single-plunger two-dimensional electro-hydraulic pump, a CFD numerical model was established to analyze the influence of different working conditions on the cavitation characteristics inside the pump. The study shows that cavitation mainly occurs in the plunger chamber, the distribution groove, and the triangular damping groove. The location and intensity of cavitation are directly reflected by the gas volume fraction. The simulation analysis of variable operating conditions has verified that suction pressure and rotational speed have a significant impact on cavitation—an increase in suction pressure can effectively suppress cavitation, while an increase in rotational speed will exacerbate cavitation development. Specifically, the non-cavitation working boundary of this type of pump was determined through theoretical derivation, and the coupling relationship between critical suction pressure and critical speed was clarified. This work provides an important theoretical basis for the optimization design of the new integrated electro-hydraulic pump. Full article
(This article belongs to the Special Issue Unsteady Flow Phenomena in Fluid Machinery Systems)
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Review

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37 pages, 7884 KB  
Review
A Review on Simulation Application Function Development for Computer Monitoring Systems in Hydro–Wind–Solar Integrated Control Centers
by Jingwei Cao, Yuejiao Ma, Xin Liu, Feng Hu, Liwei Deng, Chuan Chen, Yan Ren, Wenhang Zou and Feng Zhang
Machines 2026, 14(1), 87; https://doi.org/10.3390/machines14010087 - 10 Jan 2026
Viewed by 647
Abstract
This paper explores simulation application functions for the computer monitoring system of a hydro–wind–solar integrated control center, focusing on five core areas: platform management, operational training, performance optimization, exception handling, and emergency drills. Against the “dual carbon” backdrop, multi-energy complementary system simulation faces [...] Read more.
This paper explores simulation application functions for the computer monitoring system of a hydro–wind–solar integrated control center, focusing on five core areas: platform management, operational training, performance optimization, exception handling, and emergency drills. Against the “dual carbon” backdrop, multi-energy complementary system simulation faces key challenges including multi-energy coupling, real-time response, and cybersecurity protection. Research shows that integrating digital twin, heterogeneous computing, and artificial intelligence technologies markedly improve simulation accuracy and intelligent decision-making. Dispatch strategies have shifted from single-energy optimization to system-level coordination, while cybersecurity frameworks now provide comprehensive safeguards covering algorithms, data, systems, user behavior, and architecture. Intelligent operation and maintenance with fault diagnosis—powered by big data and deep learning—enables equipment condition prediction, and emergency drill platforms boost response capacity via 3D visualization and scriptless modeling. Current hurdles include absent multi-energy modeling standards, poor extreme-condition adaptability, and inadequate knowledge transfer mechanisms. Future research should prioritize hybrid physical–data-driven approaches, multi-dimensional robust scheduling, federated learning-based diagnostics, and integrated digital twin, edge computing, and decentralized ledger technologies. These advances will drive simulation platforms toward greater intelligence, interoperability, and reliability, laying the technical foundation for unified hydro–wind–solar control centers. Full article
(This article belongs to the Special Issue Unsteady Flow Phenomena in Fluid Machinery Systems)
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