Article
Energy & Fuels
Hoai Thanh Nguyen, Kyoungsik Chang, Sang-Wook Lee, Jaiyoung Ryu, Minjae Kim
Summary: In this study, the effect of parameters on drag-reducing performance of superhydrophobic surfaces was investigated using direct numerical simulation (DNS). The results reveal the drag reduction mechanism through turbulent kinetic energy budget and observation of coherent structures. The study demonstrates that significant drag reduction can be achieved under specific solid fraction and distribution conditions.
Article
Mechanics
Wen-Hua Zhang, Qian-Qian Shao, Yu-Ke Li, Yu Ma, Hong-Na Zhang, Feng-Chen Li
Summary: The study conducted DNS of EIT using the Oldroyd-B model for the first time, revealing the complex energy transformations involved in EIT and confirming the formation of sheet-like structures reflecting polymer extension characteristics.
Article
Mechanics
Pritam Giri, Ratnesh K. Shukla
Summary: We analyze the transport behavior of surface-actuated spheroidal microswimmers and find that tangential and wall-normal surface actuations enable transport at minimal energetic cost. The propulsive performance of a forced spheroidal swimmer is higher than that of a self-propelled swimmer, and the optimal energy expenditure for forced transport is passive overall. The combination of external forcing and optimal surface actuation can substantially enhance the transport of streamlined and bluff microswimmers.
Article
Engineering, Chemical
Gizem Ozler, Mustafa Demircioglu, Holger Grosshans
Summary: In CFD simulations of two-phase flows, accurate drag force modeling is essential for predicting particle dynamics. However, a generally valid formulation is lacking, as all available drag force correlations have been established for specific flow situations. This paper reports the effect of drag force modeling on the flow of electrically charged particles.
ADVANCED POWDER TECHNOLOGY
(2023)
Article
Mechanics
Xu Liu, Hongbo Zhu, Yan Bao, Dai Zhou, Zhaolong Han
Summary: In this study, direct numerical simulations are conducted to investigate the control method of turbulent pipe flow under streamwise-varying wall rotation. The results show that increasing the wavelength is a better choice for improving control efficiency than increasing the amplitude. The rotational effect leads to the formation of a spatial Stokes layer, which has different effects on drag reduction depending on its thickness. Furthermore, it is found that achieving turbulence relaminarization requires a sufficient thickness of the Stokes layer and velocity amplitude.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Thermodynamics
Amin Moosaie, Hamed Panahi-Kalus
Summary: The study focuses on fully developed turbulent flow and heat transfer in a plane channel with different velocity slip and no-slip conditions. It is found that velocity and temperature fluctuations behave differently, with temperature jump leading to reduced turbulent heat flux under velocity slip condition, enhancing heat transfer.
JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER
(2021)
Article
Thermodynamics
Alexandros I. Iatridis, Ioannis E. Sarris, Nicholas S. Vlachos
Summary: Toroidal magnetohydrodynamic flows are crucial for fusion technology, and the effect of toroidal square duct radius on flow transition is numerically studied. The transition occurs in different Ha number regimes, regardless of the toroidal duct mean radius.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2021)
Article
Mechanics
Yuehao Sun, Ze-Rui Peng, Dan Yang, Yongliang Xiong, Lei Wang, Lin Wang
Summary: This article investigates the dynamics of a two-dimensional flow over a rigid flat plate with a trailing closed flexible filament acting as a deformable afterbody. Numerical methods are used to study the flow patterns and dynamics of the rigid-flexible coupling system and to explore the effects of Reynolds number and length ratio. The study identifies five typical state modes based on the filament shape and dynamics and demonstrates the significant drag reduction achieved by utilizing the flexible filament.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Rafsan Rabbi, Nathan B. Speirs, Akihito Kiyama, Jesse Belden, Tadd T. Truscott
Summary: The study shows that throwing another object in front of a free-falling object impacting onto water surface can reduce the impact force in some cases, but the effect varies under different conditions. The formation of cavity by the first object and the timing of impact by the second object are found to influence the impact acceleration on the trailing object.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Acoustics
Elias J. G. Arcondoulis, Thomas F. Geyer, Yu Liu
Summary: The study found that applying Structured Porous Coated Cylinders (SPCCs) to smooth cylinders can reduce noise levels, similar to randomized porous coated cylinders. Altering the porosity in different regions has some influence on high frequency noise.
