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Article
Engineering, Marine
Yuchang Zhi et al.
Summary: This research explores the dynamics of propeller wake under a light loading condition using dynamic mode decomposition (DMD) and reconstruction. Stable tip and hub vortices are observed without interacting evolution, and elliptical instabilities occur downstream of the tip vortices. The dominant frequencies identified by DMD are related to the blade passing frequency, and the coherent structures primarily result from the convection of the tip vortices. The reconstructed propeller wake flow shows good agreement with the original flow, indicating the potential of DMD-based flow-field reconstruction for propeller wake prediction and control.
Article
Mechanics
Tianyuan Wang et al.
Summary: The effect of a nozzle on the wake dynamics of a four-bladed propeller in an oblique flow is investigated. The wake characteristics and destabilization mechanisms of a non-ducted propeller (NP) and ducted propeller (DP) in axisymmetric and oblique flow conditions are analyzed. The nozzle plays a crucial role in mitigating asymmetry and weakening wake deflection in oblique flow. More destabilization mechanisms are present in oblique flow, including asymmetric evolution and destabilization of NP wake helixes, interaction between vortex shedding and helixes in DP leeward region, and generation of a tube-shaped wake envelope around the nozzle.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Mechanical
Jianjun Luo et al.
Summary: Significant variation exists in the aerodynamic performances of high-speed trains traveling in different infrastructure scenarios, especially when entering tunnels. This can result in complex dynamic responses.
JOURNAL OF FLUIDS AND STRUCTURES
(2023)
Article
Mechanics
A. Posa
Summary: This study presents large-eddy simulations of a system consisting of a marine propeller and a downstream, infinite spanwise hydrofoil, compared with a similar hydrofoil of limited spanwise extent. The results show good agreement between the two cases with no incidence of the hydrofoil. However, as the incidence angle increases, the end effects become important. Accounting for the limited spanwise extent of the hydrofoil results in the generation of streamwise-oriented vortices, reduced spanwise elongation of the propeller wake, and lower turbulent stresses on the suction side of the hydrofoil.
Article
Mechanics
A. Posa
Summary: The Ffowcs-Williams and Hawkings acoustic analogy is used to reconstruct the acoustic signature of two marine propellers, one with winglets at the tip of its blades. A large-eddy simulation database is utilized for computation on a grid of about 5 x 10(9) points. The results show that the propeller with winglets improves thrust and propulsion efficiency by increasing tip-loading, but also reinforces its acoustic signature, mainly due to the loading component of sound from fluctuations of hydrodynamic pressure on its surface.
Article
Engineering, Marine
Han Li et al.
Summary: This study investigated the effects of oblique flow on an underwater propulsor through numerical calculations, showing significant force fluctuations and complex vortex evolution in drifts. The duct experienced the largest force change, with flow separation observed at high drifts.
Article
Mechanics
Denghui Qin et al.
Summary: This paper investigates the effects of the odd and even number of rotor/stator blades on the hydrodynamic performance of a pre-swirl pumpjet propulsor (PJP) through numerical simulations. The study finds that the total unsteady force of the rotor blades is strengthened at the k-order stator-blades-passing frequency when the number of rotor blades is even. Additionally, a phenomenon of rotor-stator resonance is observed when both the rotor and stator numbers are even. These findings provide insights for the design of a PJP.
Article
Mechanics
Hongda Shi et al.
Summary: Modal decomposition techniques, flow field, and spectral analysis are used to investigate the wake dynamics and destabilization mechanisms of a four-bladed marine propeller with or without a nozzle. The presence of the nozzle delays the wake destabilization, changes the wake vortices, and increases the wake length. Modal analysis reveals that the spatial scale of flow phenomena decreases with increasing modal frequency, and the destabilization mechanisms in the wake correspond to specific frequencies.
Article
Mechanics
Lianzhou Wang et al.
Summary: Understanding the dynamics of propeller wakes is crucial for designing and optimizing next-generation propellers. This study investigates the wake instability of a propeller under heavy loading conditions through numerical simulations and modal decomposition techniques, identifying the dominant modes involved.
