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
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
Christoph Wenzel, Tobias Gibis, Markus Kloker, Ulrich Rist
Summary: This study quantitatively evaluates the Reynolds analogy factor for self-similar turbulent boundary layers with pressure gradients using direct numerical simulation. The factor is found to increase for adverse-pressure-gradient cases and decrease for favourable-pressure-gradient cases. Mach number has a small influence, and no dependency on Reynolds number was observed. The effects of pressure gradients can be approximated by an analytical relation derived by So in incompressible flow.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
K. Matsuno, S. K. Lele
Summary: The study reveals that at high Mach numbers, the spatial scales of eddying motions in mixing layers progressively decrease, forming independent layers of eddying motions, thereby reducing the effective velocity scale for turbulent motions and suppressing Reynolds stresses, turbulent kinetic energy production and dissipation, and the growth rate of mixing-layer thickness.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Mustafa Z. Yousif, Meng Zhang, Linqi Yu, Ricardo Vinuesa, HeeChang Lim
Summary: This study proposes a new deep-learning-based method for generating turbulent inflow conditions in spatially developing turbulent boundary layer (TBL) simulations. The model combines a transformer and a multiscale-enhanced super-resolution generative adversarial network to predict velocity fields of the TBL at different planes. The model shows remarkable accuracy in predicting velocity fields and reproducing turbulence statistics. Furthermore, it demonstrates the effectiveness of using transformer-based models and generative adversarial networks for various turbulence-related problems.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Yukio Kaneda, Yoshinobu Yamamoto
Summary: This paper extends Kolmogorov's local similarity hypotheses to include the influence of mean shear on the statistics of fluctuating velocity. The moments of the velocity gradients are determined by the local turbulent energy dissipation rate, kinematic viscosity, and parameter gamma. The anisotropy of moments decreases approximately in proportion to gamma when gamma is small in an appropriate sense.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Michele Cogo, Francesco Salvadore, Francesco Picano, Matteo Bernardini
Summary: The structure of high-speed zero-pressure-gradient turbulent boundary layers was studied using direct numerical simulation of the Navier-Stokes equations up to high Reynolds numbers, revealing the consequences in supersonic and hypersonic conditions. Instantaneous fields showed elongated strips of uniform velocity and temperature with clear associations between different streaks.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Xiaoning Wang, Jianchun Wang, Shiyi Chen
Summary: This study investigates the effects of compressibility on the statistics and coherent structures of a temporally developing mixing layer through numerical simulations. The results show that as the convective Mach number increases, the streamwise dissipation becomes more effective in suppressing turbulent kinetic energy. At low convective Mach numbers, the mixing layer is accompanied by spanwise Kelvin-Helmholtz rollers, while at higher convective Mach numbers, large-scale high- and low-speed structures dominate. The study also reveals a correlation between high-shearing motions on top of low-speed structures and the clustering of small-scale vortical structures.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jiho You, David A. Buchta, Tamer A. Zaki
Summary: Direct numerical simulations were conducted to investigate turbulent boundary layers over a concave wall with and without free-stream turbulence. The presence of free-stream turbulence reduced reverse flow probability, increased skin friction, and promoted the amplification of Gortler structures. Additionally, coherent roll motions in the forced flow facilitated mixing of free-stream and boundary-layer fluids.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jonathan Neuhauser, Kay Schaefer, Davide Gatti, Bettina Frohnapfel
Summary: Heterogeneous roughness in the form of streamwise aligned strips can generate large scale secondary motions under turbulent flow conditions. We propose a simple roughness model that can capture the features of turbulent secondary flow without impacting the laminar base flow. The model shows good agreement with experimental data in terms of the secondary flow topology.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Akanksha Baranwal, Diego A. Donzis, Rodney D. W. Bowersox
Summary: This study investigates the effects of compressibility on the near-wall asymptotic behavior of turbulent fluxes using a large direct numerical simulation (DNS) database, finding that the behavior of compressible turbulent flow near walls differs from incompressible flow even when mean density variations are considered. As Mach number increases, turbulent fluxes containing wall-normal components exhibit a decrease in slope due to increased dilatation effects, with Ity approaching its high Mach number asymptote at lower Mach numbers than other fluxes.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Alessandro Ceci, Andrea Palumbo, Johan Larsson, Sergio Pirozzoli
Summary: This study investigates the influence of turbulence inflow generation on high-speed turbulent boundary layers through direct numerical simulations (DNS). Two main types of inflow conditions are considered and compared. DNS with very long streamwise domains are performed to provide reliable data. Simulations with shorter domains are then conducted and compared with benchmark data, revealing significant deviations and dependency on inflow turbulence seeding.
THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS
(2022)
Article
Thermodynamics
L. Laguarda, S. Hickel, F. F. J. Schrijer, B. W. van Oudheusden
Summary: Wall-resolved large-eddy simulations were used to investigate the Reynolds number effects in supersonic turbulent boundary layers at Mach 2.0. The study covered a wide range of friction Reynolds numbers and identified trends in various statistics and scaling laws. The size and topology of turbulent structures in the boundary layer were examined, with a focus on the outer-layer motions at high Reynolds numbers. The study also assessed the influence of outer-layer structures on near-wall turbulence and the sensitivity of uniform momentum regions to compressibility.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Mechanics
Mengze Wang, Tamer A. Zaki
Summary: Estimation of the initial state of turbulent channel flow from limited data is investigated using an adjoint-variational approach. The study demonstrates the robustness of the algorithm to observation noise and evaluates the impact of the spatiotemporal density of the data on estimation quality. Results show a resolution threshold for successful reconstruction and highlight the difficulty of reconstructing wall-detached motions from wall data.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
J. C. Klewicki
Summary: High resolution direct numerical simulation data are used to investigate the similarity solutions for mean velocity and Reynolds shear stress in turbulent channel flow. The analysis yields an invariant form of the mean momentum equation valid over a significant portion of the flow domain. The results provide insights into the development of wall-flow models and support conjectures regarding the behavior of similarity parameters at large Reynolds numbers.
JOURNAL OF FLUID MECHANICS
(2021)
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
Multidisciplinary Sciences
H. Jane Bae, Petros Koumoutsakos
Summary: Researchers propose a multi-agent reinforcement learning approach to discover wall models for large-eddy simulations, solving the challenge of capturing near-wall dynamics in turbulent flow simulations.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Fluids & Plasmas
Wybe Rozema, H. Jane Bae, Roel W. C. P. Verstappen
Summary: This paper presents a local dynamic model for large-eddy simulation (LES) to address the singularity issue of the widely used dynamic Smagorinsky model (DSM). By replacing the resolved rate-of-strain tensors with the resolved velocity gradient tensor, the model improves the local applicability. Simulation results demonstrate that the model provides better stability and lower computational complexity compared to the local DSM.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Computer Science, Interdisciplinary Applications
Suhas S. Jain, Parviz Moin
Summary: This study utilizes the conservative diffuse-interface method to simulate compressible two-phase flows and proposes discrete consistency conditions for numerical fluxes to ensure conservation of kinetic energy and entropy. The stability of the proposed method is verified in canonical test cases, as well as in flows with droplets.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Editorial Material
Mechanics
Howard A. Stone, Parviz Moin
ANNUAL REVIEW OF FLUID MECHANICS
(2023)
Article
Computer Science, Interdisciplinary Applications
Suhas S. Jain, Michael C. Adler, Jacob R. West, Ali Mani, Parviz Moin, Sanjiva K. Lele
Summary: This work describes three diffuse-interface methods for simulating immiscible, compressible multiphase fluid flows and elastic-plastic deformation in solids. The methods include localized artificial diffusivity, gradient-form, and divergence-form approaches. The primary objective is to compare these methods in terms of their ability to maintain interface thickness, conserve mass, momentum, and energy, and accurately represent interface shape over time. The work also extends these methods to model interfaces between solid materials with strength.