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA
(2021)
Article
Engineering, Marine
Zhihan Xu, Xu Chang, Haiyang Yu, Wen-Li Chen, Donglai Gao
Summary: In this study, a new passive flow control strategy utilizing 3D printed porous surface was investigated to manipulate the dynamic wake evolution and flow characteristics around a stationary circular cylinder. The presence of the porous surface suppressed vortex shedding and reduced drag, as confirmed by POD analysis, dynamic wake evolution analysis, and power spectrum analysis.
Article
Engineering, Marine
Xi Chen, Marc Perlin
Summary: Skin-friction drag in liquid flows can be reduced by various methods, but they all have drawbacks. To improve drag reduction in turbulent flows, a novel method of perfusing air through a porous medium is investigated and showed promising results in the experiment.
Article
Engineering, Chemical
Haishan Miao, Hao Zhang, Xizhong An, Chunhai Ke, Aibing Yu
Summary: This study investigates the combined effect of particle shape and porosity on the momentum and heat transfer of granular matter under laminar flow. It is found that particle shape, characterized by aspect ratio, plays a dominant role in affecting the drag coefficient and Nusselt number, while the influence of porosity becomes significant under high Reynolds number conditions.
Article
Mechanics
Wonhee Cho, Seongkwang Heo, Sang Joon Lee
Summary: This study proposes a method of surface air injection to enhance the stability of air plastrons on superhydrophobic surfaces and investigates their dynamic behavior using x-ray imaging. The results show that the depletion rate of air plastrons is influenced by the air injection rate, and the stability of plastrons is improved with higher injection rates.
Article
Mechanics
M. Mcdermott, T. A. E. Riou, P. R. Resende, M. C. T. Wilson, A. M. Afonso, G. de Boer
Summary: A novel open-source anisotropic k-epsilon-v(2)-f model is proposed for turbulent viscoelastic duct flow with dilute polymeric solutions. The model incorporates polymeric terms into the governing equations of the turbulence model for channel and square duct flow of Newtonian fluids. The performance of the model is validated by simple closure models and direct numerical simulation data, and it demonstrates good capability in capturing drag reduction features under a wide range of rheological parameters.
Article
Engineering, Mechanical
Davide Gatti, Lars von Deyn, Pourya Forooghi, Bettina Frohnapfel
EXPERIMENTS IN FLUIDS
(2020)
Article
Thermodynamics
Marco Atzori, Ricardo Vinuesa, Georg Fahland, Alexander Stroh, Davide Gatti, Bettina Frohnapfel, Philipp Schlatter
FLOW TURBULENCE AND COMBUSTION
(2020)
Article
Engineering, Mechanical
A. Codrignani, D. Savio, L. Pastewka, B. Frohnapfel, R. van Ostayen
TRIBOLOGY INTERNATIONAL
(2020)
Article
Engineering, Mechanical
R. Leister, A. F. Najafi, D. Gatti, J. Kriegseis, B. Frohnapfel
TRIBOLOGY INTERNATIONAL
(2020)
Article
Mechanics
Tobias Karl, Davide Gatti, Thomas Boehlke, Bettina Frohnapfel
Summary: This work discusses the impact of fiber orientation distribution feedback on base flow and fiber orientation itself during mold filling simulations. Different closure methods are considered for modeling flow-induced anisotropy, with results showing significant differences in fiber orientation between decoupled and coupled methods in different flow scenarios. Viscosity and elasticity tensor exhibit flow-induced anisotropies and are highly dependent on closure and coupling.