Article
Mechanics
Antonio Posa
Summary: This study investigates the tip vortices shed by two marine propellers using large-eddy simulation and a cylindrical grid with 5 billion points. It compares a tip-loaded design with winglets against a conventional one at specific operating conditions. The results show that the tip-loaded propeller achieves improved performance but also produces more intense tip vortices. These vortices originate from the edge of each winglet and the junction between the winglets and the blades and merge downstream. The simulations highlight the importance of carefully optimizing the geometry of the winglets to achieve weaker vortices and lower negative pressure peaks at their core.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Cong Sun et al.
Summary: This study analyzed the evolution mechanisms of propeller wakes from near to far field under different inflow conditions. It was found that turbulent inflow contributes to the destabilization process of the tip vortex system by accelerating the interference between adjacent tip-vortex structures and intensifying the instability motion of the tip vortex. The Sparsity-Promoting Dynamic Mode Decomposition (SPDMD) successfully selected the influential dynamic modes for the approximation of the snapshot sequence.
Article
Mechanics
A. Posa
Summary: Large-eddy simulations are used to study the tip vortices shed by a hydrofoil in a system with a propeller. The results show that the tip vortices have a significant impact on the performance, turbulence levels, and pressure fluctuations of the system.
Article
Mechanics
F. Magionesi et al.
Summary: This study analyzes the dynamic response of a marine rudder located in the wake of a propeller using a one-way fluid-structure interaction approach. The results reveal different effects of the vortex generated by the propeller on the static and vibratory response of the rudder.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
A. Posa et al.
Summary: This study investigates the interaction between the wake generated by a propeller and a downstream hydrofoil using large-eddy simulations. The results show that the orientation of the hydrofoil significantly influences the wake, causing spanwise shifts of the tip vortices and an overall contraction on the suction side of the hydrofoil. This leads to higher shear and turbulence, as well as a faster growth of the boundary layer thickness. The evolution of the hub vortex is also affected, with the branches shifting across the span of the hydrofoil in the opposite direction of the tip vortices.
Article
Mechanics
Lianzhou Wang et al.
Summary: The wake instabilities of a propeller operating under turbulent-inflow conditions were studied using the improved delayed detached eddy simulation method, revealing the interaction between turbulence and tip vortices.
Article
Mechanics
Lianzhou Wang et al.
Summary: This study investigates propeller wakes under different loading conditions using the improved delayed detached eddy simulation method and flow decomposition technique. The sparsity-promoting dynamic mode decomposition is utilized to study the onset mechanism of propeller wake instabilities.
Article
Mechanics
A. Di Mascio et al.
Summary: This study analyzes the vortical structures in the wake of a naval propeller operating beneath a free surface using detached-eddy simulation. The results show that the wake topology is similar to open water conditions only for low-loading conditions, while the interaction between the vortex system and the free surface leads to vortex breakdown for high blade loading.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Marine
Jiawei He et al.
Summary: The aim of this paper is to evaluate the accuracy, stability and efficiency of different hybrid turbulence models through benchmark computations. The study finds that hybrid models can accurately predict small-scale motions and complex flow structures, with SST-IDDES performing the best.
Article
Mechanics
Shuwei Zhang et al.
Summary: This paper presents a hybrid method based on the von Karman scale and corrected eddy viscosity to study the unsteady flow structure and pressure pulsation characteristics in a centrifugal pump. The results show that the unstable flow in the impeller is influenced by the inflow state, system rotation, and impeller structure. Different inflow states lead to significant differences in internal flow states and unsteady flow structures between the first-stage and second-stage impellers. The analysis of pressure pulsation mechanisms in centrifugal pumps can help optimize pump design and improve operational stability.
Article
Mechanics
Lianzhou Wang et al.
Summary: This study investigates the flow physics in propeller wakes and finds that turbulent inflow significantly modifies the morphology of the vortex system behind the propeller, leading to instability and diffusion of primary tip vortices shed by the blade tips.
Article
Mechanics
M. Felli
Summary: This study investigates the fundamental mechanisms of interaction between propeller wake vortices and untipped non-lifting wings, revealing the complex interaction between propeller tip and blade trailing vortices and wings under different loading conditions. The behavior of tip vortices is strongly influenced by their interaction with the wing's boundary layer during encounter and early penetration phases, leading to asymmetrical evolution and breakdown of vortex portions along the pressure and suction sides of the wing.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Mechanical
Xiao Hu et al.
Summary: This study models the real maglev train and tube to simulate the aerodynamic characteristics in evacuated tube transportation with and without tracks. The results show that tracks affect flow and heat transfer, as well as the evolution of wake vortex and lift coefficient of the train.
