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
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
Wenkang Wang, Chong Pan, Jinjun Wang
Summary: The study investigates the role of large-scale motions (LSMs) in energy transfer using wall-parallel velocity fields at low-to-moderate Reynolds number. An anisotropic filter is designed to explore energy flux, revealing a strong connection between large-scale energy flux events and LSMs. The findings suggest that the meandering nature of LSMs could play a determining role in the process of large-scale energy transfer.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Green & Sustainable Science & Technology
Brooke J. Stanislawski, Regis Thedin, Ashesh Sharma, Emmanuel Branlard, Ganesh Vijayakumar, Michael A. Sprague
Summary: As wind turbines become larger, the fluctuations in inflow have a significant impact on structural loading. The integral length scale, which represents the average size of the largest turbulent eddies, characterizes these fluctuations. Current design standards do not account for the varying integral length scales in turbine inflows. Using large-eddy simulations, we investigate the effects of turbulence with varying integral length scales on the loads of a 15-MW wind turbine. The results show that turbulence has a much greater impact on rotor and tower loads compared to mean shear profiles. Increasing the integral length scale can reduce blade root flapwise moments and rotor and tower loads. However, increasing the integral length scale beyond a certain point increases other loads and decreases some moments. Additionally, turbulence intensity has a larger influence on turbine loads than integral length scales. This study suggests that design standards should consider the varying integral length scales for accurate characterization of wind turbine loading in turbulent inflow conditions.
Article
Mechanics
Rahul Deshpande, Dileep Chandran, Alexander J. Smits, Ivan Marusic
Summary: This study investigates the role of inter-scale interactions in the high-Reynolds-number skin-friction drag reduction strategy. It is found that imposing low-frequency streamwise travelling waves at the wall to actuate the drag generating outer scales is more energy efficient than targeting the drag producing inner scales. The study shows that increased drag reduction is associated with increased coupling between the inner and outer scales through manipulation of the phase relationships. It is also found that this enhancement of nonlinear coupling occurs with increasing Reynolds number, indicating improved efficacy of the energy-efficient drag reduction strategy at very high Reynolds numbers.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
C. Chan, R. C. Chin
Summary: The study reveals that MVGs can create high-speed and low-speed regions through PVPs in a turbulent boundary layer, with varying skin friction in different areas. In addition, pre-processed energy spectra analysis shows that the velocity fluctuations induced by MVGs are mainly influenced by large-scale modes that span wavelengths and MVG lengths, but the energy peak eventually repositions to the near-wall streak scale in the streamwise direction.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Yanguang Long, Jinjun Wang, Chong Pan
Summary: The study reveals the significant impact of large-scale motions on the turbulent/nonturbulent interface and turbulent entrainment in turbulent boundary layers. High-speed large-scale motions enhance the engulfment process and result in a more distorted TNTI. These mechanisms are universal for turbulent boundary layers with different wall shapes.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
K. R. Maryada, S. W. Armfield, P. Dhopade, S. E. Norris
Summary: This study investigates the coherence of turbulent fluctuations in a turbulent vertical natural convection boundary layer immersed in a stably stratified medium. The results show that streamwise velocity fluctuations exhibit coherence over large streamwise distances, thanks to large-scale motions (LSMs) observed in the flow. The LSMs have significant meandering and contribute significantly to turbulence production in the outer layer.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Ian Jacobi, Daniel Chung, Subrahmanyam Duvvuri, Beverley J. McKeon
Summary: This study presents a framework for predicting the interactions between motion and stress fluctuations in wall turbulence, derived from approximations to the Navier-Stokes equations. The model predictions are found to be consistent with observations, suggesting an effective approach for predicting the relationship between different-scale motions and stresses in wall turbulence.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
J. Haerter, D. S. Martinez, R. Poser, B. Weigand, G. Lamanna
Summary: This study verifies the assumptions of theoretical studies by using PIV to measure the velocity in two different porosity porous models at different Reynolds numbers. The results indicate that large-scale turbulent structures generated by the interaction with a turbulent outer flow exist and rapidly decay within the porous medium, validating closure models for volume-averaged computational studies.