Article
Engineering, Aerospace
Georg Fahland, Alexander Stroh, Bettina Frohnapfel, Marco Atzori, Ricardo Vinuesa, Philipp Schlatter, Davide Gatti
Summary: This study focuses on the parametric study of turbulent boundary-layer control on airfoils through uniform blowing or suction, showing the potential benefits of blowing on the pressure side under various conditions and achieving a maximum total net drag saving of 14%. The comprehensive analysis using Reynolds-average Navier-Stokes simulations provides general conclusions and guidelines for future experimental or numerical studies on similar boundary-layer control schemes.
Article
Engineering, Multidisciplinary
Martin Woerner, Nima Samkhaniani, Xuan Cai, Yanchen Wu, Arijit Majumdar, Holger Marschall, Bettina Frohnapfel, Olaf Deutschmann
Summary: This study investigates the interaction between UWS droplets and solid substrates of varying wettability using numerical simulations, identifying a strong influence of substrate wettability on droplet dynamics. The results may be useful for developing more advanced drop-wall interaction models in CFD codes for large-scale computations of UWS sprays.
APPLIED MATHEMATICAL MODELLING
(2021)
Article
Mechanics
Frieder Kaiser, Malte von der Burg, Joel Sommeria, Samuel Viboud, Bettina Frohnapfel, Davide Gatti, David E. Rival, Jochen Kriegseis
Summary: The study investigated the interaction between unsteady vortex-wall of animal propulsion by examining a vorticity-annihilating boundary layer during the spin-down of a vortex from solid-body rotation. The experiment demonstrated that at high Reynolds numbers, the onset of transition occurs earlier, leading to similar rates of vorticity annihilation in the early stages of spin-down.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Tobias Karl, Davide Gatti, Bettina Frohnapfel, Thomas Boehlke
Summary: This study focuses on the application of anisotropic fiber-reinforced composites in lightweight construction, particularly on the evolution of fiber arrangement and orientation during mold filling of fiber suspensions. By introducing a novel closure approach, improved prediction of anisotropic properties and simplified numerical implementation are achieved.
JOURNAL OF RHEOLOGY
(2021)
Article
Mechanics
K. Schaefer, A. Stroh, P. Forooghi, B. Frohnapfel
Summary: The study investigates the topological features of secondary flows over protruding and recessed roughness strips using a parametric forcing approach, showing that a slightly larger wall offset is induced when applied to heterogeneous rough-wall conditions. While the parametric forcing approach requires less computational expense for simulating localized roughness effects, it reveals different physical mechanisms and secondary flow topologies between protruding and recessed roughness strips.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Mechanical
Davide Gatti, Alexander Stroh, Bettina Frohnapfel, Ramis Oerlue
Summary: This study addresses the question of whether spatial resolution effects should be considered in measurements of turbulent wall-bounded flows over rough surfaces in the fully rough regime. By using a direct numerical simulation database, the researchers find that spatial resolution effects are significant in fully rough flows and can be corrected using an appropriate correction scheme.
EXPERIMENTS IN FLUIDS
(2022)
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
Kay Schaefer, Bettina Frohnapfel, Juan Pedro Mellado
Summary: Turbulent mixed convection in channel flows with heterogeneous surfaces is studied using direct numerical simulations. The study finds that the heterogeneous surfaces significantly affect the flow structures, especially in the transition from rolls to cells. Additionally, the heterogeneous surfaces result in slow dynamics of the streamwise rolls.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Lars H. von Deyn, Davide Gatti, Bettina Frohnapfel
Summary: By studying trapezoidal-grooved surfaces of different sizes, we investigated the transition from riblet-like to ridge-like behavior. We discovered multiple drag regimes depending on the size and periodicity of the surface structures. The appropriate definition of the channel height proved crucial in interpreting the drag behavior.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Mechanical
Erik Hansen, Gerda Vaitkunaite, Johannes Schneider, Peter Gumbsch, Bettina Frohnapfel
Summary: While modifying surface contacts can reduce friction, it is challenging to achieve consistent friction behavior in real-life experiments and virtual simulations. This work establishes a digital twin of a pin-on-disk tribometer using real-life measurements and calibrates it to accurately represent the friction behavior. It also uses the Hersey number to validate the method for different dynamic viscosities.
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)
