@article{fowler_zaki_meneveau_2023,

title = {A multi-time-scale wall model for large-eddy simulations and applications to non-equilibrium channel flows},

author = {Mitchell Fowler and Tamer A. Zaki and Charles Meneveau},

doi = {10.1017/jfm.2023.585},

year  = {2023},

date = {2023-01-01},

journal = {Journal of Fluid Mechanics},

volume = {974},

pages = {A51},

publisher = {Cambridge University Press},

keywords = {Channel, Turbulence, Wall modeling},

pubstate = {published},

tppubtype = {article}

}

@article{yao_etal_2023,

title = {Entropy and fluctuation relations in isotropic turbulence},

author = {Hanxun Yao and Tamer A. Zaki and Charles Meneveau},

doi = {10.1017/jfm.2023.808},

year  = {2023},

date = {2023-01-01},

journal = {Journal of Fluid Mechanics},

volume = {973},

pages = {R6},

publisher = {Cambridge University Press},

keywords = {Entropy, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{du_etal_2023,

title = {State estimation in minimal turbulent channel flow: A comparative study of 4DVar and PINN},

author = {Yifan Du and Mengze Wang and Tamer A. Zaki},

url = {https://www.sciencedirect.com/science/article/pii/S0142727X22001412},

doi = {https://doi.org/10.1016/j.ijheatfluidflow.2022.109073},

issn = {0142-727X},

year  = {2023},

date = {2023-01-01},

journal = {International Journal of Heat and Fluid Flow},

volume = {99},

pages = {109073},

abstract = {The state of turbulent, minimal-channel flow is estimated from spatio-temporal sparse observations of the velocity, using both a physics-informed neural network (PINN) and adjoint-variational data assimilation (4DVar). The performance of PINN is assessed against the benchmark results from 4DVar. The PINN is efficient to implement, takes advantage of automatic differentiation to evaluate the governing equations, and does not require the development of an adjoint model. In addition, the flow evolution is expressed in terms of the network parameters which have a far smaller dimension than the predicted trajectory in state space or even just the initial condition of the flow. Provided adequate observations, network architecture and training, the PINN can yield satisfactory estimates of the flow field, both for the missing velocity data and the entirely unobserved pressure field. However, accuracy depends on the network architecture, and the dependence is not known a priori. In comparison to 4DVar estimation which becomes progressively more accurate over the observation horizon, the PINN predictions are generally less accurate and maintain the same level of errors throughout the assimilation time window. Another notable distinction is the capacity to accurately forecast the flow evolution: while the 4DVar prediction depart from the true flow state gradually and according to the Lyapunov exponent, the PINN is entirely inaccurate immediately beyond the training time horizon unless re-trained. Most importantly, while 4DVar satisfies the discrete form of the governing equations point-wise to machine precision, in PINN the equations are only satisfied in an L2 sense.},

keywords = {4DVar, Adjoint variational method, Data assimilation, Physics informed neural networks, PINN, State estimation, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{wang_Hesisan_jfm2022,

title = {What is observable from wall data in turbulent channel flow?},

author = {Qi Wang and Mengze Wang and Tamer A. Zaki},

doi = {10.1017/jfm.2022.295},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Fluid Mechanics},

volume = {941},

pages = {A48},

publisher = {Cambridge University Press},

keywords = {Channel, Data assimilation, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{wang_Synch_jfm2022,

title = {Synchronization of turbulence in channel flow},

author = {Mengze Wang and Tamer A. Zaki},

doi = {10.1017/jfm.2022.397},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Fluid Mechanics},

volume = {943},

pages = {A4},

publisher = {Cambridge University Press},

keywords = {Channel, Data assimilation, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{esteghamatian_jfm2022,

title = {Spatiotemporal characterization of turbulent channel flow with a hyperelastic compliant wall},

author = {Amir Esteghamatian and Joseph Katz and Tamer A. Zaki},

doi = {10.1017/jfm.2022.354},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Fluid Mechanics},

volume = {942},

pages = {A35},

publisher = {Cambridge University Press},

keywords = {Channel, Compliant walls, Turbulence, Viscoelastic},

pubstate = {published},

tppubtype = {article}

}

@article{wang_Stochastic_jfm2022,

title = {Origin of enhanced skin friction at the onset of boundary-layer transition},

author = {Mengze Wang and Gregory L. Eyink and Tamer A. Zaki},

doi = {10.1017/jfm.2022.296},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Fluid Mechanics},

volume = {941},

pages = {A32},

publisher = {Cambridge University Press},

keywords = {Channel, Data assimilation, Drag, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{fowler_jfm2022,

title = {A Lagrangian relaxation towards equilibrium wall model for large eddy simulation},

author = {Mitchell Fowler and Tamer A. Zaki and Charles Meneveau},

doi = {10.1017/jfm.2021.1156},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Fluid Mechanics},

volume = {934},

pages = {A44},

publisher = {Cambridge University Press},

keywords = {Channel, LES, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{mons_prf2021,

