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
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
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
Yukio Kaneda, Yoshinobu Yamamoto
Summary: This paper extends Kolmogorov's local similarity hypotheses to include the influence of mean shear on the statistics of fluctuating velocity. The moments of the velocity gradients are determined by the local turbulent energy dissipation rate, kinematic viscosity, and parameter gamma. The anisotropy of moments decreases approximately in proportion to gamma when gamma is small in an appropriate sense.
JOURNAL OF FLUID MECHANICS
(2021)
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
Jiho You, David A. Buchta, Tamer A. Zaki
Summary: Direct numerical simulations were conducted to investigate turbulent boundary layers over a concave wall with and without free-stream turbulence. The presence of free-stream turbulence reduced reverse flow probability, increased skin friction, and promoted the amplification of Gortler structures. Additionally, coherent roll motions in the forced flow facilitated mixing of free-stream and boundary-layer fluids.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jonathan Neuhauser, Kay Schaefer, Davide Gatti, Bettina Frohnapfel
Summary: Heterogeneous roughness in the form of streamwise aligned strips can generate large scale secondary motions under turbulent flow conditions. We propose a simple roughness model that can capture the features of turbulent secondary flow without impacting the laminar base flow. The model shows good agreement with experimental data in terms of the secondary flow topology.
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
Alessandro Ceci, Andrea Palumbo, Johan Larsson, Sergio Pirozzoli
Summary: This study investigates the influence of turbulence inflow generation on high-speed turbulent boundary layers through direct numerical simulations (DNS). Two main types of inflow conditions are considered and compared. DNS with very long streamwise domains are performed to provide reliable data. Simulations with shorter domains are then conducted and compared with benchmark data, revealing significant deviations and dependency on inflow turbulence seeding.
THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS
(2022)
Article
Thermodynamics
L. Laguarda, S. Hickel, F. F. J. Schrijer, B. W. van Oudheusden
Summary: Wall-resolved large-eddy simulations were used to investigate the Reynolds number effects in supersonic turbulent boundary layers at Mach 2.0. The study covered a wide range of friction Reynolds numbers and identified trends in various statistics and scaling laws. The size and topology of turbulent structures in the boundary layer were examined, with a focus on the outer-layer motions at high Reynolds numbers. The study also assessed the influence of outer-layer structures on near-wall turbulence and the sensitivity of uniform momentum regions to compressibility.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Mechanics
Mengze Wang, Tamer A. Zaki
Summary: Estimation of the initial state of turbulent channel flow from limited data is investigated using an adjoint-variational approach. The study demonstrates the robustness of the algorithm to observation noise and evaluates the impact of the spatiotemporal density of the data on estimation quality. Results show a resolution threshold for successful reconstruction and highlight the difficulty of reconstructing wall-detached motions from wall data.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
J. C. Klewicki
Summary: High resolution direct numerical simulation data are used to investigate the similarity solutions for mean velocity and Reynolds shear stress in turbulent channel flow. The analysis yields an invariant form of the mean momentum equation valid over a significant portion of the flow domain. The results provide insights into the development of wall-flow models and support conjectures regarding the behavior of similarity parameters at large Reynolds numbers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Automation & Control Systems
Donggun Son, Haecheon Choi
IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY
(2019)
Article
Computer Science, Interdisciplinary Applications
Woojin Kim, Haecheon Choi
COMPUTERS & FLUIDS
(2019)
Review
Thermodynamics
Woojin Kim, Haecheon Choi
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2019)
Article
Engineering, Mechanical
Hongkwon Lee, Keuntae Park, Haecheon Choi
JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY
(2019)
Article
Biophysics
Woojin Kim, Hansol Lee, Jungil Lee, Daehan Jung, Haecheon Choi
JOURNAL OF BIOMECHANICS
(2019)
Article
Mechanics
Sehyeong Oh, Boogeon Lee, Hyungmin Park, Haecheon Choi, Sun-Tae Kim
JOURNAL OF FLUID MECHANICS
(2020)
Article
Engineering, Mechanical
Boogeon Lee, Sehyeong Oh, Haecheon Choi, Hyungmin Park
JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY
(2020)
Article
Engineering, Mechanical
Dongri Kim, Hyungrok Do, Haecheon Choi
EXPERIMENTS IN FLUIDS
(2020)
Article
Multidisciplinary Sciences
Woojin Kim, Haecheon Choi, Jihoon Kweon, Dong Hyun Yang, Young-Hak Kim
Article
Mechanics
Jonghwan Park, Haecheon Choi
JOURNAL OF FLUID MECHANICS
(2020)
Article
Mechanics
Jonghwan Park, Haecheon Choi
Summary: The study developed a subgrid-scale model using a fully connected neural network and conducted both a priori and a posteriori tests to evaluate its prediction performance. Results showed that while the NN-based SGS model can provide good predictions under certain conditions, it also exhibited stability issues in some cases.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Dohyun Jin, Zhi Wu, Haecheon Choi
Summary: This study proposes a predictive model for the drag coefficient of a circular cylinder based on the mean streamwise velocity and Reynolds normal stresses in the wake, which shows good agreement with numerical simulations across various Reynolds numbers.
Article
Mechanics
Zhi Wu, Haecheon Choi
Summary: Steady discrete blowing is more effective for drag reduction than steady uniform blowing, with a maximum drag reduction of 38%. Time-periodic uniform blowing is more effective than steady discrete blowing, with maximum drag reduction of 68%. Different vortex lock-on phenomena play a significant role in drag decrease and increase during time-periodic blowing.
Article
Mechanics
Daeun Song, Woojin Kim, Oh-Kyoung Kwon, Haecheon Choi
Summary: We conducted a direct numerical simulation of the flow over the Tacoma Narrows Bridge to reproduce the vertical and torsional vibrations that occurred before its collapse in 1940. The simulation used real-scale structural parameters and modified the fluid property to provide realistic aerodynamic force and moment. Through the simulation, we observed vertical vibration resulting from vortex shedding frequency lock-in, followed by exponential growth of torsional vibration due to aeroelastic fluttering. We also investigated the roles of free-stream velocity and vertical vibration in the growth of torsional vibration.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Sangwoo Ahnn, Haecheon Choi
Summary: Numerical analysis is conducted to investigate the aerodynamic performance and characteristics of flow around a simplified vertical-axis wind turbine (VAWT). The primary flow feature observed is the formation and evolution of leading-edge vortices (LEVs) at lower tip-speed ratios, which have a notable impact on the power coefficient. A modified tip-speed ratio allows for the representation of flow structures with different tip-speed ratios and number of blades. The time-averaged power coefficient is a function of the modified tip-speed ratio, and its maximum value occurs at a specific range of the modified tip-speed ratio.