Article
Mechanics
Erik Lindborg
Summary: This study derives the evolution equation for the mean kinetic energy in a 2-D or 3-D Rayleigh-Benard system and establishes the scaling relations between the Reynolds number and convergence time scale with the Rayleigh number and Prandtl number, respectively. The predictions are validated by comparing with data from numerical simulations.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
X. Y. Jiang, D. W. Gu, C. B. Lee, C. R. Smith, P. F. Linden
Summary: The study explores the laminar-turbulent transition in boundary layers by investigating the evolution of flow structures from 3-D waves to Lambda-vortices. Through numerical simulations of K-regime and bypass transitions, the process of wave-warping and vortex dynamics is examined. The research suggests that adverse pressure gradient conditions lead to a more rapid evolution and stronger viscous-inviscid interaction, ultimately resulting in the development of high-shear layers and warped wave fronts.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Dinar Zaripov, Vladislav Ivashchenko, Rustam Mullyadzhanov, Renfu Li, Nikolay Mikheev, Christian J. Kaehler
Summary: In this study, the mechanism of near-wall reverse flow (NWRF) events in turbulent duct flow at a relatively low Reynolds number Re-tau around 200 was investigated using direct numerical simulations and particle image velocimetry. A conceptual model was proposed to explain the formation of NWRF events, suggesting they are caused by intense hairpin vortices at the interface between high- and low-momentum flow regions. The similarity of flow topologies associated with NWRF events at Re-tau around 200 with those at higher Reynolds numbers indicates a generality of the proposed mechanism.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Peter W. Duck, Sharon O. Stephen
Summary: In this paper, downstream development of small amplitude unsteady disturbances on a Blasius boundary layer is considered. Two completely disparate families of disturbances are identified, with one located deep inside the boundary layer and another at the outer edge. Three-dimensional disturbances are found to have a profound effect on two-dimensional modes, potentially leading to downstream growth.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Ian P. Castro, J. W. Kim, A. Stroh, H. C. Lim
Summary: This study presents data from numerical simulations of channel flow with surface-mounted rectangular ribs, showing the effects of secondary flows induced by the ribs. It is found that the direction of secondary flows is largely independent of rib spacing, while the strength of secondary flows depends on the ratio of rib spacing to rib width and Reynolds number. The topological features of the secondary flow structure and its impact on the flow are also investigated.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
R. Jason Hearst, Charitha M. de Silva, Eda Dogan, Bharathram Ganapathisubramani
Summary: The study on the instantaneous structure of a turbulent boundary layer affected by freestream turbulence revealed that the number and length of uniform-momentum zones decrease with increasing freestream turbulence intensity. The modal velocities associated with the zones are distributed similarly regardless of external flow conditions, indicating a certain resilience of the instantaneous structure to the freestream.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Ulrich Rist, Matthias Weinschenk, Christoph Wenzel
Summary: This paper analyzes the three-dimensional finite-time Lyapunov exponent (FTLE) field of a flat-plate turbulent boundary layer using direct numerical simulation. The study focuses on the regions of minimal stretching between the vortices and shear layers in the turbulent flow field, referred to as Lagrangian areas of minimal stretching (LAMS). The largest LAMS occur near the boundary-layer edge and exhibit increased relative velocity compared to the mean flow. Sweeping events dominate over ejection events above a certain threshold, and both occur in the layer with maximal vortical activity.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Cheng Cheng, Lin Fu
Summary: This paper investigates two fundamental models describing multiscale turbulence interactions and energy-containing motions. The comparison between the statistics from these two models demonstrates their consistency and complementarity. A Gaussian model is proposed to characterize the distribution of streamwise wall-shear stress resulting from attached-eddy superpositions.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jaime Vaquero, Nicolas Renard, Sebastien Deck
Summary: The outer layer dynamics of a high-Reynolds-number boundary layer recovering from non-equilibrium is studied using the multi-resolution approach of zonal detached eddy simulation mode 3. The study finds that most of the outer layer turbulence is accurately reproduced by the simulation and there is a different distribution of turbulent content between the separation region and the redevelopment region.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Aerospace
Yuhan Lu, Jianhan Liang, Zaijie Liu, Hongkang Liu, Chao Yan
Summary: Here, a numerical approach for the three-dimensional global instability analysis of high-speed boundary layer is developed and validated in two cases. The results demonstrate that this approach can accurately predict the wavelength, growth rate, and disturbance amplitude of unstable modes.