title = {Ensemble-variational assimilation of statistical data in large-eddy simulation},

author = {Vincent Mons and Yifan Du and Tamer A. Zaki},

url = {https://link.aps.org/doi/10.1103/PhysRevFluids.6.104607},

doi = {10.1103/PhysRevFluids.6.104607},

year  = {2021},

date = {2021-10-01},

journal = {Phys. Rev. Fluids},

volume = {6},

issue = {10},

pages = {104607},

publisher = {American Physical Society},

keywords = {Channel, Data assimilation, Ensemble Variational Methods, EnVar, LES, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{zaki_prf2021,

title = {From limited observations to the state of turbulence: Fundamental difficulties of flow reconstruction},

author = {Tamer A. Zaki and Mengze Wang},

url = {https://link.aps.org/doi/10.1103/PhysRevFluids.6.100501},

doi = {10.1103/PhysRevFluids.6.100501},

year  = {2021},

date = {2021-10-01},

journal = {Phys. Rev. Fluids},

volume = {6},

issue = {10},

pages = {100501},

publisher = {American Physical Society},

keywords = {Data assimilation, Ensemble Variational Methods, EnVar, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{clark_di_leoni_jfm2021,

title = {Two-point stress--strain-rate correlation structure and non-local eddy viscosity in turbulent flows},

author = {Patricio Clark Di Leoni and Tamer A. Zaki and George Karniadakis and Charles Meneveau},

doi = {10.1017/jfm.2020.977},

year  = {2021},

date = {2021-01-01},

journal = {Journal of Fluid Mechanics},

volume = {914},

pages = {A6},

publisher = {Cambridge University Press},

keywords = {LES, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{you_jfm2021,

title = {Concave-wall turbulent boundary layers without and with free-stream turbulence},

author = {Jiho You and David A. Buchta and Tamer A. Zaki},

doi = {10.1017/jfm.2021.12},

year  = {2021},

date = {2021-01-01},

journal = {Journal of Fluid Mechanics},

volume = {915},

pages = {A4},

publisher = {Cambridge University Press},

keywords = {Boundary layers, Curvature, Freestream Turbulence, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{wang_jfm2021,

title = {State estimation in turbulent channel flow from limited observations},

author = {Mengze Wang and Tamer A. Zaki},

doi = {10.1017/jfm.2021.268},

year  = {2021},

date = {2021-01-01},

journal = {Journal of Fluid Mechanics},

volume = {917},

pages = {A9},

publisher = {Cambridge University Press},

keywords = {Adjoint, Channel, Data assimilation, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{esteghamatian_jfm2021,

title = {The dynamics of settling particles in vertical channel flows: gravity, lift and particle clusters},

author = {Amir Esteghamatian and Tamer A. Zaki},

doi = {10.1017/jfm.2021.304},

year  = {2021},

date = {2021-01-01},

journal = {Journal of Fluid Mechanics},

volume = {918},

pages = {A33},

publisher = {Cambridge University Press},

keywords = {Channel, Particles, Turbulence, Viscoelastic},

pubstate = {published},

tppubtype = {article}

}

@article{Wu3461,

title = {High-Reynolds-number fractal signature of nascent turbulence during transition},

author = {Zhao Wu and Tamer A Zaki and Charles Meneveau},

url = {https://www.pnas.org/content/117/7/3461},

doi = {10.1073/pnas.1916636117},

issn = {0027-8424},

year  = {2020},

date = {2020-01-01},

journal = {Proceedings of the National Academy of Sciences},

volume = {117},

number = {7},

pages = {3461--3468},

publisher = {National Academy of Sciences},

keywords = {Bypass, Conditional Sampling, Freestream Turbulence, Machine Learning, Spots, T/NT interface, Transition, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{eyink_gupta_zaki_2020b,

title = {Stochastic Lagrangian dynamics of vorticity. Part 2. Application to near-wall channel-flow turbulence},

author = {Gregory L Eyink and Akshat Gupta and Tamer A Zaki},

doi = {10.1017/jfm.2020.492},

year  = {2020},

date = {2020-01-01},

journal = {Journal of Fluid Mechanics},

volume = {901},

pages = {A3},

publisher = {Cambridge University Press},

keywords = {Channel, Drag, Navier-Stokes, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{eyink_gupta_zaki_2020,

title = {Stochastic Lagrangian dynamics of vorticity. Part 1. General theory for viscous, incompressible fluids},

author = {Gregory L Eyink and Akshat Gupta and Tamer A Zaki},

doi = {10.1017/jfm.2020.491},

year  = {2020},

date = {2020-01-01},

journal = {Journal of Fluid Mechanics},

volume = {901},

pages = {A2},

publisher = {Cambridge University Press},

keywords = {Channel, Drag, Navier-Stokes, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{you_ftc2020,

title = {Turbulent Heat-Transfer Enhancement in Boundary Layers Exposed to Free-Stream Turbulence},

