Article
Acoustics
Weiqi Shen, Trushant K. Patel, Steven A. E. Miller
Summary: This study introduces a time-domain BBSAN model based on the vector Green's function solution, utilizing LES databases and Proper orthogonal decomposition to analyze shock-associated noise in off-design supersonic jets. By analyzing the predominant POD modes and noise source contour plots, the key features of BBSAN are revealed.
JOURNAL OF SOUND AND VIBRATION
(2021)
Article
Environmental Sciences
Jong -Won Kim, Jong-Jin Baik, Seung-Bu Park, Beom-Soon Han
Summary: The variability of building heights has significant impacts on urban flow and air quality. Numerical simulations reveal that increasing building-height variability leads to decreased pollutant concentration at pedestrian level and increased spatial variability. Building-height variability also greatly affects turbulence intensity, vertical turbulent momentum, and pollutant fluxes.
ATMOSPHERIC POLLUTION RESEARCH
(2023)
Article
Engineering, Multidisciplinary
Haoju Lin, Hui Liu, Peng Wei
Summary: This work proposes a parallel parameterized level set topology optimization framework for large-scale structures with unstructured meshes, which addresses the adaptability to structures with arbitrary geometries and complex boundary conditions. The framework combines distributed memory parallel computing technology and parameterized level set topology optimization using unstructured meshes. Several means, including shape functions, directed acyclic graph data structure, direct imposition of passive domain and boundary conditions on geometry entities, and multiple averaging filter, are utilized. Computing tests demonstrate the stability, efficiency, scalability, and potential for discovering new structure styles of the framework.
COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING
(2022)
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
Optics
Mengyue Xu, Yuntao Zhu, Jin Tang, Jingyi Wang, Lin Liu, Huixiao Ma, Siyuan Yu, Bofang Zheng, Xinlun Cai
Summary: In the past decade, coherent technology has been used in long-haul transmission systems to meet the growing demand for capacity at lower costs per bit. A high-performance coherent modulator with high data rates, wide bandwidth, small footprint, and low power operation is proposed. The device allows for attojoule-per-bit level electrical energy consumption over transmission distances above 1000 km, opening opportunities for lower-cost and capacity-intensive coherent systems that consume ultra-low power, support high data rate, and work in small spaces.
Article
Engineering, Chemical
Linna Jin, Yuhui Cao
Summary: This study applied the improved delayed detached-eddy simulation (IDDES) method to predict turbulent mixing in a confined impinging-jet mixer. The results showed good agreement with experimental data and provided insights on the coherent structures and their effects on turbulence statistics and mixing efficiency.
CHEMICAL ENGINEERING SCIENCE
(2022)
Article
Mechanics
J. G. Chen, R. A. Antonia, Y. Zhou
Summary: An equation that quantifies the relationship between the principal derivative of the Reynolds shear stress and large-scale vorticity fluxes is developed and validated using experimental data. The study reveals that when large-scale vortices dominate, the Reynolds shear stress associated with coherent motion can be approximated by the conventional Reynolds shear stress. The latter is mainly determined by the imbalance between the dynamic pressure arising from streamwise non-homogeneity induced by large-scale vortical structures and the lateral coherent vorticity flux.
Article
Geosciences, Multidisciplinary
H. Dashtpeyma, B. J. MacVicar
Summary: Pool-riffle units are natural topographical elements of rivers. This study uses Large Eddy Simulations to investigate the dynamics of flow over straight riffles and proposes a physical mechanism for the observed high near-bed velocities. The results provide a novel explanation for near-bed high velocity flow observations in natural pool-riffles and reveal the significance of turbulent shear stresses in the head of a pool.
JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE
(2023)
Article
Mechanics
Milad Samie, Vlad Aparece-Scutariu, Philippe Lavoie, Dong-hyuk Shin, Andrew Pollard
Summary: This study uses direct numerical simulation to investigate three-dimensional vortical and very-large-scale coherent structures in a turbulent round jet at a Reynolds number of 7300. The results show the importance of horseshoe vortices in the jet and the existence of symmetric and asymmetric horseshoe vortices that affect the high and low momentum regions in the flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Computer Science, Interdisciplinary Applications
Tianrun Gao, Huihe Qiu, Lin Fu
Summary: Fluid-Structure Interaction (FSI) is a critical problem in ocean engineering, and the smoothed particle hydrodynamics (SPH) method has been employed for FSI problems due to its advantages in handling multi-physics problems. The Adaptive Particle Refinement (APR) method can improve the efficiency of SPH, and this study further improves the APR method by developing new algorithms. The improved APR method with a large refinement scale ratio and a new free-surface detection strategy demonstrates great potential in efficiently and accurately simulating complex FSI problems.
JOURNAL OF COMPUTATIONAL PHYSICS
(2023)
Article
Engineering, Chemical
Hannes Bauer, Johannes Khinast
Summary: Twin-screw extruders are known for their good mixing performance, but the actual mixing mechanism remains largely unexplored due to the complexity of the screw geometry. This study uses Lagrangian Coherent Structures to understand laminar mixing in various elements of twin-screw extruders and offers a novel viewpoint for geometry optimization.
CHEMICAL ENGINEERING SCIENCE
(2022)
Article
Mechanics
Ming Yu, Dong Sun, QingQing Zhou, PengXin Liu, XianXu Yuan
Summary: In this study, we used direct numerical simulation databases to investigate the evolution of turbulent statistics and coherent structures in hypersonic turbulent boundary layers subjected to oblique shock waves. We found that large-scale structures are amplified within the interaction zone and gradually decay downstream, leading to discrepancies between the predictions of Reynolds-Averaged Navier-Stokes simulations and the actual flow behavior. To address this issue, we proposed refining the model parameters as functions of wall pressure and other flow quantities, leading to improved accuracy in predicting various flow properties downstream of the interaction zone.
Article
Thermodynamics
Kristian Ronnberg, Christophe Duwig
Summary: In this study, heat transfer arising from an impinging jet at a Reynolds number of 5000 was investigated through Large Eddy Simulation (LES). The heat transfer was found to be distributed according to a gamma distribution, and was decomposed using proper orthogonal decomposition (POD) and extended proper orthogonal decomposition (EPOD). The results showed that distinct flow features were associated with low order heat transfer modes, with dominant modes identified as ring-like vortex structures. Reconstruction of the heat transfer field revealed radially outward moving structures with a phase velocity of 0.23 U-b.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2021)
Article
Engineering, Civil
Pengcheng Zou, Shuyang Cao, Jinxin Cao
Summary: In this study, the spanwise correlation and coherent structure of separated flow around a rectangular cylinder with a side ratio of B/D = 5 were numerically investigated using Large Eddy Simulation (LES) at Reynolds number Re = 22,000. The results showed the existence of a spanwise coherent flow structure associated with longitudinal vortices, with a wavelength of around 1.4D. A spanwise length of 3D was found to be sufficient in eliminating the influence of the spanwise coherent flow structure on the global aerodynamic parameters. The spanwise correlations of sectional forces and surface pressures decayed with increasing spanwise distance, and a finer spanwise resolution resulted in decreased spanwise correlations within the investigated range. The results also emphasized the need to consider multiple interacting factors, such as numerical method, three-dimensional grid discretization, and turbulence model, when selecting the spanwise resolution.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2022)
Article
Thermodynamics
Xiaonan Chen, Koji Iwano, Yasuhiko Sakai, Yasumasa Ito
Summary: This study investigated the meandering bend features of large-scale structures (LSMs and VLSMs) and their relationship with small-scale hairpin vortex structures in a turbulent boundary layer. The results showed that the meandering of LSMs and VLSMs was highly related to the distribution of hairpin vortex packets, while the asymmetry of small-scale hairpin vortex had nearly no effect on the meandering bend of LSMs and VLSMs.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Engineering, Ocean
Aristos Christou, Zhihua Xie, Thorsten Stoesser, Pablo Ouro
Summary: In this study, the Hydro3D in-house large-eddy simulation code was refined to investigate wave structure interaction. The code accurately simulated solitary waves generation and propagation in a numerical wave tank, as well as wave interaction with both infinitely wide and finite square plates. Three-dimensional effects, such as span-wise flow and unique flow structures near the plate, were identified, along with variations in hydrodynamic forces and free-surface elevations when the plate is fixed at different angles of attack.
