Article
Mechanics
Yanchong Duan, Qiang Zhong, Guiquan Wang, Peng Zhang, Danxun Li
Summary: This study investigates the contributions of different scale motions to the mean wall-shear stress in smooth-walled open channel flows, revealing the significant impact of large-scale and very-large-scale motions on the wall-shear stress. Comparisons with closed channel flows show slightly higher and lower contributions in specific wavelength ranges in open channel flows, indicating the important role of free-surface effects in open channel flows. Potential mechanisms are discussed to support the observed differences between the two types of flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Thermodynamics
A. Doehring, T. Kaller, S. J. Schmidt, N. A. Adams
Summary: In this study, well-resolved large-eddy simulations of channel flow were conducted, solving the fully compressible Navier-Stokes equations with an adaptive look-up table method for thermodynamic and transport properties. A physically consistent subgrid-scale turbulence model based on the Adaptive Local Deconvolution Method (ALDM) was incorporated. Special treatment of wall temperatures resulted in strong property variations within the channel geometry, affecting the momentum and thermal boundary layer thicknesses. Different formulations of turbulent Prandtl number were discussed in the context of these strong property variations.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2021)
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
Multidisciplinary Sciences
Linus Engelmann, Josef Hasslberger, Seung-Jin Baik, Markus Klein, Andreas Kempf
Summary: A new benchmark case is presented in this study to evaluate models and methods for direct numerical simulation (DNS) and large-eddy simulation (LES). The Taylor-Green vortex is modified by adding walls and a passive scalar to mimic heat transfer. The case provides clean boundary and initial conditions, making it suitable for assessing LES modeling strategies. The results show that the proposed case features challenging flow dynamics not covered by the default Taylor-Green vortex, justifying its usefulness as a benchmark.
SCIENTIFIC REPORTS
(2023)
Article
Geosciences, Multidisciplinary
Iulian-Alin Rosu, Dragos-Constantin Nica, Marius Mihai Cazacu, Maricel Agop
Summary: By studying multifractal entities and nonlinear behaviors in the framework of scale relativity theory, this research reveals various phenomena and their relationships within the atmospheric system, which can be simulated and explained using mathematical models.
FRONTIERS IN EARTH SCIENCE
(2022)
Article
Mechanics
J. G. Chen, S. L. Tang, T. M. Zhou, Y. Zhou
Summary: This study investigated the very-large-scale motions (VLSMs) observed in the wake of a turbulent cylinder, using two experimental datasets. The results revealed a spectral peak at a low wavenumber in the premultiplied spectra of streamwise velocity and temperature fluctuations, indicating the presence of VLSMs. Further analysis using a proper orthogonal decomposition method confirmed the existence of prolonged coherent structures with the same frequency as the spectral peak.
Article
Mechanics
Sparsh Ganju, Sean C. C. Bailey, Christoph Brehm
Summary: Direct numerical simulations are used to investigate incompressible turbulent channel flow over smooth and sinusoidal roughness walls. The study examines the effects of roughness amplitude and wavelength on the flow, and finds that the interaction between the shear layer and roughness significantly influences the flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jie Yao, Xi Chen, Fazle Hussain
Summary: Well-resolved direct numerical simulations of turbulent open channel flows were performed, and it was found that the flow behavior in the near-wall region is similar to closed channel flows, but differs notably in the outer region. The free surface in open channel flows plays a crucial role in various flow phenomena.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
M. David, A. Toutant, F. Bataille
Summary: Thermal large-eddy simulations (T-LES) of anisothermal and turbulent channel flows in solar receivers for concentrated solar power towers were evaluated using direct numerical simulations (DNS). Four different thermal operating conditions were considered to study the performance of various models, and the accuracy of two-layer mixed models combining the Bardina and AMD models was demonstrated. The results showed good agreement between the T-LES and DNS for the tested meshes.
Article
Physics, Fluids & Plasmas
Yoshinobu Yamamoto, Yukio Kaneda, Yoshiyuki Tsuji
Summary: This paper presents a theory on the position dependence of the energy dissipation rate in the inertial sublayer of turbulent channel flow. The theory provides a formula for small but finite ratios of y/h and l tau/y, at a large but finite friction Reynolds number Re tau = h/l tau. The theory agrees well with the data from direct numerical simulations of turbulent channel flow.
PHYSICAL REVIEW FLUIDS
(2023)
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
Mariangela De Maio, Beatrice Latini, Francesco Nasuti, Sergio Pirozzoli
Summary: In this research, direct numerical simulation (DNS) is used to study turbulent flow in rough pipes. Two types of irregular roughness, grit-blasted and graphite surfaces, are investigated. A wide range of Reynolds numbers is tested, and outer-layer similarity is achieved at high Reynolds numbers despite the large relative roughness. A roughness function and an equivalent sand-grain roughness are defined. The results are compared with those obtained in plane channels, and the computed friction factors behave similarly to Nikuradse's chart. However, there are differences in terms of the friction factor in the laminar region and the critical Reynolds number, which are partly absorbed by using the hydraulic radius as a reference length. The distributions of velocity fluctuations intensities show turbulence isotropization in the near-wall region due to roughness, with influence from the roughness geometry. The calculated equivalent sand-grain roughness height suggests that existing correlations have poor predictive power for surfaces with large relative roughness.
