Article
Engineering, Marine
Antonio Posa, Riccardo Broglia
Summary: This study analyzes the spanwise distribution of loads on a hydrofoil operating in the wake of a propeller, taking into account the propeller load and the hydrofoil incidence. The results, based on data from Large Eddy Simulations, show that the average loads on the hydrofoil correlate with the radial coordinate of maximum load on the propeller blades. The azimuthal velocity of the propeller wake affects the pressure distribution on the hydrofoil, suggesting that twisted geometries can reduce the local incidence angle and improve the stresses on rudders operating in the wake of propellers.
Article
Thermodynamics
Antonio Posa, Riccardo Broglia
Summary: Large Eddy Simulations were conducted on a system comprising a marine propeller and a hydrofoil to mimic maneuvering conditions in marine propulsion. The study focused on analyzing turbulent fluctuations in the wake downstream of the system. The results showed that the turbulent kinetic energy increased downstream for all configurations, with higher levels observed when the hydrofoil had a higher incidence. Additionally, the cross-stream distribution of turbulence deviated from anti-symmetry due to the different velocities gained by the propeller wake branches while moving across the pressure and suction sides of the hydrofoil.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Mechanics
Debajyoti Kumar, Somnath Roy
Summary: This paper investigates the impact of surface roughness on forces over a cylinder and vortex patterns at low Reynolds numbers. The study uses a novel immersed boundary method to capture small recirculation zones trapped inside roughness elements on the cylinder surface. The results show that the presence of vortices significantly reduces skin-friction drag, and higher roughness height leads to better lock-in phenomena at lower oscillation frequencies. However, the shedding modes of the vortices are not sensitive to surface roughness.
Article
Engineering, Aerospace
Congcong Chen, Yuwei Wang, Zhuo Wang, Lin DU, Xiaofeng Sun
Summary: This study presents an Immersed Boundary Method (IBM) for simulating unsteady turbulent flow in high-Reynolds turbomachinery internal flows. The method demonstrates advantages in grid generation techniques and boundary treatments. The performance of the 2-D and 3-D solvers is validated through testing on low-speed compressor and rotor configurations.
CHINESE JOURNAL OF AERONAUTICS
(2023)
Article
Mechanics
Antonio Posa, Riccardo Broglia, Mario Felli, Marta Cianferra, Vincenzo Armenio
Summary: The acoustic signature of a seven-bladed submarine propeller is characterized using the acoustic analogy method. Results show that the nonlinear terms of the governing equation dominate away from the propeller, while the linear terms decay downstream. The propeller's acoustic signature is mainly tonal in the near field, due to the thickness and loading components of noise from the surface of the propeller and the periodic perturbation caused by its tip vortices. The faster development of instability in the tip vortices compared to the hub vortex leads to an energy cascade towards higher frequencies, contributing to broadband noise.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Alvaro Martinez-Sanchez, Esteban Lopez, Soledad Le Clainche, Adrian Lozano-Duran, Ankit Srivastava, Ricardo Vinuesa
Summary: The aim of this work is to analyze the formation mechanisms of large-scale coherent structures in the flow around a wall-mounted square cylinder and assess the causal relations between different flow modes. Conditional transfer entropy is used to identify the causal relations and understand the origins and evolution of different flow phenomena. The study reveals that vortex-breaker modes are the most causal modes, while no significant causal relationships were found for vortex-generator modes.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Zhaobin Li, Xiaolei Yang
Summary: The study focuses on the similarity of wakes from wind turbines with different yaw angles and tip speed ratios under turbulent inflows. It finds that these wake characteristics overlap when properly normalized, suggesting the decomposition of yawed wind turbine wakes into streamwise and lateral components. Additionally, analytical expressions are proposed to relate instantaneous wake widths and centerline streamwise velocities, aiding in the development of physics-based dynamic wake models.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Computer Science, Interdisciplinary Applications
Antonio Posa, Riccardo Broglia, Elias Balaras
Summary: Large Eddy Simulation is used to replicate the wake of a marine propeller and compared with Particle Imaging Velocimetry experiments. The study focuses on analyzing the tip and hub vortices and their interaction mechanisms. The results reveal that the tip vortices' instability is triggered by their shear with the wake of neighboring blades, leading to oscillations and mutual inductance phenomena. The break-up of the helical structures shed from the tip of the propeller blades increases turbulence at the wake outer boundary, which is further enhanced by the energy provided by the hub vortex. The instability process of the hub vortex is slower but maintains coherence downstream, resulting in a decrease in turbulence at the wake axis.