Article
Engineering, Marine
Cong Wang, Morteza Gharib
Summary: The dynamic free-slip surface method can manipulate the turbulent boundary layer (TBL) and achieve a significant drag reduction effect on water vehicles. The optimal setting of control parameters, particularly a large Weber number, is crucial for maximizing the drag reduction effect.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2022)
Article
Mechanics
Sourabh S. Diwan, Jonathan F. Morrison
Summary: The study proposed a three-layer asymptotic structure for turbulent pipe flow, revealing the existence of a Reynolds-number-invariant logarithmic region for the streamwise mean velocity and variance in terms of intermediate variables. The analysis determined the classical von Karman and Townsend-Perry constants from the intermediate-scaled log-law constants.
JOURNAL OF FLUID MECHANICS
(2021)
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
Mechanics
G. G. Rooney
Summary: Dynamical constraints on the wall layer in turbulent pipe flow result in a narrow peak in the streamwise component of the turbulent Lamb vector near the wall, and a scaling relationship between the wall layer depth and the depth of the viscous sublayer. An approximation of the Lamb vector distribution, which is equivalent to the gradient of Reynolds stress, is proposed. Integration of the equation for streamwise mean flow allows for an expression of the velocity profile in the wall layer.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Aerospace
Yuma Iwamoto, Susumu Teramoto, Koji Okamoto
Summary: In this study, a harmonic balanced Large-Eddy Simulation (HB-LES) method is proposed for the efficient and accurate simulation of slowly oscillating turbulent flows. The method combines short-time LES and the harmonic balance method to compute the periodic flow and turbulent fluctuations. The HB-LES is shown to improve computational efficiency by approximately 10 times, while maintaining good agreement with experimental results and conventional LES.
Article
Mechanics
H. Jane Bae, A. Lozano-Duran, Beverley J. McKeon
Summary: The study investigates the nonlinear mechanism in the self-sustaining process of wall-bounded turbulence using resolvent analysis, identifying that removing the principal forcing mode of the fundamental wavenumber can inhibit turbulence. The contributions to the principal forcing mode come from a limited set of wavenumber interactions.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Ian Jacobi, Daniel Chung, Subrahmanyam Duvvuri, Beverley J. McKeon
Summary: This study presents a framework for predicting the interactions between motion and stress fluctuations in wall turbulence, derived from approximations to the Navier-Stokes equations. The model predictions are found to be consistent with observations, suggesting an effective approach for predicting the relationship between different-scale motions and stresses in wall turbulence.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Angeliki Laskari, Beverley J. McKeon
Summary: This study investigates the temporal behavior of the probability density function of streamwise velocity using time-resolved particle image velocimetry data, revealing the connection between these features and the change in the number of momentum zones in the flow over time. The use of limited and extended resolvent models helps in understanding the underlying velocity structures and their phase characteristics, reproducing many experimentally identified features.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Benjamin Herrmann, Peter J. Baddoo, Richard Semaan, Steven L. Brunton, Beverley J. McKeon
Summary: Resolvent analysis identifies the most responsive forcings and receptive states of a dynamic system based on its governing equations. A purely data-driven algorithm has been developed in this work to perform Resolvent analysis without recourse to the governing equations, demonstrating its applicability and data requirements. This method has potential to lower the barrier of entry to Resolvent research and applications by providing a completely equation-free and adjoint-free approach.
JOURNAL OF FLUID MECHANICS
(2021)
Editorial Material
Physics, Fluids & Plasmas
Beverley McKeon, Eric Lauga
PHYSICAL REVIEW FLUIDS
(2021)
Article
Mechanics
Benedikt Barthel, Xiaojue Zhu, Beverley McKeon
Summary: An optimization-based method is presented for efficiently calculating accurate nonlinear models of Taylor vortex flow. The method models Taylor vortex solutions by treating nonlinearity as a triadic constraint, and uses low-rank linear dynamics to calculate an efficient basis. The study finds that as the Reynolds number increases, the flow undergoes a fundamental transition from a classical weakly nonlinear regime to a fully nonlinear regime.