JOURNAL OF FLUID MECHANICS
(2023)
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
Thermodynamics
Xu Zhang, Xin Zeng, Chuangxin He, Yingzheng Liu
Summary: The antifouling mechanism of shark skin was investigated using large-eddy simulation in a fully turbulent flow channel. The study validated the antifouling properties through experimental observations and analyzed the flow characteristics using mean and turbulent statistics. A phenomenological scenario based on instantaneous visualizations of vortical events was proposed to explain the spatiotemporal evolution of turbulent coherent structures. The study found that the flow patterns were driven by periodic emission of hairpin-type vortices, which intensified shear stress and momentum exchange.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Geosciences, Multidisciplinary
S. Y. Huang, J. Zhang, Z. G. Yuan, K. Jiang, Y. Y. Wei, S. B. Xu, Q. Y. Xiong, Z. H. Zhang, R. T. Lin, L. Yu
Summary: Based on high-resolution data from the Magnetospheric Multiscale mission, this study investigates energy dissipation in turbulent reconnection outflow in the terrestrial magnetotail. The results show intermittent dissipation at kinetic scales in the turbulent reconnection outflow, accompanied by electron heating and an increase in temperature in intermittent structures and regions with strong currents.
GEOPHYSICAL RESEARCH LETTERS
(2022)
Article
Astronomy & Astrophysics
A. Riols, F. Rincon, C. Cossu, G. Lesur, G. I. Ogilvie, P. -Y. Longaretti
ASTRONOMY & ASTROPHYSICS
(2015)
Article
Mechanics
Subhandu Rawat, Carlo Cossu, Yongyun Hwang, Francois Rincon
JOURNAL OF FLUID MECHANICS
(2015)
Article
Astronomy & Astrophysics
A. Riols, F. Rincon, C. Cossu, G. Lesur, G. I. Ogilvie, P. -Y. Longaretti
ASTRONOMY & ASTROPHYSICS
(2015)
Article
Mechanics
Subhandu Rawat, Carlo Cossu, Francois Rincon
COMPTES RENDUS MECANIQUE
(2016)
Article
Mechanics
Yongyun Hwang, Ashley P. Willis, Carlo Cossu
JOURNAL OF FLUID MECHANICS
(2016)
Article
Multidisciplinary Sciences
Carlo Cossu, Yongyun Hwang
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
(2017)
Article
Astronomy & Astrophysics
A. Riols, F. Rincon, C. Cossu, G. Lesur, G. I. Ogilvie, P. -Y. Longaretti
ASTRONOMY & ASTROPHYSICS
(2017)
Article
Mechanics
Mathieu Marant, Carlo Cossu
JOURNAL OF FLUID MECHANICS
(2018)
Article
Mechanics
Pierluigi Morra, Onofrio Semeraro, Dan S. Henningson, Carlo Cossu
JOURNAL OF FLUID MECHANICS
(2019)
Article
Energy & Fuels
Carlo Cossu
Summary: By tilting the rotors of wind turbines, the negative effects of wake turbulence on downwind turbines can be reduced, leading to increased overall efficiency of wind farms.
Article
Mechanics
Carlo Cossu
Summary: In this study, the genesis of large-scale coherent rolls in turbulent wall-bounded flows was investigated through linear stability analysis, revealing the importance of modeling turbulent Reynolds stresses for consistent predictions. The onset of large-scale convection was found to be associated with a critical friction Richardson number.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Green & Sustainable Science & Technology
Carlo Cossu
Summary: Wake redirection by tilting the rotors of wind turbines in spanwise-periodic arrays can lead to substantial power gains, especially for positive tilt angles of around 30 degrees. The power gains are enhanced by operating the tilted-rotor turbines at higher thrust coefficients, with maximum gains achieved for rotor diameters around 3.6 boundary layer momentum thicknesses. Wind-turbine spanwise spacings that mimic large-scale and very-large-scale streaky motions in turbulent boundary layers can further optimize power generation.
WIND ENERGY SCIENCE
(2021)
Article
Green & Sustainable Science & Technology
Carlo Cossu
Summary: The study reveals that power gains obtained from standard wake redirection can be significantly increased to above 15% by operating tilted or yawed rotors at higher axial induction, potentially tripling the power gains. Even with moderate overinduction, significant enhancements in power gains are obtained.
WIND ENERGY SCIENCE
(2021)
Article
Mechanics
Mathieu Marant, Carlo Cossu, Gregory Pujals
COMPTES RENDUS MECANIQUE
(2017)
Proceedings Paper
Mechanics
Subhandu Rawat, Carlo Cossu, Francois Rincon
24TH INTERNATIONAL CONGRESS OF THEORETICAL AND APPLIED MECHANICS - FOUNDATION OF MULTIDISCIPLINARY RESEARCH
(2017)