APPLIED OCEAN RESEARCH
(2021)
Article
Thermodynamics
Arthur Hajaali, Thorsten Stoesser
Summary: The mean and instantaneous flow separation of two different three-dimensional asymmetric diffusers were analyzed using large-eddy simulations, showing good agreement with experimental data. The study further quantifies flow separation behavior and unsteadiness, revealing the volume portion in which the instantaneous reversal flow evolves. Analysis of power density spectra of time series indicates the periodicity of the growth and reduction phases of flow separation within the diffusers.
FLOW TURBULENCE AND COMBUSTION
(2022)
Article
Engineering, Marine
Xingsen Guo, Tingkai Nian, Thorsten Stoesser
Summary: This paper investigates the impact forces induced by submarine landslides on a golfball-type dimpled pipeline surface using a computational fluid dynamics approach. The study finds that the golfball-type dimpled pipelines experience reduced drag forces and suppress lift force variations. A methodology for predicting the drag reduction and necessary conditions for lift force periodic vibrations are provided. Additionally, the paper reveals the full life cycle of vortices shed from the pipeline and the hydrodynamics during landslides impact on pipelines.
Article
Engineering, Marine
Xingsen Guo, Thorsten Stoesser, Tingkai Nian, Yonggang Jia, Xiaolei Liu
Summary: This paper investigates the influence of pipeline surface roughness on the interaction between submarine landslides and pipelines. The study establishes a methodology to estimate peak impact forces, providing a basis for risk assessment of submarine pipelines.
Article
Computer Science, Interdisciplinary Applications
Zhihua Xie, Pengzhi Lin, Thorsten Stoesser
Summary: A conservative and consistent three-dimensional Cartesian cut-cell method is proposed to reduce spurious pressure oscillations in moving body simulations. The method improves the moving body algorithm and enforces strict conservation of mass and momentum through pressure-velocity coupling. A consistent mass and momentum flux computation is employed, and an implicit time integration scheme is used to prevent numerical instability.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Mechanics
Yan Liu, T. Stoesser, H. Fang
Summary: This study investigates the effect of secondary currents on friction factor, statistics, and large-scale turbulent motion in partially filled pipes using large-eddy simulations. The results show that secondary currents originate from the corner between the free surface and the pipe walls, and their presence reduces the friction factor and the strength of near-wall structures. Therefore, partially filled pipe flows have lower drag and turbulent energy compared to fully filled pipe flows.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Civil
Congfang Ai, Yuxiang Ma, Changfu Yuan, Zhihua Xie, Guohai Dong, Thorsten Stoesser
Summary: This paper presents a simulation study of a solitary wave propagating over a submerged horizontal plate using a non-hydrostatic model and a high-resolution advection scheme. The results show that the length of the plate has a significant influence on the characteristics of vortex shedding and evolution, with longer plates resulting in more pronounced vortex structures.
JOURNAL OF HYDRAULIC RESEARCH
(2022)
Article
Engineering, Marine
Congfang Ai, Yuxiang Ma, Changfu Yuan, Zhihua Xie, Guohai Dong, Thorsten Stoesser
Summary: This paper presents a three-dimensional non-hydrostatic model for predicting the interaction between nonlinear waves and fixed floating structures. A new numerical algorithm is proposed to handle floating structures, and the model is validated by comparing its results with experimental data and other models.
Article
Mechanics
Yan Liu, Thorsten Stoesser, Hongwei Fang
Summary: This study investigates the response of turbulent flow and water surface fluctuations in partially filled pipes through large eddy simulations. The results show that as the water depth increases, the strength of the main secondary flow and the magnitude of water surface fluctuations also increase. Pre-multiplied spectra provide further evidence of the origin of the surface waves. Analysis of the wavenumber-frequency spectra reveals different types of surface waves.
