Article
Mechanics
Xinxian Zhang, Tomoaki Watanabe, Koji Nagata
Summary: In this study, direct numerical simulations of temporally developing turbulent boundary layers were used to investigate the Reynolds number dependence of the turbulent/non-turbulent interface (TNTI) layer. The results revealed the mean thicknesses of the TNTI layer, turbulent sublayer, and viscous superlayer, as well as the characteristics of the irrotational boundary. It was found that the mean shear effects near the TNTI layer are not significant and that the turbulence under the TNTI layer tends to be isotropic at high Reynolds numbers.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Takuya Kawata, Takahiro Tsukahara
Summary: Interscale energy transfers in wall turbulence involve forward transfers representing streak instabilities and reversed transfers representing regeneration of streamwise vortices, as observed in direct numerical simulations.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Matthew A. Subrahmanyam, Brian J. Cantwell, Juan J. Alonso
Summary: This paper introduces a mixing length model for turbulent shear stress in pipe flow and provides a universal velocity profile. The velocity profile accurately approximates both experimental and simulated data in various flow conditions, making it significant for studying the statistical properties of flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jie Yao, Fazle Hussain
Summary: Compressible turbulent plane Couette flows with high Reynolds and Mach numbers were studied through direct numerical simulation. Various turbulence statistics were compared with incompressible flows. The skin friction coefficient decreases with Reynolds number but weakly depends on Mach number. The thermodynamic properties show significant variations with Mach number. Proper scaling transformations collapse the mean velocity profiles for compressible and incompressible cases well. Semilocal units yield a better collapse for Reynolds stress profiles compared to wall units. The length scale of near-wall coherent structures and the strength of the superstructures increase with Reynolds number. The streamwise coherence of the superstructures degrades with increasing Mach number.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
C. Chen, L. He
Summary: Recent findings on wall-bounded turbulence have led to the development of a new modelling method to capture the influence of large-scale coherent structures and scale-interaction on near-wall turbulence. This paper presents a two-scale approach to simulate this influence and validates its effectiveness.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Nikolay Nikitin, Boris Krasnopolsky
Summary: A numerical investigation of turbulent flows in straight pipes with a circular sector cross-section is conducted, focusing on the cases with a convex external corner. It is found that the wall shear stress exhibits singularity at alpha > pi, which persists in turbulent flows. Secondary flows in the vicinity of the external corner are observed and attributed to the centrifugal force arising from fluctuating flow over the corner in the transverse plane. Linear stability analysis supports the hypothesis that the fluctuations are caused by the linear instability of the mean flow field.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Zisong Zhou, Chun-Xiao Xu, Javier Jimenez
Summary: The study found that the large-scale motions in the outer region of wall-bounded flows have a top-down influence on the spanwise motion of near-wall streaks. However, the density of streaks is weakly related to LSMs. Numerical experiments also showed that near-wall streaks merging is not strongly correlated with the generation of LSMs.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Xue Chen, Yongmann M. M. Chung, Minping Wan
Summary: The statistical characteristics and evolution of backflow structures in wall-bounded flows at Reynolds numbers up to R-et=1000 are explored. Backflow is induced through the merging of large-scale high- and low-speed structures near the wall, and is formed at the tail tip of the low-speed structure. The density and area of backflow structures increase with Reynolds number. The average lifespan of backflow structures is 8 wall units, slightly longer in pipes than channels, and they are convected downstream at an average velocity of approximately 10 wall units, similar to Cardesa et al. (J. Fluid Mech., vol. 880, 2019, R3). Backflow structures can occasionally split, merge, and detach from the wall. Evidence suggests that these phenomena are caused by near-wall structures. Split backflow structures are typically larger and more elongated spanwise due to the shearing of near-wall streaks. Wall-detached backflow structures form when the trailing end of the carrier low-speed structure sits on near-wall high-speed streaks. These structures tend to become wall-attached by approaching the wall, following a similar life cycle as normal backflow structures.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Christoph Wenzel, Tobias Gibis, Markus Kloker, Ulrich Rist
Summary: This study quantitatively evaluates the Reynolds analogy factor for self-similar turbulent boundary layers with pressure gradients using direct numerical simulation. The factor is found to increase for adverse-pressure-gradient cases and decrease for favourable-pressure-gradient cases. Mach number has a small influence, and no dependency on Reynolds number was observed. The effects of pressure gradients can be approximated by an analytical relation derived by So in incompressible flow.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
K. Matsuno, S. K. Lele
