Article
Energy & Fuels
Umair Ismail
Summary: Using direct numerical simulation, this study investigates the transition of a turbulent boundary layer as it encounters a smooth-to-rough step change. The results show the development of a self-preserving state and the emergence of an equilibrium layer. The statistics inside the inner layer adapt earlier than the outer layer, and the roughness characteristics are different from the rough-to-smooth transition scenarios. The study also reveals the effects of the underlying rough surface on the flow characteristics.
Article
Mechanics
Zhigang Zhang, Fulin Tong, Junyi Duan, Xinliang Li
Summary: This study conducted a direct numerical simulation of an incident shock wave impinging on a 12° supersonic turbulent expansion corner at a 33.2° angle, revealing the significant influence of expansion on the physics of interaction. The expansion led to reduced wall pressure and separation bubble size, affecting the motion induced by the shock. The study also analyzed the evolution of the reattached boundary layer and the generation mechanism of skin friction.
Article
Engineering, Multidisciplinary
Witold Elsner, Artur Drozdz, Ewa Szymanek, Artur Tyliszczak, Pawel Niegodajew
Summary: The effects of surface roughness and pressure gradient on turbulent boundary layer development were investigated in this study. The results showed that higher amplitude of the 2D wavy surface increased turbulence production and led to earlier separation of the TBL. In contrast, the 3D topography resulted in a greater streamwise velocity deficit, lower growth of velocity fluctuations, and smaller and less energetic structures downstream of the corrugation compared to the 2D case.
APPLIED MATHEMATICAL MODELLING
(2022)
Article
Mechanics
Rong Ma, Karim Alame, Krishnan Mahesh
Summary: The numerical simulation reveals that the influence of a rough bottom wall on flow mainly manifests in the roll-up of the shear layer in the wall-normal direction. There is a strong correlation between the height of random short wave roughness and wall shear stress, depending on the local roughness topography.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Xiao-Ping Chen, Deng-Song Huang, Shuo Zhao, Chen-Shao Zhu
Summary: This study conducts direct numerical simulations to investigate the influence of compressibility effects on turbulent statistics and large-scale structures in temporally evolving turbulent channel flows with a weak spanwise rotation. The results show that compressibility has some impact on the turbulent statistics distributions, but many asymmetric characteristics still exist.
Article
Mechanics
Jie Yao, Saleh Rezaeiravesh, Philipp Schlatter, Fazle Hussain
Summary: This study conducted direct numerical simulations of flow in a smooth circular pipe and obtained various turbulence statistics. A comparison with other simulations and experiments revealed small but noticeable differences. The friction factor deviated from the Prandtl friction law at low and high Reynolds numbers. The wall shear stress fluctuations and axial turbulence intensity in the pipe were lower than in the channel, but the difference decreased with increasing Reynolds number.
JOURNAL OF FLUID MECHANICS
(2023)
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
Energy & Fuels
Feng Ji, Jing Ding, Jianfeng Lu, Weilong Wang
Summary: Direct numerical simulations were conducted to investigate spatially developing thermal turbulent boundary layers over angle-ribbed walls. The results revealed that ribs with a 45 degrees angle exhibited the highest drag coefficient, while ribs with a 30 degrees angle showed the greatest improvement in Stanton number. The study also found that the V-shaped rib cases had significantly increased streamwise velocity and dimensionless temperature near the wall, which were attenuated by secondary flows further away from the ribs. Furthermore, the enhancement in heat transfer efficiency in the 30 degrees rib cases was mainly attributed to the large dispersive heat flux.