COMPUTERS & FLUIDS
(2022)
Article
Mechanics
Te-Yao Chiu, Chien-Chou Tseng, Chien-Cheng Chang, Yi-Ju Chou
Summary: This study investigated the influence of coherent structures on the aerodynamic forces acting on an aerofoil. The results showed that these structures have a significant impact on drag and lift forces, and can be identified and quantified using the SPOD algorithm and vorticity force analysis.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Computer Science, Interdisciplinary Applications
Hanane Atmani, Remi Zamansky, Eric Climent, Dominique Legendre
Summary: In this paper, a hybrid IBM-LES method is proposed to simulate high-Reynolds number pipe flows on coarse Cartesian meshes. The IBM method is used to simulate both laminar and turbulent pipe flows, and a new IBW wall boundary condition modeling method is introduced. By adjusting the control parameters, the correct fluid characteristics can be recovered. Furthermore, a stochastic model is used to improve the turbulence level and spatial distribution, and the effects of Reynolds number and grid resolution are discussed.
COMPUTERS & FLUIDS
(2022)
Article
Mechanics
Guodan Dong, Jianhua Qin, Zhaobin Li, Xiaolei Yang
Summary: In this study, the characteristics of wind turbine wakes for three different blade designs were investigated using large-eddy simulations with the actuator surface model. The results show that the blade designs influence the velocity deficit, turbulence kinetic energy, and wake meandering. The NREL-Root design exhibits higher velocity deficit, the NREL-Tip design has higher turbulence kinetic energy in the near wake, and the NREL-Root design has higher turbulence kinetic energy in the far wake.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
Leandro J. L. Stival, Joshua R. Brinkerhoff, Joao Marcelo Vedovotto, Fernando Oliveira de Andrade
Summary: This study applies large eddy simulation (LES) and immersed boundary (IB) method to investigate the flow around wind turbines and validates the results. The research shows that there is a significant loss of kinetic energy in the near wake region of the wind turbine, but the results are similar to the literature in the far wake region.
ENERGY CONVERSION AND MANAGEMENT
(2022)
Article
Construction & Building Technology
Jun Wang, Li Wang, William(Wei) Zhang
Summary: The study focuses on turbulence energy spectrum of fluctuating inflow velocity in LES, proposing a projection algorithm to modify the previous spectrum method. The validated procedure showed better performance and revealed specific oscillation patterns in flow change rate around openings in building natural ventilation design.
BUILDING AND ENVIRONMENT
(2021)
Article
Computer Science, Interdisciplinary Applications
Soonpil Kang, Arif Masud
Summary: This paper presents an immersed boundary method for weak enforcement of Dirichlet boundary conditions on immersed surfaces. The method combines the Variational Multiscale Discontinuous Galerkin method and an interface stabilized form. A significant contribution of this work is the analytically derived Lagrange multiplier for weak enforcement of the Dirichlet boundary conditions. Numerical experiments demonstrate the method's effectiveness with different types of meshes, and the norm of the stabilization tensor varies with the flow physics.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Mechanics
Jianyun Yangzhou, Jiafeng Wu, Zhaokai Ma, Xun Huang
Summary: In this study, the aeroacoustic sources of a two-bladed propeller ingesting an aerofoil wake were investigated using large eddy simulation and two different source identifying approaches. The numerical beamforming approach determined the phase variations of sources at low to mid frequencies and revealed that high-frequency sources are phase-independent. A new near-field aeroacoustic source analysis approach based on the acoustic analogy was developed to improve the spatial resolution of source identification. The proposed analysis approaches extended the capability of computational fluid dynamics and enabled the detailed study of noise generation mechanisms of wake-ingesting propeller noise.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Computer Science, Interdisciplinary Applications
Chiara Piazzola, Lorenzo Tamellini, Riccardo Pellegrini, Riccardo Broglia, Andrea Serani, Matteo Diez
Summary: This paper presents a comparison between two multi-fidelity methods for forward uncertainty quantification in naval engineering. The findings suggest that Multi-Index Stochastic Collocation is preferable with limited computational budget, while adaptive multi-fidelity Stochastic Radial Basis Functions is better suited for larger computational budgets due to its robustness to numerical noise.
ENGINEERING WITH COMPUTERS
(2023)
Article
Computer Science, Interdisciplinary Applications
Antonio Posa, Riccardo Broglia, Elias Balaras
Summary: Large Eddy Simulation is used to replicate the wake of a marine propeller and compared with Particle Imaging Velocimetry experiments. The study focuses on analyzing the tip and hub vortices and their interaction mechanisms. The results reveal that the tip vortices' instability is triggered by their shear with the wake of neighboring blades, leading to oscillations and mutual inductance phenomena. The break-up of the helical structures shed from the tip of the propeller blades increases turbulence at the wake outer boundary, which is further enhanced by the energy provided by the hub vortex. The instability process of the hub vortex is slower but maintains coherence downstream, resulting in a decrease in turbulence at the wake axis.
