Article
Mechanics
Meital Geva, Lev Shemer
Summary: The structure of the steady boundary layer in the airflow over young wind waves is studied in detail. The coupling between the spatial evolution of wind waves and wind velocity profiles over the water is analyzed. The roughness of the moving water surface under wind increases with airflow velocity and downstream distance. However, a fully rough boundary layer is obtained for young wind waves.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
D. Passiatore, L. Sciacovelli, P. Cinnella, G. Pascazio
Summary: This study presents an analysis of a hypersonic turbulent boundary layer with a cooled wall using numerical simulations. The results reveal the occurrence of thermal and chemical non-equilibrium phenomena due to the conversion of kinetic energy to internal energy. Turbulent mixing plays a crucial role in sustaining the thermal non-equilibrium.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
D. D. Wangsawijaya, P. Jaiswal, B. Ganapathisubramani
Summary: This study finds that the boundary-layer flow over a porous wall can be seen as a superposition of roughness effects and permeability effects. An empirical formulation is proposed based on independently obtained roughness and permeability length scales to predict the momentum deficit. The decoupling approach used in this study is consistent with recent research on heterogeneous rough surfaces and provides insights into the boundary-layer flow over porous walls.
JOURNAL OF FLUID MECHANICS
(2023)
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
Jose M. Mier, Dimitrios K. Fytanidis, Marcelo H. Garcia
Summary: Oscillatory boundary layer flows over a smooth surface were studied using laser Doppler velocimetry in a large experimental oscillatory flow tunnel to investigate the phase shift Delta phi between bed shear stress and free stream velocity maxima. The study revealed the emergence of a logarithmic profile in transitional OBL flows, with turbulence characteristics approaching equilibrium, unidirectional boundary layer flows. The ensemble-average bed shear stress variation analysis showed different peaks associated with the laminar regime and transition to turbulence, leading to the introduction of a revised Delta phi diagram for the entire range of flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Dimitrios K. Fytanidis, Marcelo H. Garcia, Paul F. Fischer
Summary: Direct numerical simulations were conducted to investigate discrepancies in the literature regarding the phase difference between bed-shear stress and free-stream velocity maxima in oscillatory boundary-layer flows. The simulations revealed that a phase lag occurs due to the delayed and incomplete transition of the flows to a fully turbulent regime. The sensitivity of self-sustained turbulence development on background disturbances was confirmed through simulations at a specific Reynolds number. These findings have implications for environmental fluid mechanics and coastal engineering applications.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Civil
Yashar Rafati, Tian-Jian Hsu, Steve Elgar, Britt Raubenheimer, Ellen Quataert, Ap van Dongeren
Summary: Several models are available for numerical simulation of nearshore hydrodynamics and morphological evolution in the field of science and engineering. One such model, XBeach, is investigated for its skill in simulating erosion during storms by calibrating against observations of waves, currents, and sandbar migration. The sensitivity of the modeled sediment transport to adjustable coefficients highlights the need for further calibration and improvement to achieve accurate predictions.
COASTAL ENGINEERING
(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
Peng-Jun-Yi Zhang, Zhen-Hua Wan, Nan-Sheng Liu, De-Jun Sun, Xi-Yun Lu
Summary: This study investigates the effect of wall cooling on pressure fluctuations in compressible turbulent boundary layers using high-fidelity direct numerical simulations. Opposite effects of wall cooling on pressure fluctuations are found between subsonic/supersonic cases and the hypersonic case. Wall cooling suppresses pressure fluctuations in the former cases, while enhancing them in the latter case, especially near the wall. The main effects of wall cooling can be interpreted by the suppression of the vorticity mode and the enhancement of the acoustic mode.
JOURNAL OF FLUID MECHANICS
(2022)
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
Dehao Xu, Jianchun Wang, Shiyi Chen
Summary: The effects of Reynolds number and wall cooling on correlations between thermodynamic variables in hypersonic turbulent boundary layers are investigated. The Kovasznay decomposition is used to analyze the fluctuating density and temperature. Results show the presence of alternating positive and negative structures in the fluctuating pressure and acoustic modes, as well as streaky entropic structures in the fluctuating entropy and entropic modes near the wall. Correlations involving density and temperature are primarily contributed by entropic modes. Fluctuating temperature is strongly positively correlated with streamwise velocity near the wall in strongly cooled wall cases due to the presence of alternating structures.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Ocean
Yuzhu Li, David R. Fuhrman
Summary: The study investigates the instabilities of deep-water wave trains, focusing on the two-dimensional Benjamin-Feir instability and the three-dimensional crescent waves. Numerical simulations are conducted to explore the generation and development of wave instabilities, including the wave breaking process.
JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING-TRANSACTIONS OF THE ASME
(2022)
Article
Engineering, Civil
Titi Sui, V. S. Ozgur Kirca, B. Mutlu Sumer, Stefan Carstensen, David R. Fuhrman
Summary: This paper presents the experimental results of wave-induced liquefaction in silt and seashell mixtures. The experiments showed that the seashell content has a significant influence on liquefaction, with increasing seashell content leading to decreased liquefaction susceptibility. The study also identified a limiting value for seashell content, beyond which the mixture becomes liquefaction resistant.
COASTAL ENGINEERING
(2022)
Article
Mechanics
Yuzhu Li, David R. Fuhrman
Summary: This study simulates the incipient wave breaking on a vertical circular pile using a Reynolds stress-omega turbulence model. The results show that the turbulence closure model does not affect the breaking point and peak force, but proper turbulence modeling is required for the prediction of secondary load cycle. The Reynolds stress-omega model predicts the secondary load cycle more accurately than the stabilized two-equation k-omega turbulence model.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Environmental Sciences
Bjarke Eltard Larsen, Mustafa Ali Abdullah Al-Obaidi, Hasan Gokhan Guler, Stefan Carstensen, Koray Deniz Goral, Erik Damgaard Christensen, Nils B. Kerpen, Torsten Schlurmann, David R. Fuhrman
Summary: This paper presents experimental measurements of beaching times for buoyant microplastic particles released in different areas of the beach. The study finds that the microplastics travel onshore with a velocity close to the Lagrangian fluid particle velocity before breaking, and their velocities increase and become closer to the wave celerity in the surf zone. It is also observed that particles with lower Dean numbers are transported at higher mean velocities.
MARINE POLLUTION BULLETIN
(2023)
Article
Engineering, Marine
Karen B. B. Burgaard, Stefan Carstensen, David R. R. Fuhrman, Camille Saurel, Finbarr G. G. O'Neill
Summary: This study provides morphological data and estimates of the settling velocity and drag coefficient of sea stars (Asterias rubens) in Limfjord, Denmark. A geometric model describing the sea star is introduced, and the thickness and arm width are determined as linear functions of arm length. The geometric model accurately predicts the volume and mass of the sea stars, which is in agreement with experimental measurements. The mean sea star density is determined to be 1095 kg/m(3), the mean drag coefficient is estimated to be 2.3, and the settling velocity varies with the square root of its size.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2023)
Article
Engineering, Civil
Xueying Yu, Yanlin Shao, David R. Fuhrman, Yunxing Zhang
Summary: A novel two-dimensional numerical wave tank based on the two-phase Navier-Stokes equations is presented in this paper. The GHPC method, originally proposed for the constant-coefficient Poisson equation, is demonstrated to be applicable for two-phase flow problems by introducing a pressure-correction method. The accuracy and convergence rate of the numerical model are validated through wave generation and propagation, as well as comparisons with benchmark results for wave-structure-interaction problems.
COASTAL ENGINEERING
(2023)
Article
Engineering, Civil
Bjarke Eltard Larsen, Dominic A. van der A, Rex Carstensen, Stefan Carstensen, David R. Fuhrman
Summary: Experimental results on shoreface nourishment scenarios are presented, where the effects of nourishment placement and timing on long-term cross-shore profile development are investigated. Four different nourishment scenarios are tested, and the results show that the erosion of the shoreline slows under all scenarios. The two cases with nourishment placed along the bar reduce shoreline erosion more compared to the two cases with nourishment in the trough.
COASTAL ENGINEERING
(2023)
Article
Engineering, Civil
Bjarke Eltard Larsen, David R. Fuhrman
Summary: The study investigates the performance of a recently developed stabilized turbulence closure model in the computational fluid dynamics simulation of cross-shore sediment transport and breaker bar morphology. Comparisons with experiments and simulations using standard turbulence closure show major improvements in predicted breaker bar position and height using the stabilized turbulence model. The study highlights the importance of proper turbulence modeling for accurate CFD prediction of cross-shore sediment transport and profile morphology.
