Article
Mechanics
Mateus C. Guimaraes, Fernando T. Pinho, Carlos B. da Silva
Summary: A new theory is proposed to describe the conformation state of polymer chains in free turbulent shear flows of viscoelastic fluids. The theory shows the existence of minimum and maximum solvent dissipation reduction asymptotes and four different polymer deformation regimes, based on self-similarity arguments and new scaling relations for the turbulent flux of conformation tensor. In addition, analytical solutions for the self-similar transverse profiles of the conformation tensor components are obtained. The theory is validated through excellent agreement with direct numerical simulations employing the FENE-P rheological model.
JOURNAL OF NON-NEWTONIAN FLUID MECHANICS
(2024)
Article
Mechanics
Junye Wang, Kan Wang, Meng Wang
Summary: Large-eddy simulation combined with the Ffowcs Williams-Hawkings equation was used to study noise generation by a rotor ingesting the turbulent wake of a circular cylinder. Results showed good agreement between computed sound pressure levels and experimental measurements across a wide range of frequencies. Rotor in thrusting condition produced stronger sound compared to zero thrust condition, and effects of rotor on wake turbulence were found to be relatively small.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
J. Guo, X. I. A. Yang, M. Ihme
Summary: Enhanced fluctuations, steep gradients, and intensified heat transfer are characteristic of wall-bounded turbulence at transcritical conditions. This study addresses the poorly understood structure of the thermal boundary layer under realistic density gradients and heating conditions in such flows. By performing direct numerical simulations, an improved mean temperature transformation is proposed to accurately describe the temperature field in transcritical turbulence, providing a framework for the development of models for wall-bounded transcritical turbulence.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Perry L. Johnson
Summary: This paper reimagines the theory for Large-eddy simulations (LES) and proposes a physics-inspired coarsening approach to address the shortcomings of the traditional spatial filtering theory. The approach opens up new insights even in simple wall-free flows and has the potential for extension to more complex physics, such as multiphase flows.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Byron Guerrero, Martin F. Lambert, Rey C. Chin
Summary: This study investigates the time response and transient turbulence dynamics of rapidly decelerating turbulent pipe flows. Through statistical analysis of direct numerical simulations, it is found that turbulent flows undergo four transitional stages: inertial, friction recovery, turbulence decay, and core relaxation. The FIK identity is used to understand the time response of the skin friction coefficient.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Jie Yao, Fazle Hussain
Summary: Compressible turbulent plane Couette flows with high Reynolds and Mach numbers were studied through direct numerical simulation. Various turbulence statistics were compared with incompressible flows. The skin friction coefficient decreases with Reynolds number but weakly depends on Mach number. The thermodynamic properties show significant variations with Mach number. Proper scaling transformations collapse the mean velocity profiles for compressible and incompressible cases well. Semilocal units yield a better collapse for Reynolds stress profiles compared to wall units. The length scale of near-wall coherent structures and the strength of the superstructures increase with Reynolds number. The streamwise coherence of the superstructures degrades with increasing Mach number.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
C. Chen, L. He
Summary: Recent findings on wall-bounded turbulence have led to the development of a new modelling method to capture the influence of large-scale coherent structures and scale-interaction on near-wall turbulence. This paper presents a two-scale approach to simulate this influence and validates its effectiveness.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Kai Fukami, Koji Fukagata, Kunihiko Taira
Summary: The proposed method uses supervised machine learning techniques to reconstruct high-resolution turbulent flows from coarse data, accurately reproducing flow fields and tracking temporal evolution, demonstrating strong capability and robustness.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
M. Gauding, M. Bode, Y. Brahami, E. Varea, L. Danaila
Summary: The study investigates the combined effect of internal and external intermittency on the statistical properties of temporally evolving planar turbulent jet flows at different Reynolds numbers. The analysis shows that structure functions exhibit self-preservation in both the core and shear layer of the jet, regardless of the normalization scales used. The impact of external intermittency on small-scale turbulence is demonstrated by a growing departure from self-similarity towards the flow edge.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Takuya Kawata, Takahiro Tsukahara
Summary: Interscale energy transfers in wall turbulence involve forward transfers representing streak instabilities and reversed transfers representing regeneration of streamwise vortices, as observed in direct numerical simulations.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Te-Yao Chiu, Chien-Chou Tseng, Chien-Cheng Chang, Yi-Ju Chou
Summary: This study investigated the influence of coherent structures on the aerodynamic forces acting on an aerofoil. The results showed that these structures have a significant impact on drag and lift forces, and can be identified and quantified using the SPOD algorithm and vorticity force analysis.
