Article
Mechanics
Hirotaka Maeyama, Soshi Kawai
Summary: Near-wall turbulence structures and generation in the wall-modelled large-eddy simulation (WMLES) are investigated by comparing with direct numerical simulation (DNS). The near-wall statistical structures producing turbulence are found to exist even in the WMLES, although they are numerically elongated. The near-wall turbulence structures in the WMLES are suggested to be coherent structures with alternating low- and high-speed fluids in the spanwise direction.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
W. Cheng, D. Pullin, R. Samtaney
Summary: We describe wall-resolved and wall-modelled large-eddy simulation of plane Couette flow. The presence of approximately spanwise periodic sets of streamwise rolls is observed in all simulations. Mean streamwise velocity profiles show substantial spanwise variation but collapse well when normalized by local skin-friction velocities. Similar collapse is found for streamwise turbulent intensities. The mean-flow roll energy and circulation decrease monotonically with increasing Reynolds number.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Luca Guastoni, Alejandro Guemes, Andrea Ianiro, Stefano Discetti, Philipp Schlatter, Hossein Azizpour, Ricardo Vinuesa
Summary: Two convolutional neural network models were trained to predict velocity-fluctuation fields in turbulent open-channel flow, with one directly predicting fluctuations and the other reconstructing flow fields using a linear combination of orthonormal basis functions. Both models outperformed traditional methods in predicting nonlinear interactions in the flow.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Seyed Morteza Habibi Khorasani, Ugis Lacis, Simon Pasche, Marco Edoardo Rosti, Shervin Bagheri
Summary: The transpiration-resistance model (TRM) is a set of boundary conditions that can alter near-wall turbulence. It includes slip boundary conditions and a transpiration condition. The transpiration factor, which is the product of slip and transpiration lengths, can be used to characterize rough surfaces.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Akanksha Baranwal, Diego A. Donzis, Rodney D. W. Bowersox
Summary: This study investigates the effects of compressibility on the near-wall asymptotic behavior of turbulent fluxes using a large direct numerical simulation (DNS) database, finding that the behavior of compressible turbulent flow near walls differs from incompressible flow even when mean density variations are considered. As Mach number increases, turbulent fluxes containing wall-normal components exhibit a decrease in slope due to increased dilatation effects, with Ity approaching its high Mach number asymptote at lower Mach numbers than other fluxes.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Philip Hall
Summary: The study investigates the instability of shear flow passing over a wavy wall, where a new kind of cross-flow vortex instability is found to emerge under specific conditions. This instability is associated with the orientation of the wave crests, and modes of wavelength comparable to the wall wavelength grow much faster than modes of wavelength comparable to the viscous layer.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Adrian Lozano-Duran, Navid C. Constantinou, Marios-Andreas Nikolaidis, Michael Karp
Summary: Despite the nonlinear nature of turbulence, evidence shows that part of the energy transfer mechanisms sustaining wall turbulence can be attributed to linear processes. Different scenarios based on linear stability theory, including exponential instabilities, neutral modes, transient growth from non-normal operators and parametric instabilities, are rooted in simplified physical models. Among these, transient growth has been shown to be sufficient for sustaining realistic wall turbulence, while suppressing other linear mechanisms such as exponential instabilities, neutral modes, and parametric instabilities.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Bowen Yang, Zixuan Yang
Summary: Direct numerical simulations of turbulent channel flows up to Re-tau approximately 1000 were performed to investigate the three-dimensional spectrum of wall pressure fluctuations. It was found that the energy-containing part of the spectrum can be well predicted using a random sweeping model for streamwise velocity fluctuations. Neglecting the cross-spectrum between rapid and slow pressure fluctuations causes a maximum error of up to 4.7 dB in the subconvective region for all Reynolds numbers tested. This suggests that the approximation of neglecting the cross-spectrum needs to be carefully applied in low Mach number acoustics.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
S. L. Tang, R. A. Antonia
Summary: The paper introduces a new hypothesis that suggests near-wall small-scale statistics, when suitably normalized, are independent of flow type as well as Reynolds and Peelet numbers. While the available wall turbulence direct numerical simulations data in a channel flow and a boundary layer provide good support for independence with respect to the Reynolds number, more data are needed to fully validate this hypothesis, particularly for higher-order statistics and other types of wall flows with different surface conditions.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
S. L. Tang, R. A. Antonia
Summary: In this paper, we propose a hypothesis that turbulent kinetic energy, Reynolds stresses, and scalar variance in wall-bounded turbulent flows are independent of Reynolds and Peclet numbers when sufficiently large. Two scaling ranges are identified: an inertial-convective range with a 2/3 power-law scaling and a viscous-convective range where the normalized scalar variance remains constant. The hypothesis is supported by available wall turbulence data and the relationship with traditional wall scaling is discussed. Potential ultimate statistical states of wall turbulence are also proposed.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Nuclear Science & Technology
F. Maviglia, M. Siccinio, C. Bachmann, W. Biel, M. Cavedon, E. Fable, G. Federici, M. Firdaouss, J. Gerardin, V Hauer, I. Ivanova-Stanik, F. Janky, R. Kembleton, F. Militello, F. Subba, S. Varoutis, C. Vorpahl
Summary: This work reviews the role of plasma facing components protection in driving the EU-DEMO design, focusing on both steady-state and transient situations. Different protection limiters are implemented to reduce heat load on the first wall and divertor, while alternative divertor configurations are under investigation to mitigate risks during various plasma transients.
NUCLEAR MATERIALS AND ENERGY
(2021)
Article
Physics, Fluids & Plasmas
Yoshiharu Tamaki, Soshi Kawai
Summary: This study proposes an approach of wall-modeled large-eddy simulation on non-body conforming Cartesian grids, addressing the issue of insufficient grid resolution near the wall with partial-slip wall-boundary conditions and modeled turbulent shear stress. Validation experiments and quantification analysis demonstrate the effectiveness and robustness of the method.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Mechanics
Ming Yu, Chunxiao Xu
Summary: In this study, predictive models for near-wall velocity and temperature fluctuations in compressible wall-bounded turbulence are developed based on the model proposed by Marusic et al. The models incorporate the effects of large-scale motions in the outer region on near-wall turbulence and are validated through direct numerical simulations. The results show good agreement between the predicted fluctuations and the actual results.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Aniruddhe Pradhan, Karthik Duraisamy
Summary: The main objective of this work is to develop a unified framework to assess and improve coarse-grained models of turbulence. Using a turbulent channel flow as an example, this study evaluates optimality in different limits and develops accuracy metrics for scale-resolving methods. Furthermore, a universal scaling relationship for slip velocity in wall-modeled LES is characterized, and improved slip-wall models are proposed based on insights from a priori tests.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Yu Lv, Xinyi L. D. Huang, Xiaolei Yang, Xiang I. A. Yang
Summary: The paper addresses performance issues of wall-modeled large-eddy simulation (WMLES) by integrating wall models into LES solvers, abandoning stand-alone wall-model solvers. By employing physics-inspired bases for LES solution reconstruction in the wall-adjacent cell, the computational framework effortlessly accounts for non-equilibrium effects in high-order codes, with channel flow for proof of concept and periodic hill for validation.