Article
Mechanics
Riccardo Balin, K. E. Jansen
Summary: Direct numerical simulation shows that the strong favorable pressure gradient on the bump causes the boundary layer to enter a relaminarization process, significantly weakening near-wall turbulence. However, at the bump peak, when the favorable pressure gradient switches to an adverse gradient, near-wall turbulence is suddenly enhanced through a partial retransition process.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Aerospace
Qiang Liu, Zhenbing Luo, Lin Wang, Guohua Tu, Xiong Deng, Yan Zhou
Summary: Direct numerical simulations were conducted on a spatially developing Ma 2.25 supersonic turbulent boundary layer with streamwise-striped wall blowing for turbulence drag reduction. It was found that despite weak control amplitudes, SSB can result in drag reduction effects. Analysis using compressible Renard-Deck decomposition revealed that the spatial growth term is mainly responsible for turbulence drag reduction.
AEROSPACE SCIENCE AND TECHNOLOGY
(2021)
Article
Engineering, Aerospace
Fulin Tong, Dong Sun, Xinliang Li
Summary: The study investigates the interaction of a 30-degree oblique shock wave with a supersonic turbulent boundary layer at Ma (infinity) = 2.9 and Re-0 = 2400 over a wavy-wall, revealing significant influences of the wavy-wall on flow field characteristics, skin-friction, pressure, and turbulence kinetic energy budget, leading to an increase in separation region and the formation of bubbles.
CHINESE JOURNAL OF AERONAUTICS
(2021)
Article
Meteorology & Atmospheric Sciences
Soumak Bhattacharjee, Evgeny Mortikov, Andrey Debolskiy, Evgeny Kadantsev, Rahul Pandit, Timo Vesala, Ganapati Sahoo
Summary: This study investigates the characteristics of turbulent flow in a closed channel with a canopy and compares the effects of different drag models on the flow. The results show that the drag formulations significantly influence the mean and turbulent profiles near the canopy. The presence of the canopy also leads to changes in the local anisotropy of the turbulent flow.
BOUNDARY-LAYER METEOROLOGY
(2022)
Article
Mechanics
J. M. F. Peter, M. J. Kloker
Summary: This article introduces the research on film cooling technology for the nozzle extension of rocket engines. By conducting basic experiments and numerical simulations, several new influencing factors have been identified, which are of great guidance for improving cooling modeling and simulation.
Article
Mechanics
Dongdong Xu, Xuesong Wu
Summary: This study investigates how free-stream vortical disturbances with sufficiently long wavelength can prevent separation in a two-dimensional boundary layer, numerical results show that strong nonlinear mean-flow distortion associated with nonlinear streaks or Gortler vortices can eliminate separation, and the critical FSVD intensity, epsilon(c), depends on streamwise curvature, pressure gradient, and frequency of FSVD, with concave curvature inhibiting separation and stronger adverse pressure gradient requiring higher epsilon(c) to prevent separation. Interestingly, unsteady FSVD with low frequencies are more effective than steady ones in suppressing separation.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
S. Mahmoodi-Jezeh, Bing-Chen Wang
Summary: This study investigates the impact of inclined or V-shaped ribs on turbulent flow in a square duct, revealing significant differences in flow physics between the two ribbed duct cases. The research analyzes the near-wall turbulence structures and momentum transfer, highlighting the sensitivity of turbulence field to rib geometry and boundary layers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jongmin Yang, Yujia Chen, Jun-Duo Zhang, Wei-Xi Huang, Hyung Jin Sung
Summary: The study on the hydrodynamics of tuna caudal keels shows that they can increase the average cruising speed and thrust.
Article
Mechanics
Hae Nyeok Kim, Seung Joong Kim, Woorak Choi, Hyung Jin Sung, Sang Joon Lee
Summary: This study experimentally investigated the shear flow-induced depletion of lubricant impregnated in a single cavity, revealing that a large-scale vortex near the lubricant meniscus dramatically slows down the depletion rate. It was also found that in biomimetic LIS, cavities with smaller opening ratio have better sustainability and less lubricant depletion. These findings provide valuable insights for the design of a robust LIS system for effective and sustainable drag reduction.