COMPUTERS & FLUIDS
(2022)
Article
Thermodynamics
Antonio Posa, Riccardo Broglia
Summary: Large Eddy Simulations were conducted on a system comprising a marine propeller and a hydrofoil to mimic maneuvering conditions in marine propulsion. The study focused on analyzing turbulent fluctuations in the wake downstream of the system. The results showed that the turbulent kinetic energy increased downstream for all configurations, with higher levels observed when the hydrofoil had a higher incidence. Additionally, the cross-stream distribution of turbulence deviated from anti-symmetry due to the different velocities gained by the propeller wake branches while moving across the pressure and suction sides of the hydrofoil.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Mechanics
A. Posa, M. Felli, R. Broglia
Summary: The acoustic characteristics generated by a system consisting of a hydrofoil and a downstream propeller are investigated using the acoustic analogy method. The results show that the angle of incidence of the hydrofoil has a significant impact on the acoustic signature of the system. The nonlinear component of sound dominates at small radial coordinates near the wake, while the linear component of sound originates from the surface of the propeller and moves away along the radial direction. The shear between the wakes shed by the hydrofoil and the propeller plays an important role in enhancing the nonlinear sources of sound.
Article
Mechanics
A. Posa, R. Broglia, E. Balaras
Summary: The flow around the rotor of an axial turbine operating in the wake of an upstream one is studied using large-eddy simulation. The results show that the tip vortices shed by the downstream rotor are strongly influenced by the disturbance produced by the wake of the upstream rotor. The development of the downstream rotor wake is faster and very similar across different distances from the upstream rotor.
Article
Engineering, Mechanical
Weidong Dai, Riccardo Broglia, Ignazio Maria Viola
Summary: This paper investigates the passive mitigation of force fluctuations in rotor blades without compromising the mean load. The effectiveness of a mass-spring system for passive pitch control is demonstrated through analytical models and numerical simulations, showing a reduction of over 80% in thrust fluctuations. Moreover, the use of passive pitch blades results in a more sheared wake and faster wake recovery, indicating the potential benefits for various types of turbines and compressors.
JOURNAL OF FLUIDS AND STRUCTURES
(2022)
Article
Mechanics
A. Posa, R. Broglia
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
A. Posa, R. Broglia, M. Felli
Summary: The Ffowcs-Williams and Hawkings acoustic analogy is used to analyze the signature of a system consisting of a propeller and a downstream hydrofoil. The major sources of sound are found to be located at the leading edge of the hydrofoil, due to the impact of the propeller wake. With the exception of a small area around the propeller wake, most noise is generated by the linear, loading sources on the surface of the hydrofoil.
Article
Engineering, Aerospace
Emanuele Spinosa, Riccardo Broglia, Alessandro Iafrati
Summary: This study investigated the hydrodynamics of three different aircraft fuselage models moving underwater using a URANS flow solver, revealing significant differences in spray configuration near the water surface due to varying fuselage transverse curvature. Additionally, the impact of longitudinal curvature changes on suction force generation at the rear of the fuselage was examined, and the forces acting on the models were analyzed.
AEROSPACE SCIENCE AND TECHNOLOGY
(2022)
Article
Computer Science, Interdisciplinary Applications
Riccardo Pellegrini, Jeroen Wackers, Riccardo Broglia, Andrea Serani, Michel Visonneau, Matteo Diez
Summary: A multi-fidelity active learning method is proposed for design optimization problems with noisy evaluations. The method uses a generalized multi-fidelity surrogate model to accurately predict design performance while reducing computational effort. The method adaptsively queries new training data, selecting both design points and fidelity levels based on an active learning approach. Evaluations on various test problems demonstrate the method's superior performance under limited function evaluation budget.
