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
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
Biology
Nurul A. Zainal Abidin, Eric K. W. Poon, Crispin Szydzik, Mariia Timofeeva, Farzan Akbaridoust, Rose J. Brazilek, Francisco J. Tovar Lopez, Xiao Ma, Chitrarth Lav, Ivan Marusic, Philip E. Thompson, Arnan Mitchell, Andrew S. H. Ooi, Justin R. Hamilton, Warwick S. Nesbitt
Summary: This study reveals that platelets can directly sense acute changes in free-flow extensional strain independent of other factors. Mechanosensitive channels and calcium signaling are involved in this process. Moreover, extensional strain sensing plays a significant priming role in platelet activation and thrombosis.
Article
Thermodynamics
Yu Xia, Wagih Abu Rowin, Thomas Jelly, Ivan Marusic, Nicholas Hutchins
Summary: In this study, simulations and experiments are used to investigate the spatial and temporal attenuation of cold wire sensors. The results show that increasing the wire length attenuates the variance of temperature fluctuations but does not affect the mean temperature. The temporal attenuation of temperature fluctuations becomes more significant as the wire aspect ratio decreases below 1000. The attenuation due to insufficient wire aspect ratios affects all energy scales in the boundary layer. Maintaining the viscous-scaled wire length constant and using smaller diameter wires can better resolve temperature fluctuations by sacrificing spatial resolution.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Mechanics
Xuebo Li, Nicholas Hutchins, Xiaojing Zheng, Ivan Marusic, Woutijn J. Baars
Summary: A large-scale array of measuring instruments was used to study the statistical structure of turbulence structures in different stability conditions. The researchers found a self-similar range of turbulence structures and analyzed the scale-dependent inclination angle in the streamwise/wall-normal plane. The results showed that the inclination angle and aspect ratio of the structures were highly sensitive to the stability parameter.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Civil
Andrea Zampiron, Stuart M. Cameron, Mark T. Stewart, Ivan Marusic, Vladimir I. Nikora
Summary: The channel length required for the development of the flow is important in designing hydraulic structures or planning research experiments. However, information on flow development length (L-D) is scarce and its definition remains unclear. This paper offers a physics-based definition for L-D and presents results of laboratory studies to provide guidance on its quantitative assessment. The results suggest that different flow characteristics require different lengths of L-D, with some requiring up to 150 flow depths.
JOURNAL OF HYDRAULIC RESEARCH
(2023)
Article
Physics, Fluids & Plasmas
A. Chahine, J. Sebilleau, R. Mathis, D. Legendre
Summary: This study presents an experimental investigation of droplet sliding under laminar or turbulent airflow. The onset of sliding is described using a critical Weber number based on the mean airflow velocity, which depends on the contact angle hysteresis and drag coefficient. The experimental results show good agreement with data from previous studies, and the transitions between different droplet shapes during sliding are characterized using a phase diagram.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Hematology
Nurul A. Zainal Abidin, Mariia Timofeeva, Crispin Szydzik, Farzan Akbaridoust, Chitrarth Lav, Ivan Marusic, Arnan Mitchell, Justin R. Hamilton, Andrew S. H. Ooi, Warwick S. Nesbitt
Summary: Researchers have developed a microfluidic assay to study platelet mechanotransduction in the absence of surface adhesions. They found that platelets are highly sensitive to extensional strain rates and respond to the rate of change in strain. The actin-based cytoskeleton and microtubules play a key role in platelet mechanotransduction under extensional strain.
RESEARCH AND PRACTICE IN THROMBOSIS AND HAEMOSTASIS
(2023)
Article
Behavioral Sciences
Patricia Henriquez-Piskulich, Devi Stuart-Fox, Mark Elgar, Ivan Marusic, Amanda M. Franklin
Summary: Animals with glossy surfaces may have evolved their appearance as a protection against predators when they are moving. Praying mantids were less likely to attack and accurately strike targets that were glossy and moving fast. This study provides empirical evidence that glossiness may offer protection for fast moving animals against predation.