Summary: The study reveals that at high Mach numbers, the spatial scales of eddying motions in mixing layers progressively decrease, forming independent layers of eddying motions, thereby reducing the effective velocity scale for turbulent motions and suppressing Reynolds stresses, turbulent kinetic energy production and dissipation, and the growth rate of mixing-layer thickness.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Mustafa Z. Yousif, Meng Zhang, Linqi Yu, Ricardo Vinuesa, HeeChang Lim
Summary: This study proposes a new deep-learning-based method for generating turbulent inflow conditions in spatially developing turbulent boundary layer (TBL) simulations. The model combines a transformer and a multiscale-enhanced super-resolution generative adversarial network to predict velocity fields of the TBL at different planes. The model shows remarkable accuracy in predicting velocity fields and reproducing turbulence statistics. Furthermore, it demonstrates the effectiveness of using transformer-based models and generative adversarial networks for various turbulence-related problems.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Mostafa Aghaei-Jouybari, Junlin Yuan, Zhaorui Li, Giles J. Brereton, Farhad A. Jaberi
Summary: Direct numerical simulations were used to investigate the effects of roughness on supersonic turbulent channel flows. Results show that the turbulence is strongly influenced by the roughness topography and the associated shock patterns. Two-dimensional (2-D) roughness generates strong oblique shock waves, while three-dimensional (3-D) roughness results in weaker shocklets. The impingement of shocks on the wall leads to localized augmentations of turbulence shear production. The entropy generation and temperature values are higher in 2-D roughness cases compared to 3-D ones. The effects of roughness extend beyond the near-wall layer due to the presence of shocks.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
J. Guo, X. I. A. Yang, M. Ihme
Summary: Enhanced fluctuations, steep gradients, and intensified heat transfer are characteristic of wall-bounded turbulence at transcritical conditions. This study addresses the poorly understood structure of the thermal boundary layer under realistic density gradients and heating conditions in such flows. By performing direct numerical simulations, an improved mean temperature transformation is proposed to accurately describe the temperature field in transcritical turbulence, providing a framework for the development of models for wall-bounded transcritical turbulence.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Michele Cogo, Francesco Salvadore, Francesco Picano, Matteo Bernardini
Summary: The structure of high-speed zero-pressure-gradient turbulent boundary layers was studied using direct numerical simulation of the Navier-Stokes equations up to high Reynolds numbers, revealing the consequences in supersonic and hypersonic conditions. Instantaneous fields showed elongated strips of uniform velocity and temperature with clear associations between different streaks.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Xiaoning Wang, Jianchun Wang, Shiyi Chen
Summary: This study investigates the effects of compressibility on the statistics and coherent structures of a temporally developing mixing layer through numerical simulations. The results show that as the convective Mach number increases, the streamwise dissipation becomes more effective in suppressing turbulent kinetic energy. At low convective Mach numbers, the mixing layer is accompanied by spanwise Kelvin-Helmholtz rollers, while at higher convective Mach numbers, large-scale high- and low-speed structures dominate. The study also reveals a correlation between high-shearing motions on top of low-speed structures and the clustering of small-scale vortical structures.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Min Yoon, Jinyul Hwang, Hyung Jin Sung
JOURNAL OF FLUID MECHANICS
(2018)
Article
Computer Science, Interdisciplinary Applications
Jin Lee, Tamer A. Zaki
COMPUTERS & FLUIDS
(2018)
Article
Mechanics
Jinyul Hwang, Hyung Jin Sung
JOURNAL OF FLUID MECHANICS
(2018)
Article
Physics, Fluids & Plasmas
Zhao Wu, Jin Lee, Charles Meneveau, Tamer Zaki
PHYSICAL REVIEW FLUIDS
(2019)
Article
Physics, Fluids & Plasmas
Jongmin Yang, Jinyul Hwang, Hyung Jin Sung
PHYSICAL REVIEW FLUIDS
(2019)
Article
Mechanics
Min Yoon, Jinyul Hwang, Jongmin Yang, Hyung Jin Sung
JOURNAL OF FLUID MECHANICS
(2020)
Article
Physics, Fluids & Plasmas
X. I. A. Yang, Z-H Xia, J. Lee, Y. Lv, J. Yuan
PHYSICAL REVIEW FLUIDS
(2020)
Article
Mechanics
Oh-Kyoung Kwon, Jin Lee, Junghoon Lee, Ji-Hoon Kang, Jung-Il Choi
INTERNATIONAL JOURNAL OF COMPUTATIONAL FLUID DYNAMICS
(2020)
Article
Mechanics
Jinyul Hwang, Jae Hwa Lee, Hyung Jin Sung
JOURNAL OF FLUID MECHANICS
(2020)
Article
Mechanics
Mohammad Javad Sayyari, Jinyul Hwang, Kyung Chun Kim
Summary: This study examines the capability of an unsupervised deep learning network to capture large-scale structures in a fully developed turbulent channel flow. The results demonstrate that the generative adversarial network accurately presents statistical data and successfully predicts structural characteristics hidden in the training dataset. Additionally, the study finds that larger-scale structures exhibit more aggressive waviness behavior, leading to an increase in the number of vortical structures surrounding low-momentum 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)
Proceedings Paper
Energy & Fuels
Jinyul Hwang, Hyung Jin Sung
PROGRESS IN TURBULENCE VIII
(2019)
Article
Mechanics
Juhyung Han, Jinyul Hwang, Min Yoon, Junsun Ahn, Hyung Jin Sung
Article
Mechanics
Jinyul Hwang, Hyung Jin Sung
Article
Mechanics
Jin Lee, Hyung Jin Sung, Tamer A. Zaki
JOURNAL OF FLUID MECHANICS
(2017)