JOURNAL OF FLUIDS AND STRUCTURES
(2021)
Article
Acoustics
Huanxian Bu et al.
Summary: This study investigates the aerodynamic and acoustic properties of dual propellers in close vicinity, finding that there is negligible interactional effect between the propellers in most cases. Numerical simulations are also used to examine the flow field of the dual-propeller configuration, showing that the unsteady wake flow from each propeller is contractive with little mutual effect.
JOURNAL OF SOUND AND VIBRATION
(2021)
Article
Mechanics
Yunqing Liu et al.
Summary: This study investigates the dominant coherent structures in cavitating flow around a Clark-Y hydrofoil using data-driven modal decomposition methods (POD and DMD) and explores the interaction between cavitation and vortex. The results show that the main coherent structures include large-scale cavity-vortex, re-entrant jet, shear layer, and small-scale vortex in the wake, and the flow field can be reconstructed from the most energetic POD or DMD modes.
Article
Mechanics
Lianzhou Wang et al.
Summary: The study investigates propeller wake instability mechanisms using simulation methods, analyzing the flow physics that drive the tip vortex instability process. The research extends understanding of propeller wake instability inception mechanisms under heavy loading conditions.
Article
Engineering, Marine
Guang Yin et al.
Summary: This study numerically investigates the flow around a wall-mounted square structure using Spalart-Allmaras Delayed Detached Eddy Simulations (SADDES). Instantaneous and time-averaged hydrodynamic quantities are analyzed, as well as Reynolds-averaged statistics and vortical structures. Dynamic Mode Decomposition (DMD) is employed to study the flow in the wake region behind the square structure, with a reduced order model constructed to show good agreement with numerical simulation results.
Article
Mechanics
Lianzhou Wang et al.
Summary: In unsteady flow fields of rotating machinery, traditional phase average methods can be misleading in interpreting tip vortex behaviors, leading to an overestimation of turbulent diffusion rates and instability motions.
Article
Mechanics
Denghui Qin et al.
Summary: This study investigates vortex instabilities in the wake of a preswirl pumpjet propulsor through numerical analysis based on detached eddy simulations. By focusing on the rotor's vortex structure, the research reveals the evolution of vortices at different advance coefficients and discusses a unique multi-inductance instability mode of the tip vortex.
Article
Computer Science, Interdisciplinary Applications
Bin Zhang et al.
Summary: The study conducted the first high-order eddy-resolving simulation of flow over a marine propeller using a newly developed high-order sliding-mesh method, which accurately predicted loads and demonstrated low-dissipation advantages. Detailed load analysis identified major loads and their distributions, time, and frequency scales, while evaluating the effects of different fairwaters on overall performance.
COMPUTERS & FLUIDS
(2021)
Article
Mechanics
Lianzhou Wang et al.
Summary: This paper investigates the inception mechanism of propeller wake instability, finding that it results from interactions among vortex structures behind the propeller and the high-speed shear layer, with the diffusion of azimuthal velocity playing an important role in the mutual induction process.
Article
Mechanics
Jie Gong et al.
Summary: The study focuses on investigating the wake dynamics of a ducted propeller using detached eddy simulations, revealing the impacts of blade-blade interference and blade-duct interaction on loading stability and efficiency. Short-wave instability governs the wake, with multi-induction effects and duct characteristics influencing the tip vortex system differently.
Article
Mechanics
Lianzhou Wang et al.
Summary: This study investigates the inception mechanism of propeller wake instability and finds that the instability is caused by interactions among vortex structures behind the propeller and the high-speed shear layer, with azimuthal velocity diffusion playing an important role in the mutual induction process. A model is proposed that can predict the time and location of vortex pairing.
Article
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Chun-yu Guo et al.
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(2020)
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Xu Chu et al.
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(2020)
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M. Karami et al.
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Ali Amini et al.
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Francesca Magionesi et al.
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(2018)
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Engineering, Ocean
Lianzhou Wang et al.
APPLIED OCEAN RESEARCH
(2017)
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Vito Pasquariello et al.
JOURNAL OF FLUID MECHANICS
(2017)
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R. Mukund et al.
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JOURNAL OF FLUID MECHANICS
(2014)
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Roberto Muscari et al.
COMPUTERS & FLUIDS
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Nathan Chase et al.
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Mikhail S. Gritskevich et al.
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