JOURNAL OF FLUID MECHANICS
(2023)
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
Nikolay Nikitin
Summary: A simple principle is formulated to explain and predict secondary flows in turbulent flows in straight pipes of non-circular cross-section. The study examines the relationship between wall pressure extrema and the direction of secondary flows, as well as the impact of different wall curvatures on wall pressure changes. The results indicate that secondary flows are influenced by the characteristics of the walls and properties of the fluid.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Guodan Dong, Jianhua Qin, Zhaobin Li, Xiaolei Yang
Summary: In this study, the characteristics of wind turbine wakes for three different blade designs were investigated using large-eddy simulations with the actuator surface model. The results show that the blade designs influence the velocity deficit, turbulence kinetic energy, and wake meandering. The NREL-Root design exhibits higher velocity deficit, the NREL-Tip design has higher turbulence kinetic energy in the near wake, and the NREL-Root design has higher turbulence kinetic energy in the far wake.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Aniruddhe Pradhan, Karthik Duraisamy
Summary: The main objective of this work is to develop a unified framework to assess and improve coarse-grained models of turbulence. Using a turbulent channel flow as an example, this study evaluates optimality in different limits and develops accuracy metrics for scale-resolving methods. Furthermore, a universal scaling relationship for slip velocity in wall-modeled LES is characterized, and improved slip-wall models are proposed based on insights from a priori tests.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Aerospace
Francis Lacombe, Subhajit Roy, Krishnendu Sinha, Sebastian Karl, Jean-Pierre Hickey
Summary: This study presents a semi-empirical estimate of the time-averaged thickness of a planar shock embedded in a turbulent mean flow to quantify the characteristic time and length scales for turbulence modeling. The method for calculating shock thickness is validated against direct numerical simulations and shows good accuracy across a wide range of Mach, Reynolds, and turbulent Mach numbers. The obtained ratio of characteristic shock time scale to the upstream turbulence time scale is shown to be proportional to the turbulent kinetic energy amplification through the shock, supported by direct numerical simulations.
Article
Energy & Fuels
Zheng Qiao, Yu Lv, Jean-Pierre Hickey
Summary: The study focuses on the single-phase instability of high-pressure, steady, laminar counterflow diffusion flame, with specific emphasis on the middle branch solutions characteristic of intermediary combustion states. The combustion states are influenced by operating pressure and inlet temperature, while the size and location of instability regions in the flame are determined by water vapor concentration and temperature.
Article
Engineering, Mechanical
Khaled Younes, Bradley Gibeau, Sina Ghaemi, Jean-Pierre Hickey
Summary: A method for detecting turbulent/non-turbulent interface based on fuzzy clustering of the instantaneous streamwise velocity field is proposed, overcoming the limitations of standard detection methods and showing favorable comparison with existing interface identification methods when applied to experimental wall-bounded turbulent flows.
EXPERIMENTS IN FLUIDS
(2021)
Article
Thermodynamics
Joseph Mark Epps, Jean-Pierre Hickey, John Z. Wen
Summary: A continuum-scale model for the combustion of consolidated nanothermite pellets is introduced. Sensitivity analysis reveals the relative importance of modeling parameters for combustion regimes, and a non-dimensionalization approach is proposed to establish a linear scaling between the burn rate and Peclet number, achieving consistency between numerical results and experimental data. The study identifies a transition between conduction- and advection-dominated combustion based on the transient burn rate of the nanothermite pellet combustion.
COMBUSTION AND FLAME
(2021)
Article
Mechanics
Alexander Bukva, Kevin Zhang, Nicholas Christopher, Jean-Pierre Hickey
Summary: The study evaluated Reynolds-averaged Navier-Stokes (RANS) turbulent closures for predicting turbulent boundary layers with transpiration cooling through comparison with a high-fidelity direct numerical simulation database. The RANS models performed well in qualitatively estimating velocity and thermal boundary layer evolution at low blowing ratios, but significant differences were observed at higher blowing ratios.
