Article
Mechanics
F. Ghanadi, L. Djenidi
Summary: The behavior of a fully rough-wall turbulent boundary layer under different pressure gradients is studied. It is found that the boundary layer remains in a self-preserving state regardless of the pressure gradient, but different pressure gradients lead to different self-preservation states. The study also reveals that the roughness effect is more significant than the pressure gradient, especially near the wall.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Civil
Mingxiao Xie, Chi Zhang, Jinzhao Li, Shan Li, Zhiwen Yang, Huaqing Zhang, Ke Qu
Summary: The study found that the phase lead in the boundary layer in the large wave flume was less significant compared to previous experiments in oscillatory flow tunnels. Wave-induced Reynolds stress and wave shape asymmetry contribute to the steady streaming in the flow field.
COASTAL ENGINEERING
(2021)
Article
Mechanics
Tie Wei, Zhaorui Li, Tobias Knopp, Ricardo Vinuesa
Summary: Researchers derived an analytical formulation for the mean wall-normal velocity in turbulent boundary layers and validated its accuracy and robustness through comparisons with numerical simulation data. They also investigated the physical significance of the formulation and its connection to predicting the behavior of turbulent boundary layers.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Hangyu Zhu, Chong Pan, Guohua Wang, Yirui Liang, Xiaocang Ji, Jinjun Wang
Summary: Experimental investigation on particle clustering in a particle-laden turbulent boundary layer with moderate frictional Reynolds number (Re-tau = 5500) reveals self-similarity of particle cluster geometries in the log layer, characterized by power law of the probability density functions of cluster areas and y-scaling of their moments. A conceptual model is proposed where particle clusters tend to reside on back ridges of low-momentum attached u-structures, influenced by high-strain from converging sweep-ejection events. Conditional statistics show sand grains with small slip velocities are captured by low-momentum turbulent motions to form clusters.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Tie Wei, Zhaorui Li, Yanxing Wang
Summary: In this study, a novel analytical solution is derived for the mean wall-normal velocity in a turbulent boundary layer without assuming anything about the mean streamwise velocity. An approximate formulation for the mean wall-normal velocity is obtained by neglecting higher-order terms in the exact solution and validated with direct numerical simulations. Simplified mean momentum equations are derived by decomposing the Reynolds shear stress into inner and outer parts based on the force balance in different regions of the boundary layer. The excellent agreement between the approximate formulation and experimental data demonstrates its accuracy.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
Duo Zhang, Xueqiang Yuan, Shijie Liu, Ke Zhu, Weidong Liu
Summary: The study demonstrates that wall temperature has a significant impact on turbulent boundary layer and shock wave interaction, with heating wall causing increased boundary layer thickness and larger vortices, while cooling wall leads to thinner boundary layer and reduced global vorticity.
Article
Geosciences, Multidisciplinary
Changwei Bian, Xiudan Ruan, Haonan Wang, Xiaolei Liu, Wensheng Jiang, Yonggang Jia
Summary: The importance of internal solitary waves (ISWs) in the upper ocean has been confirmed, but their impact on turbulent mixing in the bottom boundary layer lacks direct field observation. A study conducted at the South China Sea slope observed ISWs passing through, increasing the bottom shear stress and turbulent kinetic energy dissipation rate. However, internal tides were found to play a more crucial role in enhancing bottom turbulent mixing.
JOURNAL OF MARINE SYSTEMS
(2022)
Article
Mechanics
Asim Onder, Philip L. -F. Liu
Summary: Direct numerical simulations reveal a nonlinear feedback loop in a solitary wave boundary layer, where the flow selectively responds to broadband perturbations and develops streamwise-elongated streaks. As the streak amplitudes increase, strong vortices are indirectly amplified, leading to more effective stirring of the boundary layer through the lift-up mechanism.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Zhigang Zhang, Fulin Tong, Junyi Duan, Xinliang Li
Summary: This study conducted a direct numerical simulation of an incident shock wave impinging on a 12° supersonic turbulent expansion corner at a 33.2° angle, revealing the significant influence of expansion on the physics of interaction. The expansion led to reduced wall pressure and separation bubble size, affecting the motion induced by the shock. The study also analyzed the evolution of the reattached boundary layer and the generation mechanism of skin friction.
Article
Mechanics
Dinar Zaripov, Vladislav Ivashchenko, Rustam Mullyadzhanov, Renfu Li, Nikolay Mikheev, Christian J. Kaehler
Summary: In this study, the mechanism of near-wall reverse flow (NWRF) events in turbulent duct flow at a relatively low Reynolds number Re-tau around 200 was investigated using direct numerical simulations and particle image velocimetry. A conceptual model was proposed to explain the formation of NWRF events, suggesting they are caused by intense hairpin vortices at the interface between high- and low-momentum flow regions. The similarity of flow topologies associated with NWRF events at Re-tau around 200 with those at higher Reynolds numbers indicates a generality of the proposed mechanism.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Sourabh S. Diwan, Jonathan F. Morrison
Summary: The study proposed a three-layer asymptotic structure for turbulent pipe flow, revealing the existence of a Reynolds-number-invariant logarithmic region for the streamwise mean velocity and variance in terms of intermediate variables. The analysis determined the classical von Karman and Townsend-Perry constants from the intermediate-scaled log-law constants.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Y. X. Wang, K. -S. Choi, M. Gaster, C. Atkin, V. Borodulin, Y. Kachanov
Summary: The experimental investigation in a low-turbulence wind tunnel revealed that artificially initiated turbulent spots in a laminar boundary layer over a flat plate quickly developed into hairpin-like structures, increasing in width, length and height downstream. Only disturbances greater than a threshold value evolved into turbulent spots, while others decayed. The rate of development was also influenced by the duration of initial disturbances. Additionally, the behavior of turbulence generation within a turbulent spot was found to be similar to burst events in a turbulent boundary layer.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Reza Jahanbakhshi
Summary: The study on the entrainment process in a turbulent boundary layer revealed that the growth of the turbulent core is mainly achieved through the mechanisms of nibbling and engulfment. The engulfment of irrotational pockets within the boundary layer plays a key role in turbulent growth, while vorticity stretching in the turbulent sublayer is weaker, leading to a slower rate of entrainment by nibbling.