BEHAVIORAL ECOLOGY
(2023)
Article
Thermodynamics
Thomas O. Jelly, Massimiliano Nardini, Marco Rosenzweig, John Leggett, Ivan Marusic, Richard D. Sandberg
Summary: This study investigates the impact of blade surface roughness on the aero-thermal performance of a high-pressure turbine vane using highly-resolved Large-Eddy Simulations. The study reveals that blade surface roughness affects boundary layer transition mechanisms, wall shear stress, blade surface heat flux, and turbulence kinetic energy and total pressure losses in the wake. However, the pressure-side surface of the blade remains relatively unaffected, even for the largest roughness amplitude.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Mathematics, Applied
S. Chernyshenko
Summary: The well-known background flow method proposed by Doering and Constantin (1994, 1995) is a special case of the auxiliary functional method introduced by Chernyshenko et al. (2014). Chernyshenko (2022) demonstrated that the bounds obtained by the direct method described by Seis (2015) can also be obtained using the auxiliary functional method and, consequently, the background flow method when the auxiliary functional is quadratic. This note outlines a technique to obtain the background flow and auxiliary functional when a proof of a bound for infinite time average by the direct method is known, by applying it to the case of the Nusselt number bound for infinite-Prandtl-number Rayleigh-Benard convection obtained by Otto and Seis (2011).
PHYSICA D-NONLINEAR PHENOMENA
(2023)
Article
Physics, Fluids & Plasmas
Sean Symon, Anagha Madhusudanan, Simon J. Illingworth, Ivan Marusic
Summary: By comparing with direct numerical simulation data, we have compared the predictions obtained from resolvent analysis with and without an eddy viscosity model for turbulent channel flow at Re tau = 550. The standard resolvent identifies energetic regions of the flow, while the eddy resolvent is low rank when the resulting projection of the leading eddy resolvent mode onto the leading mode from spectral proper orthogonal decomposition is maximum. The eddy resolvent also correctly identifies the most energetic wave speed for certain scales, but neither analysis reliably predicts the most energetic wave speed or mode shapes for other scales.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Mechanics
Rahul Deshpande, Charitha M. de Silva, Ivan Marusic
Summary: We provide experimental evidence that the superstructures in turbulent boundary layers are made up of smaller coherent motions that are geometrically self-similar. Through analysis of high Reynolds number particle image velocimetry datasets, we identify and analyze instantaneous superstructures capable of capturing elongated motions up to 12 times the boundary layer thickness. A new approach is taken to identify the constituent motions of the superstructures, by analyzing the wall-normal velocity fluctuations within these long motions. The findings support data-driven modeling of these dynamically significant motions using coherent structure-based models.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
A. Rouhi, M. K. Fu, D. Chandran, A. Zampiron, A. J. Smits, I. Marusic
Summary: Turbulent drag reduction through streamwise travelling waves is investigated over a wide range of Reynolds numbers. Wall-resolved large-eddy simulations are conducted to examine how the frequency and wavenumber of the travelling wave influence the drag reduction. The study finds that the level of turbulence attenuation, and hence drag reduction, changes with the near-wall Stokes layer protrusion height. A range of frequencies is identified where the Stokes layer attenuates turbulence and increases the drag reduction, while outside this range, the strong Stokes shear strain leads to a drop in drag reduction.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Fluids & Plasmas
A. Chahine, J. Sebilleau, R. Mathis, D. Legendre
Summary: This paper focuses on the specific motion observed for glycerin droplets sliding on a horizontal hydrophobic substrate under the influence of a shear flow. The droplets elongate in the flow direction, forming a rivulet shape and developing waves on the sheared surface. This motion mechanism resembles the movement of a caterpillar. The droplets can potentially break up into multiple droplets and also coalesce.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Biochemical Research Methods
Aravind George, Farzan Akbaridoust, Nurul A. Zainal Abidin, Warwick S. Nesbitt, Ivan Marusic
Summary: Hydrodynamic trapping of particles in micro-nano scale applications has provided significant insights. Among non-contact methods, image-based real-time control in cross-slot microfluidic devices shows promise for single cellular assays. Experiments in different channels with varying control delay and magnification achieved sustained trapping of 5 μm diameter particles at high strain rates. The maximum attainable strain rate depends on the control delay and particle resolution, and with further improvements, higher strain rates can be achieved for single cellular assay studies.