Article
Computer Science, Interdisciplinary Applications
Petro Junior Milan, Jean-Pierre Hickey, Xingjian Wang, Vigor Yang
Summary: A deep-learning based approach is developed for efficient evaluation of thermophysical properties in numerical simulation of complex real-fluid flows, significantly improving computational efficiency and enabling robust coupling with a flow solver. After parameter optimization, the proposed method is validated on two test problems, demonstrating effective acceleration of real-fluid property evaluation and flowfield simulation.
JOURNAL OF COMPUTATIONAL PHYSICS
(2021)
Article
Mechanics
Hamid Daryan, Fazle Hussain, Jean-Pierre Hickey
Summary: The study investigates the sound generation mechanism of initially subsonic viscous vortex reconnection at vortex Reynolds number Re = 1500. The Laplacian of kinetic energy, flexion product, enstrophy and deviation from isentropic condition contribute significantly to the acoustic source. The coiling and uncoiling of twisted vortex filaments wrapping around bridges generate significant sound due to rapid strain induced by bridge repulsion. Mutual cancellations among the acoustic source terms and symmetry breaking play important roles in sound generation. Compressibility delays the onset of reconnection events, impacting sound generation.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Joseph Mouallem, Hamid Daryan, Joshua Wawryk, Zhao Pan, Jean-Pierre Hickey
Summary: The study proposes a conceptual model for targeted particle delivery using controlled vortex ring reconnection. By causing vortex reconnection events, efficient particle transport to the desired location on the sidewalls of a ducted flow is achieved. The research demonstrates the dominant physics of the process and considerations for targeted delivery.
Article
Mechanics
Ahmed Saieed, Mustafa Mutiur Rahman, Jean-Pierre Hickey
Summary: This study investigates the effect of temperature-dependent viscosity on the preferential concentration of bidisperse particles in decaying turbulence. The results show that the liquid- and gas-like viscosity affect the clustering of particles, and this effect varies with the functional form of the temperature-dependent viscosity.
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2022)
Article
Computer Science, Interdisciplinary Applications
Jeremy C. H. Wang, Jean-Pierre Hickey
Summary: The study introduces a structurally complete approximate Riemann solver (StARS) that significantly improves the accuracy and computational requirements of finite volume codes by addressing the restoration of expansion waves. The method is valid for arbitrary thermodynamics and has comparable complexity to popular entropy fix methods. The StARS modification shows noticeable improvements in cases with large flow gradients, highlighting the complex causes and effects of entropy violations.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Engineering, Aerospace
Khaled Younes, Jean-Pierre Hickey
Summary: The scaling of near-wall mean velocity profiles in turbulent flows has been traditionally studied using various assumptions. Recent work has shown success with a quasi-equilibrium assumption, but its validity for noncanonical flows is uncertain. This study proposes an alternate transformation method based on the semilocal gradient of the velocity and a modified stress balance. The new method demonstrates improved performance, especially at supercritical pressures.
Article
Computer Science, Software Engineering
Francis Lacombe, Jean -Pierre Hickey
Summary: Krypton is an open-source framework for solving stability equations on a curvilinear coordinate system, specifically predicting laminar-to-turbulent transition under transonic conditions. It is written in Python and includes a laminar flow solver using a consistent numerical scheme for modal stability calculations. The framework has been validated and can be used as a foundation for future development in aerospace engineering, geophysics, and multiphase flows.
Review
Physics, Fluids & Plasmas
Arnav Joshi, Mustafa M. Rahman, Jean-Pierre Hickey
Summary: This paper presents a comprehensive review of passive acoustic aircraft and wake localization methods. It discusses the generation and propagation of sound, as well as the utilization of microphones and known noise sources for acoustic localization. The paper focuses on beamforming and machine learning techniques and their application in aerospace. The review brings together aeroacoustics and acoustic-based detection to advance passive acoustic localization techniques in the field.
Proceedings Paper
Computer Science, Artificial Intelligence
Sushrut Bhalla, Matthew Yao, Jean-Pierre Hickey, Mark Crowley
MACHINE LEARNING AND KNOWLEDGE DISCOVERY IN DATABASES, ECML PKDD 2019, PT III
(2020)
Article
Mechanics
Joseph Mouallem, Jean-Pierre Hickey
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2020)