Article
Environmental Sciences
Chenwei Zhao, Pablo Ouro, Thorsten Stoesser, Subhasish Dey, Hongwei Fang
Summary: Numerical simulations were conducted to explore the effects of natural bed roughness on bedload transport. The results show that as bed roughness increases, there is a shift in the velocity profiles, an increase in Reynolds stresses, and the fragmentation of coherent structures. The resting time of saltating particles increases while their saltation length, velocity, and angular velocity decrease.
WATER RESOURCES RESEARCH
(2022)
Article
Engineering, Civil
Filipa Adzic, Thorsten Stoesser, Yan Liu, Zhihua Xie
Summary: Large-eddy simulations were performed to study the characteristics of supercritical flow in a straight-wall, open-channel contraction. The results revealed that secondary currents in the contraction redistributed momentum, resulting in local up-and down-flows, and the energy loss was mainly caused by pressure drag.
JOURNAL OF HYDRAULIC RESEARCH
(2022)
Article
Engineering, Ocean
Xingsen Guo, Thorsten Stoesser, Cheng Zhang, Cuiwei Fu, Tingkai Nian
Summary: This study investigates the interaction between submarine landslides, ambient water, and pipelines using computational fluid dynamics (CFD) modeling and physical flume experiments. The effects of different boundary conditions on the impact forces on pipelines are explored, and the mechanism behind these force changes is explained through the analysis of velocity field, pressure field, and streamlines. A method for determining boundary conditions is proposed, providing a basis for optimizing CFD modeling in submarine landslide-pipeline interactions.
APPLIED OCEAN RESEARCH
(2022)
Article
Computer Science, Interdisciplinary Applications
Xingsen Guo, Thorsten Stoesser, Defeng Zheng, Qianyu Luo, Xiaolei Liu, Tingkai Nian
Summary: In this study, the method of computational fluid dynamics (CFD) was used to simulate a fluidized submarine landslide with shear thinning non-Newtonian fluids under different contact conditions. The accuracy of the CFD method was validated and various experiments were systematically performed. The stress state and causes of the submarine landslide mass during its movement in ambient water were revealed, and the submarine landslide-seabed contact relation was identified as a decisive influencing factor. Furthermore, a methodology based on energy conservation was presented to predict the run-out distance of the submarine landslide mass, and equations to quantify the process were established and validated by numerical results. This provides a significant basis for the prediction of marine engineering geological and hydrodynamic hazards related to submarine landslides.
COMPUTERS AND GEOTECHNICS
(2023)
Article
Water Resources
Saad Mulahasan, May Samir Saleh, Sadiq S. Muhsun
Summary: A research was conducted to investigate flow parameters around an isolated permeable spur dike using complementary numerical and experimental models. The study found that the medium's properties have a slight effect on water velocity for low flow rates, but become more significant for high flow rates. Computational and experimental results showed good agreement in terms of water surface profiles and velocity distribution.
INTERNATIONAL JOURNAL OF RIVER BASIN MANAGEMENT
(2023)
Article
Physics, Fluids & Plasmas
Razieh Jalalabadi, Thorsten Stoesser
Summary: This study examines the Reynolds and dispersive shear stresses in turbulent flow over spanwise-aligned square bars in an open channel flow. The analysis of large-eddy simulation results for two different bar spacings reveals that the contribution of Reynolds shear stress to the momentum loss is greater than that of the dispersive shear stress. However, by increasing the bars spacing, the contribution of the dispersive shear stress increases while the Reynolds shear stress contribution decreases. The study also investigates the dynamics of the flow and finds that there is a momentum source below the crest of the bars and a momentum sink above them, leading to acceleration or deceleration of flow. Furthermore, the quantification of the three components of total kinetic energy shows that the largest contribution is from the mean flow, and by increasing the bar spacing, the contributions of turbulent and wake kinetic energy increase while the kinetic energy of the mean flow decreases.