AEROSPACE SCIENCE AND TECHNOLOGY
(2023)
Article
Mechanics
H. Yao, G. Papadakis
Summary: This study investigates the role of the laminar/turbulent interface in the interscale energy transfer in a boundary layer undergoing bypass transition, using the Karman-Howarth-Monin-Hill (KHMH) equation. A local binary indicator function is used to detect the interface and define two-point intermittencies. The findings show that the inverse cascade in the streamwise direction is caused by events across the downstream or upstream interfaces of a turbulent spot, and there are significant differences in the energy fluxes between these two regions.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Chris A. Jones, Krzysztof A. Mizerski, Mouloud Kessar
Summary: Anelastic convection at high Rayleigh number in a plane parallel layer with no-slip boundaries is studied, deriving energy and entropy balance equations to develop scaling laws for heat transport and Reynolds number. The appearance of an entropy structure allows for explicit forms of these scaling laws based on the Rayleigh number, Prandtl number, and temperature ratio. Different scaling laws are found depending on whether viscous dissipation primarily occurs in the boundary layers or in the bulk, with numerical simulations comparing theoretical predictions up to a Rayleigh number of 10^7.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Thermodynamics
Yuting Cheng, Jiao Sun, Pi Chen, Wenyi Chen
Summary: This study investigates the shedding structure of a liquid-solid turbulent boundary layer with solid particles using PIV, and finds that the recirculation zone grows larger with increasing yaw angle values. The power spectral density function and proper orthogonal decomposition are used to analyze the near-field, revealing that different angles have an impact on wake shedding structures. The study also observes shearing vortices at the top and base of the pyramid, with sensitivity to variations in the yaw angle.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2023)
Article
Mechanics
Alex Guo, Daniel Floryan, Michael D. Graham
Summary: This study aims to extract and characterize structures in fully developed pipe flow at a friction Reynolds number of Re-tau = 12 400. The results show that these structures exhibit self-similarity in the streamwise and wall-normal directions, and resemble Meyer wavelets. The evidence of self-similarity provided in this study supports Townsend's attached eddy hypothesis.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Y. X. Wang, K. -S. Choi, M. Gaster, C. Atkin, V. Borodulin, Y. Kachanov
Summary: The experimental investigation in a low-turbulence wind tunnel revealed that artificially initiated turbulent spots in a laminar boundary layer over a flat plate quickly developed into hairpin-like structures, increasing in width, length and height downstream. Only disturbances greater than a threshold value evolved into turbulent spots, while others decayed. The rate of development was also influenced by the duration of initial disturbances. Additionally, the behavior of turbulence generation within a turbulent spot was found to be similar to burst events in a turbulent boundary layer.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Physics, Fluids & Plasmas
C. Morrill-Winter, D. T. Squire, J. C. Klewicki, N. Hutchins, M. P. Schultz, I. Marusic
PHYSICAL REVIEW FLUIDS
(2017)
Article
Biotechnology & Applied Microbiology
Kim A. Nolte, Julian Koc, J. M. Barros, Kelli Hunsucker, Michael P. Schultz, G. W. Swain, Axel Rosenhahn
Article
Thermodynamics
Julio M. Barros, Michael P. Schultz, Karen A. Flack
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2018)
Article
Physics, Fluids & Plasmas
Ralph J. Volino, Michael P. Schultz
PHYSICAL REVIEW FLUIDS
(2018)
Article
Biotechnology & Applied Microbiology
Elizabeth A. K. Murphy, Julio M. Barros, Michael P. Schultz, Karen A. Flack, Cecily N. Steppe, Matthew A. Reidenbach
Article
Engineering, Marine
N. Speranza, B. Kidd, M. P. Schultz, I. M. Viola
Article
Mechanics
Kristofer M. Womack, Charles Meneveau, Michael P. Schultz
JOURNAL OF FLUID MECHANICS
(2019)
Article
Thermodynamics
K. A. Flack, M. P. Schultz, J. M. Barros
FLOW TURBULENCE AND COMBUSTION
(2020)
Article
Thermodynamics
Karen A. Flack, Michael P. Schultz, Ralph J. Volino
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2020)
Review
Mechanics
Daniel Chung, Nicholas Hutchins, Michael P. Schultz, Karen A. Flack
Summary: Reliable full-scale prediction of drag due to rough wall-bounded turbulent fluid flow remains a challenge, with at least 10% uncertainty. Recent advances have lowered barriers and are beginning to impact other multiphysical areas, promising increased predictive reliability.
ANNUAL REVIEW OF FLUID MECHANICS, VOL 53
(2021)
Article
Engineering, Marine
James W. Gose, Kevin Golovin, Mathew Boban, Brian Tobelmann, Elizabeth Callison, Julio Barros, Michael P. Schultz, Anish Tuteja, Marc Perlin, Steven L. Ceccio
Summary: In this study, the drag-reducing effect of sprayed superhydrophobic surfaces (SHSs) on two external turbulent boundary layer (TBL) flows was determined. The research found a reduction in skin friction between 8% and 36% in one TBL flow, and an average decrease in overall resistance from 2% to 12% in a towed submersible body with SHS applied, indicating a 4-24% friction drag reduction with SHS application. The results from the towed model were consistent with the drag reduction inferred from near-zero pressure gradient TBL channel flow measurements.
JOURNAL OF SHIP RESEARCH
(2021)
Article
Mechanics
Kristofer M. Womack, Ralph J. Volino, Charles Meneveau, Michael P. Schultz
Summary: This study conducted experiments on flows with regular and random roughness elements and found that there were minor differences in flow statistics between the regular and random arrangements at the same density. The observed differences in surface flow parameters were mainly due to the presence of secondary flows. Contrary to expectations, these secondary flows were present over the random surfaces and not discernible over the regular surfaces. Additionally, the local turbulent boundary layer profiles did not scale with local wall shear stress but appeared to scale with local turbulent shear stress above the roughness canopy.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Biotechnology & Applied Microbiology
Elizabeth A. K. Murphy, Julio M. Barros, Michael P. Schultz, Karen A. Flack, Cecily N. Steppe, Matthew A. Reidenbach
Summary: This study uses high resolution particle image velocimetry to investigate the impact of different types of biofilms on turbulence production, Reynolds shear stress, and rotational flow near the bed. The results show that all biofilms increase these parameters compared to a smooth wall, with non-uniform biofilms having the greatest effect. However, uniform biofilms have a higher drag coefficient compared to non-uniform biofilms.
Article
Mechanics
Ralph J. Volino, Michael P. Schultz
Summary: Measurements were conducted in rough-wall boundary layers subjected to different pressure gradients. The study compared the mean velocity and turbulence quantities profiles and velocity fields between rough- and smooth-wall cases. It was observed that there was outer layer similarity in favorable and zero pressure gradient regions, but significant differences occurred under adverse pressure gradients. The results indicate that similarity could be achieved in adverse pressure gradients by comparing smooth- and rough-wall cases with the same Clauser pressure gradient parameter history.
JOURNAL OF FLUID MECHANICS
(2023)
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)