Article
Mechanics
Qian Mao, Jiazhen Zhao, Yingzheng Liu, Hyung Jin Sung
Summary: The hydrodynamic benefits of fixed and flapping pectoral fins were explored using the penalty immersed boundary method. It was found that the vortices generated by the pectoral fins increase the pressure difference between the upper and lower sides of the plate, resulting in an enhancement of both the cruising speed and thrust. Horizontal flapping pectoral fins with low flapping frequency enhance the propulsive efficiency. Flexible flapping fins enhance the cruising speed. Additionally, the presence of one flapping fin on one side of the flexible plate induces asymmetrical heaving of the plate and increases the lateral forces, which might help fish achieve turning and maintain balance in perturbed flows.
Article
Mechanics
Jiazhen Zhao, Qian Mao, Guang Pan, QiaoGao Huang, Hyung Jin Sung
Summary: The hydrodynamics of a self-propelled flexible plate near the ground were investigated. The interaction between the plate and the ground generates a strong vortex, leading to an increase in cruising speed. The aspect ratio and gap distance from the ground also play a role in determining the performance of the plate.
Letter
Mechanics
Guo-Zhen Ma, Chun-Xiao Xu, Hyung Jin Sung, Wei-Xi Huang
Summary: This paper proposes a roughness scaling method based on the direct numerical simulation of turbulent channel flow over three-dimensional sinusoidal rough walls in a transitionally rough regime. A new coupling scale is defined and the relationships between various parameters are explored.
Article
Mechanics
Qian Mao, Jiazhen Zhao, Yingzheng Liu, Hyung Jin Sung
Summary: The hydrodynamic mechanism of drag reduction by a rotationally oscillating cylinder with a flexible filament was explored using the penalty immersed boundary method. The study found that drag reduction is achieved through different mechanisms depending on the oscillation mode.
Article
Chemistry, Multidisciplinary
Seunggyu Kim, Hyeono Nam, Beomseok Cha, Jinsoo Park, Hyung Jin Sung, Jessie S. Jeon
Summary: The cytotoxic response of natural killer (NK) cells in a microreactor to surface acoustic waves (SAWs) is investigated. Results show that SAWs do not damage suspended NK cells, and can increase intracellular Ca2+ concentrations and enhance cell-mediated cytotoxicity.
Article
Engineering, Multidisciplinary
Jun-Duo Zhang, Hyung Jin Sung, Wei-Xi Huang
Summary: In this study, the hydrodynamic interaction between the large crescent dorsal fin and caudal fin in tuna was numerically explored. The presence of the dorsal fin substantially enhanced the thrust on the caudal fin, and a constructive interaction between the leading-edge vortex on the caudal fin and the vortices shed from the dorsal fin was identified. The flapping phase of the caudal fin and the Strouhal number had an influence on the dorsal fin-caudal fin interaction, while the Reynolds number did not have a substantial effect.
BIOINSPIRATION & BIOMIMETICS
(2022)
Article
Mechanics
Qian Mao, Jiazhen Zhao, Yingzheng Liu, Hyung Jin Sung
Summary: This study investigates the hydrodynamic mechanism of drag reduction by a flexible hairy coating through simulations and experimental data comparison, revealing the importance of flexible hairy coatings in drag reduction and the effects of different parts of the coating on drag reduction.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Min Yoon, Hyung Jin Sung
Summary: This study explores wall-attached structures in a drag-reduced turbulent channel flow and examines their influence on drag reduction. The results show that the population density of wall-attached structures decreases and the friction density reduces with streamwise slip, leading to an overall drag reduction.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Qian Mao, Yingzheng Liu, Hyung Jin Sung
Summary: This study investigated the hydrodynamic mechanism of drag reduction by flapping a flexible filament behind a stationary cylinder using the penalty immersed boundary method. The effects of filament parameters on drag reduction were examined, and three distinct flapping modes were observed. The oscillation and undulation modes were found to be more beneficial for drag reduction than the vortex-dominated mode.