COASTAL ENGINEERING
(2023)
Article
Engineering, Environmental
Koray Deniz Goral, Hasan Gokhan Guler, Bjarke Eltard Larsen, Stefan Carstensen, Erik Damgaard Christensen, Nils B. B. Kerpen, Torsten Schlurmann, David R. R. Fuhrman
Summary: This research demonstrates that the Shields diagram is applicable for predicting incipient motion thresholds of both native sediments and microplastic particles. The study investigates various regular and irregular microplastic particle groups in a flume and combines data from the literature for analysis. A new framework is proposed to account for the effects of static friction, hydraulic roughness, and hiding-exposure on predicting incipient motion conditions for foreign particles, reconciling them with the Shields diagram.
ENVIRONMENTAL SCIENCE & TECHNOLOGY
(2023)
Article
Engineering, Civil
Titi Sui, B. Mutlu Sumer, V. S. Ozgur Kirca, Stefan Carstensen, Jinhai Zheng, David R. Fuhrman
Summary: This paper presents the results of an experimental investigation on wave-induced liquefaction in the case of multiple wave exposures. The experiments show that the first strongest wave climate leads to liquefaction, regardless of prior wave exposures. It is also found that subsequent wave exposures do not liquefy the soil. Moreover, the dissipation of accumulated pore pressure is slower in uninterrupted wave exposures compared to interrupted ones.
COASTAL ENGINEERING
(2023)
Article
Engineering, Civil
Bjarke Eltard Larsen, David R. Fuhrman
Summary: This paper re-examines empirical formulations for predicting equilibrium scour depths and time scales for monopiles. Based on physical grounds, it argues that dimensionless time scales should scale proportionally to the Shields parameter raised to the -3/2 power. Existing formulations based on laboratory experiments, which have a stronger power dependence, may be unreliable when extrapolated to field scales. The paper re-analyzes existing data sets and develops novel parameterizations that are in line with the proposed argument.
COASTAL ENGINEERING
(2023)
Article
Environmental Sciences
Koray Deniz Goral, Hasan Gokhan Guler, Bjarke Eltard Larsen, Stefan Carstensen, Erik Damgaard Christensen, Nils B. Kerpen, Torsten Schlurmann, David R. Fuhrman
Summary: This study experimentally measured the settling velocities of 66 groups of microplastic particles, including 58 regular and 8 irregular shapes. The study developed novel parameterizations and predictive drag coefficient formulations for both regular and irregular particle shapes, considering preferential settling orientation. The results showed higher accuracy compared to previous predictive formulations. The method for predicting the settling velocity of irregularly-shaped microplastic particles was demonstrated to be applicable to natural sediments in the Appendix.
ENVIRONMENTAL RESEARCH
(2023)
Article
Mechanics
David R. Fuhrman, Mathias Klahn, Yanyan Zhai
Summary: The conventional method for computing the probability density function (p.d.f.) of a nonlinear, irregular water wave field is the approximate Gram-Charlier series solution by Longuet-Higgins. This paper revisits the derivation of the p.d.f. to second order using moment and cumulant generating functions and shows that the approximate solution matches the solution derived from the moment generating function. It is also shown that the approximation employed by Longuet-Higgins is unnecessary and the exact second-order p.d.f. can be represented in terms of the Airy function.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Marine
Karen B. Burgaard, Stefan Carstensen, David R. Fuhrman, Bjarke E. Larsen, Finbarr G. O'Neill
Summary: An experimental and numerical study was conducted to investigate the flow behavior upstream and downstream of a disc-attached cylinder near a wall. The experimental results showed that the mean flow could be considered two-dimensional at a distance greater than the diameter of the cylinder. Both the experimental and numerical simulations found an increase in the peak amplitudes of the power spectra of vertical velocity fluctuations at a distance of 3.75 times the diameter from the centerline of the disc, caused by vortices transported by a transverse flow related to the disc.
Article
Fisheries
Karen B. Burgaard, Stefan Carstensen, David R. Fuhrman, Camille Saurel, Finbarr G. O. 'Neill
Summary: This study demonstrates the influence of hydrodynamics on the fishing performance of towed demersal fishing gears. Sea trials in the sea star fishery show that modifications to the gear design can alter the hydrodynamics of the turbulent wake and consequently affect the catching performance of trawl gears. The trials investigate the effect of the gap between the towing beam and the seabed, and the size of the beam on cockle and mussel beds.
FISHERIES RESEARCH
(2023)