Article
Mechanics
Ioannis K. Kaminaris, Elias Balaras, Michael P. Schultz, Ralph J. Volino
Summary: This study investigates the evolution of turbulent boundary layers over truncated cones in both staggered and random configurations using direct numerical simulations. The computational results are validated using experimental measurements and show a good agreement. The presence of secondary flows in the cross-stream plane is observed in both staggered and random arrangements, with the momentum pathways approaching the edge of the boundary layer in random arrangements. The correlation between the momentum pathways and the leading edge of the roughness is clear, while the correlation to the local topography is weak.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
D. D. Wangsawijaya, N. Hutchins
Summary: This study examines the turbulent boundary layers developing over surfaces with spanwise heterogeneous roughness. It finds that the heterogeneous cases induce counter-rotating secondary flows, which are compared to the large-scale turbulent structures over smooth walls. The results suggest that the secondary flows are spanwise-locked turbulent structures, with the strength of the structures and locking efficacy determined by the roughness half-wavelength. The study also finds that the secondary flows exhibit maximum unsteadiness when the roughness half-wavelength is approximately 1.
JOURNAL OF FLUID MECHANICS
(2022)
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
Shivsai Ajit Dixit, Abhishek Gupta, Harish Choudhary, Thara Prabhakaran
Summary: This study derives a dynamically consistent scaling of mean skin friction in zero-pressure-gradient turbulent boundary layers and fully developed pipe and channel flows. The results show that a universal power scaling law is applicable, but the semi-empirical finite-skin friction model fails to universally describe all flows. This non-universality can be explained by considering the differences in flow boundary conditions and geometry, which affect the outer-layer structures. An empirical correction based on the shape factor is proposed, and it is shown to collapse the data from all flows onto a single universal curve.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Marco Ferro, Bengt E. G. Fallenius, Jens H. M. Fransson
Summary: New experimental results demonstrate that turbulent asymptotic suction boundary layers (TASBLs) can be achieved with wall suction, showing unique characteristics independent of streamwise location. The wall suction results in a significant damping of velocity fluctuations and reduces turbulent activity.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Matthew Bross, Sven Scharnowski, Christian J. Kaehler
Summary: Studies have shown that in compressible turbulent boundary layer flows, the frequencies of superstructures have slightly longer streamwise wavelengths, and there is a distinct increase in the spanwise spacing of superstructures in supersonic cases compared to subsonic and transonic turbulent boundary layers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
R. Baidya, J. Philip, N. Hutchins, J. P. Monty, I. Marusic
Summary: The study reveals that the impact of Reynolds number on spanwise velocity generally follows a logarithmic trend, with the presence of intermediate-scale eddies leading to characteristics related to the distance from the wall.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
M. Gul, B. Ganapathisubramani
Summary: This study investigates the flow characteristics of a turbulent boundary layer over different sand-grain roughness created by different sandpapers. The results show self-similarity in flow properties within a certain range, regardless of transitional or fully rough conditions. Despite differences in turbulence profiles, large-scale structures across all locations remain independent of roughness parameters.
JOURNAL OF FLUID MECHANICS
(2021)
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
Michael Heisel, Charitha M. de Silva, Nicholas Hutchins, Ivan Marusic, Michele Guala
Summary: The statistical properties of prograde spanwise vortex cores and internal shear layers in high-Reynolds-number turbulent boundary layers are evaluated. Results show the importance of the local large-eddy turnover time in determining the strain rate confining the size of the vortex cores and shear layers. The study highlights the relevance of the turnover time and the Taylor microscale in explaining the interaction of coherent velocity structures in the boundary layer flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
C. Chan, P. Schlatter, R. C. Chin
Summary: The flow physics of turbulent boundary layers was investigated using spectral analysis based on the spanwise scale decomposition of the Reynolds stress transport equation with data obtained from direct numerical simulation. The study revealed evidence of inverse turbulent kinetic energy transfer occurring in the near-wall region, as well as inverse transfer of Reynolds shear stress transport across the entire boundary layer. Interactions between large-scale structures and the free stream flow were also observed at the edge of the boundary layer.
JOURNAL OF FLUID MECHANICS
(2021)
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
Christopher J. Howland, Chong Shen Ng, Roberto Verzicco, Detlef Lohse
Summary: The study investigates convective and turbulent boundary layers on a vertical surface using numerical simulations. It finds that within a certain parameter range, the flow is consistent with a 'buoyancy-controlled' regime and the heat flux scales linearly with the friction velocity.
JOURNAL OF FLUID MECHANICS
(2021)
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
Cheng Cheng, Wei Shyy, Lin Fu
Summary: A new methodology was developed to assess the distribution of wall-attached eddies, revealing that the SIAs depend on the Reynolds number at low and medium Reynolds numbers, saturating at 45 degrees as the Reynolds number increases. The average SIA reported in previous experimental studies was shown to be the result of the additive effect of multi-scale attached eddies.
JOURNAL OF FLUID MECHANICS
(2022)
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.