Article
Physics, Fluids & Plasmas
Li-Hao Wang, Chun-Xiao Xu, Hyung Jin Sung, Wei-Xi Huang
Summary: The study focused on the wall-attached structures of velocity fluctuations over a traveling wavy boundary at a moderate Reynolds number using large eddy simulation. The structures show self-similarity in height and are affected by the presence of the wavy boundary in terms of turbulent intensity.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Engineering, Environmental
Yu-Ying Huang, Christina W. Tsai
Summary: Eddies have different impacts on the motion of particles within the turbulence boundary layer depending on their length and velocity scales. Attached eddies, particularly the type-A eddies directly attached to the wall, play a significant role in the turbulent kinetic energy and Reynolds shear stresses in the turbulence boundary layer. This study combines the attached eddies hypothesis with the stochastic diffusion particle tracking model to simulate the transport of suspended sediment particles under the influence of attached eddies.
STOCHASTIC ENVIRONMENTAL RESEARCH AND RISK ASSESSMENT
(2023)
Article
Mechanics
A. Apostolidis, J. P. Laval, J. C. Vassilicos
Summary: We found that the Kolmogorov scale-by-scale equilibrium in the intermediate layer of a fully developed turbulent channel flow is only achieved asymptotically around the Taylor length, indicating it is not in an inertial range. Additionally, we analyzed turbulence production and interscale turbulence energy transfer in terms of alignments/anti-alignments of fluctuating velocities, straining/compressive relative motions, forward/inverse interscale transfer/cascade, and homogeneous/non-homogeneous interscale transfer rate contributions. We also proposed leading order scalings for second- and third-order two-point statistics, including the extremum interscale turbulence energy transfer rate and a second-order anisotropic structure function, which acts as a scale-by-scale Reynolds shear stress and determines the scale-by-scale (two-point) turbulence production rate.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Xuebo Li, Guohua Wang, Xiaojing Zheng
Summary: This study investigates the logarithmic decay of turbulence intensity for wall-attached eddies in the spanwise direction, using linear coherence spectrum analysis to separate the coherent and incoherent portions. It identifies how the turbulence intensity scaling parameter increases with the Reynolds number, and provides a parameterization that can be used to enhance existing near-wall models.
Article
Mechanics
Zhen-xun Dong, Chong Pan, Jin-jun Wang, Xian-xu Yuan
Summary: The study aims to provide new insights into the spatial correlation between superstructures (SS) and large-scale motion (LSM) in a turbulent boundary layer (TBL) through reduced-order analysis using proper orthogonal decomposition (POD). A dataset of three-dimensional velocity fields of a TBL is decomposed by POD and the spatial patterns and length scales of the leading-order POD modes are analyzed. A conditional-average method is proposed to represent the typical local geometric patterns of SS, which are mainly contributed to by one specific observation mode. It is found that the core region of SS is composed of large-scale motion-like structures.
Article
Physics, Fluids & Plasmas
Jinyul Hwang, Jae Hwa Lee
Summary: In wall turbulence, the meandering behaviors of large-scale structures play a crucial role in understanding the spatial organization of these structures and improving turbulence modeling. The meandering motions of wall-attached structures have a significant impact on two-point turbulence statistics and two-dimensional spectra. The meandering magnitudes of structures increase with height, leading to a distinct X pattern in the logarithmic region.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Physics, Fluids & Plasmas
Ming Yu, ChunXiao Xu, JianQiang Chen, PengXin Liu, YaLu Fu, XianXu Yuan
Summary: This study proposes a spectral decomposition method to separate the contributions of wall-attached/detached and self-similar/non-self-similar eddies and analyzes their effects on velocity and temperature fluctuations in turbulent channel flows. The results show that different types of eddies have distinct features and impacts in different regions.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Mechanics
Filipe R. Amaral, Andre V. G. Cavalieri, Eduardo Martini, Peter Jordan, Aaron Towne
Summary: A resolvent-based methodology is used to estimate velocity and pressure fluctuations in turbulent channel flows, with optimal results achieved when true forcing statistics are utilized. Comparisons with approximate forcing models show the significant benefit of using true forcing statistics in accurately estimating flow structures.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Hao-Ran Liu, Kai Leong Chong, Rui Yang, Roberto Verzicco, Detlef Lohse
Summary: In this study, we numerically investigate the influence of gas bubbles attached to the hot plate on turbulent Rayleigh-Benard convection. The existence of bubbles reduces the overall heat transfer and changes the boundary layer structure. We observe asymmetric temperature profiles under different parameter conditions, which can be quantitatively explained based on heat flux conservation. We propose the idea of using an equivalent single-phase setup to mimic the system with attached bubbles and validate the predictions by comparing with numerical results. The results can be applied to predict mass transfer in other fields, such as water electrolysis or catalysis.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Thermodynamics
Ming Yu, Alessandro Ceci, Sergio Pirozzoli
Summary: In this study, the structure of pressure fluctuations in turbulent pipe flow was investigated using standard spectral decomposition and proper orthogonal decomposition (POD) techniques. It was found that the mean pressure distribution differs from that in channel flow, and the pressure fluctuations exhibit a wide region with negative logarithmic decay with the wall distance. The presence of wall-attached eddies, which are isotropic in nature, was clearly observed in spectral maps.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Mechanics
Q. Luo, G. Dolcetti, T. Stoesser, S. Tait
Summary: The water surface response to turbulent flow over a backward-facing step is investigated using high-resolution large-eddy simulation (LES). The LES method is validated using experimental data and the analysis reveals the interplay between turbulence structures and the dynamics of the water surface. The water surface deformation is mainly influenced by gravity waves and turbulence-driven forced waves. The study highlights the importance of decomposing water surface fluctuations to understand the underlying flow structure dynamics.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Fulin Tong, Siwei Dong, Jiang Lai, Xianxu Yuan, Xinliang Li
Summary: The study reports the characteristics of wall shear stress and wall heat flux in a supersonic turbulent boundary layer using direct numerical simulation, with an analysis of statistical data and a detailed conditional analysis on extreme fluctuation events. The results show a different mechanism for the generation of extreme positive and negative events in wall heat flux compared to wall shear stress.
Article
Mechanics
A. Apostolidis, J. P. Laval, J. C. Vassilicos
Summary: This study investigates the scalings of turbulence dissipation and turbulence length/time scales in turbulent channel flow. The results suggest that the integral length scales of fluctuating velocities tend to scale with the distance from the wall, while the turbulence dissipation coefficients tend to be constant with increasing Reynolds number. The study also reveals the anti-correlation between the time fluctuations of turbulence dissipation coefficients and the Taylor-length-based Reynolds number.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Multidisciplinary
Omid Babaie Rizvandi, Xing-Yuan Miao, Henrik Lund Frandsen
Summary: The use of Darcy's Law (DL) to approximate flows in channels with circular and arbitrary cross-sections significantly reduces computational resources and improves model stability and convergence. The DL approximations reduce runtime by approximately 40 times compared to RANS, while accurately predicting velocity and pressure distributions in laminar and turbulent flows.
ALEXANDRIA ENGINEERING JOURNAL
(2021)
Article
Mechanics
Edris Bagheri, Bing-Chen Wang
Summary: The radius ratio has a significant impact on the Nusselt numbers and skin friction coefficients of the inner and outer cylinder walls, as well as on the development and interaction of thermal boundary layers. Turbulent heat transfer is more intense on the outer cylinder side, and as the radius ratio decreases, the differences in turbulence statistics between the inner and outer cylinder sides become more pronounced. Additionally, the most energetic turbulent thermal structures have larger characteristic length scales on the inner cylinder side.