JOURNAL OF FLUID MECHANICS
(2021)
Editorial Material
Physics, Fluids & Plasmas
Eric Lauga, Beverley McKeon
PHYSICAL REVIEW FLUIDS
(2022)
Article
Physics, Fluids & Plasmas
Theresa Saxton-Fox, Adrian Lozano-Duran, Beverley J. McKeon
Summary: This study investigates the spatial organization of small scales around large-scale coherent structures in a flat plate turbulent boundary layer using a conditional-averaging technique applied to experimental and computational data. Two scenarios are identified for the organization of the small scales: amplitude variation and height variation. Small scales that are energetic at the center of the large-scale structure primarily show evidence of height variation, while small scales that are energetic far from the center primarily show evidence of amplitude variation.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Physics, Fluids & Plasmas
Benedikt Barthel, Salvador Gomez, Beverley J. McKeon
Summary: In this study, an inverse-free definition of the resolvent basis is proposed based on a constrained variational problem, which provides a straightforward approach to approximate the resolvent modes of complex flows. The method avoids matrix inversions and only requires the spectral decomposition of a significantly reduced matrix size. The advantages and cost-saving potential of the proposed method are demonstrated through three examples.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Multidisciplinary Sciences
Peter J. Baddoo, Benjamin Herrmann, Beverley J. McKeon, Steven L. Brunton
Summary: Research in modern data-driven dynamical systems tackles the challenges of high dimensionality, unknown dynamics, and nonlinearity. This work presents a kernel method for learning interpretable data-driven models for high-dimensional, nonlinear systems. The method efficiently handles high-dimensional data and incorporates partial knowledge of system physics.
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
(2022)
Article
Physics, Fluids & Plasmas
Angeliki Laskari, Charitha M. de Silva, Nicholas Hutchins, Beverley J. McKeon
Summary: This paper examines the robustness of the probability density function of the instantaneous streamwise velocity in extracting information on uniform momentum zones in wall-bounded flows. Through comparisons of experimental and model data sets, it highlights the consistency among different input data tested and provides important performance indicators for UMZ modeling.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Mechanics
Azadeh Jafari, Beverley J. McKeon, Maziar Arjomandi
Summary: The potential of frequency-tuned surfaces as a passive control strategy for reducing drag in wall-bounded turbulent flows is investigated using resolvent analysis. It is shown that wall impedance can suppress the modes resembling the near-wall cycle and the very-large-scale motions and the Reynolds stress contribution of these modes. Furthermore, a wall with only shear-driven impedance is found to suppress turbulent structures over a wider range in spectral space, leading to an overall turbulent drag reduction.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Multidisciplinary Sciences
Peter J. J. Baddoo, Benjamin Herrmann, BeverleyJ. J. McKeon, J. Nathan Kutz, Steven L. L. Brunton
Summary: In this work, the integration of physical principles into the dynamic mode decomposition (DMD) is demonstrated. A physics-informed DMD (piDMD) optimization is proposed to restrict the models to a matrix manifold that respects the physical structure of the system. Several closed-form solutions and efficient algorithms for the corresponding piDMD optimizations are derived based on fundamental physical principles. The piDMD models outperform standard DMD algorithms in various applications, showing advantages in spectral identification, state prediction, and estimation.
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
(2023)
Article
Physics, Fluids & Plasmas
Rahul Arun, H. Jane Bae, Beverley J. McKeon
Summary: We develop a framework for efficiently reconstructing turbulent velocity fluctuations from limited sensor measurements in real time. Linear estimators are computed using flow statistics from training data, and their performance is evaluated with testing data. The framework uses different estimators based on the availability of training data and incorporates blockwise inversion and temporal sliding discrete Fourier transform for accurate and efficient computation and streaming reconstruction.
PHYSICAL REVIEW FLUIDS
(2023)
Review
Physics, Applied
Ricardo Vinuesa, Steven L. Brunton, Beverley J. McKeon
Summary: Recent advances in machine learning have significantly impacted the field of experimental fluid mechanics. This Perspective article focuses on the application of machine learning in improving measurement techniques, experimental design, and real-time estimation and control, discussing success cases, challenges, limitations, and potential new developments.
NATURE REVIEWS PHYSICS
(2023)