Article
Mechanics
N. Agastya Balantrapu, Christopher Hickling, W. Nathan Alexander, William Devenport
Summary: Experiments conducted on a body of revolution at a Reynolds number of 1.9 million showed that the boundary layer displayed characteristics of a free-shear layer, with mean flow and turbulence intensity profiles exhibiting self-similarity.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Bradley Gibeau, Sina Ghaemi
Summary: Simultaneous wall-pressure and high-speed particle image velocimetry measurements were used to identify coherent structures responsible for low- and mid-frequency wall-pressure fluctuations in a turbulent boundary layer at a friction Reynolds number of Re-tau = 2600. The study found that very-large-scale motions (VLSMs) and hairpin packets are the dominant sources of wall-pressure fluctuations at the low and mid frequencies, with different mechanisms affecting wall pressure. The transition between VLSMs and hairpin packets coincided with the peak of the wall-pressure spectrum, suggesting a link between pressure sources and frequency domain transitions.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Marco Mazzuoli, Paolo Blondeaux, Giovanna Vittori, Markus Uhlmann, Julian Simeonov, Joseph Calantoni
JOURNAL OF FLUID MECHANICS
(2020)
Article
Engineering, Marine
Pietro Scandura, Carla Faraci, Paolo Blondeaux
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2020)
Article
Environmental Sciences
G. Vittori, P. Blondeaux
WATER RESOURCES RESEARCH
(2020)
Article
Oceanography
Paolo Blondeaux, Giovanna Vittori
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
(2020)
Article
Mechanics
Giovanna Vittori, Paolo Blondeaux, Marco Mazzuoli, Julian Simeonov, Joseph Calantoni
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2020)
Article
Mechanics
Paolo Blondeaux, Giovanna Vittori
Summary: By investigating the stability of the boundary layer generated by the oscillations of a plate, critical values of Reynolds number for instability can be determined, corresponding to the transition from laminar to disturbed laminar, intermittently turbulent, and fully turbulent regimes in the flow.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
C. Peruzzi, D. Vettori, D. Poggi, P. Blondeaux, L. Ridolfi, C. Manes
Summary: This study investigates the alterations in turbulence in open-channel flows caused by the passage of surface waves, using experimental data collected in a laboratory flume facility. By decomposing the velocity signal and proposing a novel outer length scale, the study identifies a genuine overlap layer and provides insights into turbulent statistics in the current-dominated flow region.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Paolo Blondeaux, Jan Oscar Pralits, Giovanna Vittori
Summary: This study investigates the stability of the boundary layer generated at the bottom of a propagating surface wave of small but finite amplitude, with a focus on the linear stability analysis of laminar flow. The results reveal the existence of four different flow regimes: laminar regime, disturbed laminar regime, intermittently turbulent regime, and fully developed turbulent regime, with transitions between them depending on the Reynolds number and direction of flow near the bottom.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Oceanography
B. Sishah, G. Vittori
Summary: This study numerically simulates the oscillatory turbulent flow over two-dimensional vortex ripples at the bottom of sea waves. It finds that the dynamics of vortex shedding becomes complex as the ratio between fluid excursion and ripple wavelength increases. The formation of steady recirculating cells and the generation of horizontal steady streaming are also observed.
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
(2022)
Article
Marine & Freshwater Biology
G. Vittori, P. Blondeaux, E. Foti, R. E. Musumeci, P. Scandura
Summary: Direct numerical simulations were conducted to study the transition from laminar to turbulent flow within the boundary layer generated by a propagating surface wave. Perturbations of the laminar flow were observed when the Reynolds number is slightly smaller than the critical value, with turbulence occurring after the passage of the wave trough. The results suggest that turbulence is present throughout the wave cycle when the Reynolds number is larger than a certain value, falling between 500 and 700.
ESTUARINE COASTAL AND SHELF SCIENCE
(2023)
Article
Engineering, Civil
Paolo Blondeaux, Giovanna Vittori
Summary: In this study, the partial slip boundary condition is used to evaluate the oscillatory flow generated by propagating surface waves near a rough sandy bottom. The laminar flow regime is considered, but with the introduction of an eddy viscosity to account for momentum transfer induced by small vortices and their effect on mixing processes. The slip velocity at the bottom is characterized by both amplitude and phase, which are determined by fitting model results to experimental measurements. The proposed approach is supported by comparison with experimental data.
JOURNAL OF HYDRAULIC ENGINEERING
(2023)
Article
Engineering, Marine
Giovanna Vittori, Paolo Blondeaux, Marco Mazzuoli
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2020)