JOURNAL OF COMPUTATIONAL PHYSICS
(2023)
Article
Physics, Fluids & Plasmas
Hanul Hwang, Dokyun Kim, Parviz Moin
Summary: This paper is associated with a winner video of the 2021 American Physical Society's Division of Fluid Dynamics (DFD) Gallery of Fluid Motion Award. The original video can be viewed online at the Gallery of Fluid Motion website.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Mechanics
Adrian Lozano-Duran, H. Jane Bae
Summary: A wall model for large-eddy simulation (LES) is proposed using artificial neural networks to predict wall shear stress in complex flow scenarios. The model identifies the contribution of each building block in the flow and estimates the wall shear stress using a combination of these flow blocks. The model is validated through experiments, showing its accuracy in predicting wall shear stress.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Marios-Andreas Nikolaidis, Petros J. Ioannou, Brian F. Farrell, Adrian Lozano-Duran
Summary: Turbulence in restricted nonlinear (RNL) dynamics is compared with direct numerical simulations (DNS) of Poiseuille turbulence at a specified Reynolds number. The structures in RNL dynamics are obtained through proper orthogonal decomposition (POD) analysis of the flow partition, revealing dominant roll-streak harmonic modes in both DNS and RNL dynamics. Additionally, POD analysis of the fluctuations in DNS and RNL dynamics reveals similar complex structures consisting of oblique waves collocated with the streaks. This correspondence suggests that the self-sustaining mechanism in DNS and RNL dynamics is essentially the same, associated with optimal perturbation growth on the streaks as predicted by a stochastic turbulence model (STM).
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Aurelien Vadrot, Xiang I. A. Yang, H. Jane Bae, Mahdi Abkar
Summary: This paper focuses on the use of reinforcement learning (RL) for near-wall turbulence modeling. A new RL wall model (WM) called VYBA23 is developed, which uses agents dispersed in the flow near the wall. The model is trained on a single Reynolds number and does not rely on high-fidelity data. The results show potential for developing RLWMs that can recover physical laws and for extending this type of ML models to more complex flows in the future.
Article
Physics, Fluids & Plasmas
Shuisheng He, Adrian Lozano-Duran, Jundi He, Minjeong Cho
Summary: In this study, a temporally developing three-dimensional turbulent boundary layer is investigated using direct numerical simulation. The flow is initiated by subjecting a statistically stationary turbulent channel flow to a constant transverse pressure gradient while maintaining the streamwise pressure gradient unchanged. It is shown that the nonequilibrium three-dimensional boundary layer can be described as a turbulent-turbulent transition characterized by the development of a laminar boundary layer in an initial turbulent environment followed by a transition to turbulence. The transient developments of both the mean flow and turbulence are understood by relating them to the process of transition. The rotation of streaks and the damping effect of the spanwise boundary layer work together to suppress the streamwise and wall-normal turbulence, causing the overall turbulent kinetic energy and the structure parameter to decrease.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Mechanics
Alvaro Martinez-Sanchez, Esteban Lopez, Soledad Le Clainche, Adrian Lozano-Duran, Ankit Srivastava, Ricardo Vinuesa
Summary: The aim of this work is to analyze the formation mechanisms of large-scale coherent structures in the flow around a wall-mounted square cylinder and assess the causal relations between different flow modes. Conditional transfer entropy is used to identify the causal relations and understand the origins and evolution of different flow phenomena. The study reveals that vortex-breaker modes are the most causal modes, while no significant causal relationships were found for vortex-generator modes.
JOURNAL OF FLUID MECHANICS
(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)
Article
Physics, Multidisciplinary
Adrian Lozano-Duran, Gonzalo Arranz
Summary: This study formulates the problems of causality, modeling, and control for chaotic, high-dimensional dynamical systems in the language of information theory, with the Shannon entropy as the central quantity of interest. Causality is quantified by the information flux among the variables, reduced-order modeling aims at preserving relevant information, and control theory envisions the sensor-actuator as reducing unknown information of the state. The study applies this framework to address problems in turbulence, including energy transfer causality, subgrid-scale modeling, and flow control for drag reduction.
PHYSICAL REVIEW RESEARCH
(2022)