Article
Mechanics
Qian Mao, Yingzheng Liu, Hyung Jin Sung
Summary: The hydrodynamic mechanism of drag reduction by flapping flexible filaments behind a cylinder was investigated using the penalty immersed boundary method. The effects of phase difference, attachment height, and flapping amplitude on drag reduction were studied. Flapping filaments weaken vortex shedding through destructive interaction, with out-of-phase filaments showing better drag reduction than in-phase filaments. Minimum drag is achieved at appropriate attachment height and flapping amplitude to avoid filament collision and weaken shear-layer-filament interaction. The clapping filaments are more effective than snaking filaments. The total drag decreases with increasing Reynolds number, transitioning from 2S mode to P + S mode wake pattern.
Article
Mechanics
Guo-Zhen Ma, Chun-Xiao Xu, Hyung Jin Sung, Wei-Xi Huang
Summary: Direct numerical simulations (DNSs) were conducted to investigate the effects of roughness on statistical properties and large-scale coherent structures in turbulent channel flow over three-dimensional sinusoidal rough walls. The study examined the similarities in mean streamwise velocity and Reynolds stresses in the outer layer by varying the roughness Reynolds number and the ratio of roughness height to the half-channel height. Spectral analysis and scale-energy path display were used to explore the energy transfer mechanism of turbulent motions with different sized roughness elements. The results showed that increasing roughness Reynolds number led to a downward shift of the mean velocity profile and decreased intensity of turbulent Reynolds stresses.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Qian Mao, Yingzheng Liu, Hyung Jin Sung
Summary: The flow-induced snap-through dynamics of a buckled flexible filament were studied by using the penalty immersed boundary method. The effects of filament length, bending rigidity, and Reynolds number on the mode transition were systematically investigated. Three different modes were observed when these parameters were varied: equilibrium mode, streamwise oscillation mode, and snap-through oscillation mode. The increase in transverse fluid force induced the snap-through oscillation mode, while a vortex-induced vibration and a self-excited vibration occurred in the streamwise oscillation mode and snap-through oscillation mode respectively.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Biochemical Research Methods
Hyeono Nam, Jong-Eun Park, Waqas Waheed, Anas Alazzam, Hyung Jin Sung, Jessie S. Jeon
Summary: Traveling surface acoustic waves (SAWs) were used for the lysis of cancer cells without any chemical reagents, followed by Raman spectrum profiling to explore detailed cell-derived data. Mechanical cell lysis was achieved using polystyrene microparticles (PSMPs) and the Raman signals from the lysed cells were enhanced by gold nanoparticles (AuNPs) through nanogaps formed by the AuNPs. The lysis efficiency was evaluated by varying the size and concentration of the PSMPs.
Article
Thermodynamics
Navid Freidoonimehr, Azadeh Jafari, Maziar Arjomandi
Summary: In this study, a high-fidelity flow visualisation technique is used to investigate the resemblance between a turbulent boundary layer generated by different tripping devices in a lab environment and a naturally developed canonical turbulent boundary layer. The study finds that the blockage created by trips is the main factor affecting the turbulence statistics at a certain downstream distance.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
Yuning Wang, Alberto Solera-Rico, Carlos Sanmiguel Vila, Ricardo Vinuesa
Summary: This study proposes a method that combines 6-VAEs for modal decomposition and transformer neural networks for temporal-dynamics prediction in the latent space to develop reduced-order models (ROMs) for turbulent flows. The method achieves high reconstruction accuracy and accurate prediction of temporal dynamics.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
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
Thermodynamics
A. Doehring, T. Kaller, S. J. Schmidt, N. A. Adams
Summary: In this study, well-resolved large-eddy simulations were used to investigate turbulent duct flows with a square cross section. The influence of a modified wall shear stress on the secondary flow was analyzed by artificially modifying the wall shear stress at one of the four walls. The results showed that the modification led to an asymmetrical distribution of the secondary flow source terms, affecting the momentum distribution. Furthermore, the anisotropy of the Reynolds stress tensor, which induces the secondary flow vortices, was significantly affected by the wall shear stress modulation.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)