ENGINEERING WITH COMPUTERS
(2023)
Article
Mechanics
Antonio Posa, Riccardo Broglia, Mario Felli, Marta Cianferra, Vincenzo Armenio
Summary: The acoustic signature of a seven-bladed submarine propeller is characterized using the acoustic analogy method. Results show that the nonlinear terms of the governing equation dominate away from the propeller, while the linear terms decay downstream. The propeller's acoustic signature is mainly tonal in the near field, due to the thickness and loading components of noise from the surface of the propeller and the periodic perturbation caused by its tip vortices. The faster development of instability in the tip vortices compared to the hub vortex leads to an energy cascade towards higher frequencies, contributing to broadband noise.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Marine
Antonio Posa, Riccardo Broglia
Summary: This study analyzes the spanwise distribution of loads on a hydrofoil operating in the wake of a propeller, taking into account the propeller load and the hydrofoil incidence. The results, based on data from Large Eddy Simulations, show that the average loads on the hydrofoil correlate with the radial coordinate of maximum load on the propeller blades. The azimuthal velocity of the propeller wake affects the pressure distribution on the hydrofoil, suggesting that twisted geometries can reduce the local incidence angle and improve the stresses on rudders operating in the wake of propellers.
Article
Engineering, Marine
Antonio Posa, Mario Felli, Riccardo Broglia
Summary: The acoustic analogy is used to analyze the sound generated by a propeller-rudder system, revealing the significant impact of the downstream hydrofoil on sound pressure levels. The hydrofoil's loading noise and the complexity of the wake topology contribute to this effect. Increasing incidence angles result in an elongated wake and higher cross-stream velocity, strengthening the shear between the wakes produced by the propeller and the hydrofoil. The acoustic signature exhibits a complex directivity that varies across azimuthal and streamwise directions.
Article
Mechanics
A. Posa, R. Broglia
Summary: The Ffowcs-Williams and Hawkings acoustic analogy was used to analyze the acoustic characteristics of a tip-loaded propeller with winglets. Large-Eddy Simulations were conducted and the results showed that the rise of acoustic pressure exhibited a logarithmic growth as the rotational speeds of the propeller increased. The turbulent fluctuations on the propeller surface and in its wake system were identified as the major sources of sound, with different dominance in different radial coordinates.
Article
Mechanics
A. Posa, R. Broglia, E. Balaras, M. Felli
Summary: Large-Eddy Simulations were used to reconstruct the acoustic far field of a propeller-hydrofoil system by utilizing a grid of 3.8 billion points and applying the Ffowcs-Williams and Hawkings acoustic analogy. The results showed that the sound from the surface of the downstream hydrofoil dominated the lowest frequencies, especially in its normal direction. However, at the blade frequency and higher frequencies, the upstream propeller's acoustic signature became more prominent, particularly in the upstream and downstream directions. The minima of sound pressure levels were correlated with the spanwise direction of the hydrofoil. Despite changes in flow conditions for growing incidence angles of the hydrofoil, there was no similar increase in acoustic pressure in the far field, even at large incidence angles and the onset of separation phenomena, which only affected the highest frequencies.
Article
Thermodynamics
Navid Freidoonimehr, Azadeh Jafari, Maziar Arjomandi
Summary: In this study, a high-fidelity flow visualisation technique is used to investigate the resemblance between a turbulent boundary layer generated by different tripping devices in a lab environment and a naturally developed canonical turbulent boundary layer. The study finds that the blockage created by trips is the main factor affecting the turbulence statistics at a certain downstream distance.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
Yuning Wang, Alberto Solera-Rico, Carlos Sanmiguel Vila, Ricardo Vinuesa
Summary: This study proposes a method that combines 6-VAEs for modal decomposition and transformer neural networks for temporal-dynamics prediction in the latent space to develop reduced-order models (ROMs) for turbulent flows. The method achieves high reconstruction accuracy and accurate prediction of temporal dynamics.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
L. Laguarda, S. Hickel, F. F. J. Schrijer, B. W. van Oudheusden
Summary: Wall-resolved large-eddy simulations were used to investigate the Reynolds number effects in supersonic turbulent boundary layers at Mach 2.0. The study covered a wide range of friction Reynolds numbers and identified trends in various statistics and scaling laws. The size and topology of turbulent structures in the boundary layer were examined, with a focus on the outer-layer motions at high Reynolds numbers. The study also assessed the influence of outer-layer structures on near-wall turbulence and the sensitivity of uniform momentum regions to compressibility.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
A. Doehring, T. Kaller, S. J. Schmidt, N. A. Adams
Summary: In this study, well-resolved large-eddy simulations were used to investigate turbulent duct flows with a square cross section. The influence of a modified wall shear stress on the secondary flow was analyzed by artificially modifying the wall shear stress at one of the four walls. The results showed that the modification led to an asymmetrical distribution of the secondary flow source terms, affecting the momentum distribution. Furthermore, the anisotropy of the Reynolds stress tensor, which induces the secondary flow vortices, was significantly affected by the wall shear stress modulation.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