author = {Jiho You and Tamer A Zaki},

url = {https://doi.org/10.1007/s10494-019-00071-7},

doi = {10.1007/s10494-019-00071-7},

isbn = {1573-1987},

year  = {2020},

date = {2020-01-01},

journal = {Flow, Turbulence and Combustion},

abstract = {Direct numerical simulations (DNS) are performed to study the effect of free-stream vortical forcing on a thermal turbulent boundary layer. In presence of external perturbations, the heat-transfer rate from the wall is increased relative to the unforced case. An explanation is provided, and starts from the free-stream forcing which enhances the Reynolds stresses inside the boundary layer, and in particular the wall-normal component. As a result, the wall-normal heat flux is also increased, which has the dual effect of distorting the base temperature profile and enhancing the production of scalar variance; both contribute to the increase in the wall heat-transfer rate. In addition, the flow sustains higher thermal fluctuations, even though the free-stream forcing is only vortical, and not thermal. These changes are accompanied by modification of the spectra of the thermal field in the outer region of the boundary layer, where large-scale thermal structures are formed in response to the large-scale velocity motions. In the near-wall region, the thermal structures are modulated by the outer hydrodynamic field and are strengthened relative to the unforced flow.},

keywords = {Scalar, T/NT interface, Turbulence, Very-large-scale Motion},

pubstate = {published},

tppubtype = {article}

}

@article{mons_jcp2019,

title = {Kriging-enhanced ensemble variational data assimilation for scalar-source identification in turbulent environments},

author = {Vincent Mons and Qi Wang and Tamer A Zaki},

url = {http://www.sciencedirect.com/science/article/pii/S0021999119305406},

doi = {https://doi.org/10.1016/j.jcp.2019.07.054},

issn = {0021-9991},

year  = {2019},

date = {2019-01-01},

journal = {Journal of Computational Physics},

volume = {398},

pages = {108856},

abstract = {Various ensemble-based variational (EnVar) data assimilation (DA) techniques are developed to reconstruct the spatial distribution of a scalar source in a turbulent channel flow resolved by direct numerical simulation (DNS). In order to decrease the computational cost of the DA procedure and improve its performance, Kriging-based interpolation is combined with EnVar DA, which enables the consideration of relatively large ensembles with moderate computational resources. The performance of the proposed Kriging-EnVar (KEnVar) DA scheme is assessed and favorably compared to that of standard EnVar and adjoint-based variational DA in various scenarios. Sparse regularization is implemented in the framework of EnVar DA in order to better tackle the case of concentrated scalar emissions. The problem of optimal sensor placement is also addressed, and it is shown that significant improvement in the quality of the reconstructed source can be obtained without supplementary computational cost once the ensemble required by the DA procedure is formed.},

keywords = {Channel, Data assimilation, Optimization, Scalar dispersion, Sensor placement, Source identification, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{wu_prf2019,

title = {Application of a self-organizing map to identify the turbulent-boundary-layer interface in a transitional flow},

author = {Zhao Wu and Jin Lee and Charles Meneveau and Tamer Zaki},

url = {https://link.aps.org/doi/10.1103/PhysRevFluids.4.023902},

doi = {10.1103/PhysRevFluids.4.023902},

year  = {2019},

date = {2019-01-01},

journal = {Phys. Rev. Fluids},

volume = {4},

pages = {023902},

publisher = {American Physical Society},

keywords = {Bypass, Machine Learning, Spots, T/NT interface, Transition, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{you_jfm2019,

title = {Conditional statistics and flow structures in turbulent boundary layers buffeted by free-stream disturbances},

author = {Jiho You and Tamer A Zaki},

doi = {10.1017/jfm.2019.104},

year  = {2019},

date = {2019-01-01},

journal = {Journal of Fluid Mechanics},

volume = {866},

pages = {526--566},

publisher = {Cambridge University Press},

keywords = {T/NT interface, Turbulence, Very-large-scale Motion},

pubstate = {published},

tppubtype = {article}

}

@article{ismail_ijhff2018,

title = {The effect of cube-roughened walls on the response of rough-to-smooth (RTS) turbulent channel flows},

author = {U Ismail and T A Zaki and P A Durbin},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Ismail_IJHFF_2018.pdf},

year  = {2018},

date = {2018-01-01},

journal = {International Journal of Heat and Fluid Flow},

volume = {72},

pages = {174-185},

keywords = {Channel, Roughness, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{ismail_jfm2018,

title = {Simulations of rib-roughened rough-to-smooth turbulent channel flows},

author = {U Ismail and T A Zaki and P A Durbin},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Ismail_JFM_2018.pdf},

year  = {2018},

date = {2018-01-01},

journal = {Journal of Fluid Mechanics},

volume = {843},

pages = {419-449},

keywords = {Channel, Roughness, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{lee_jfm2017b,

title = {Signature of large-scale motions on turbulent/non-turbulent interface in boundary layers},

author = {Jin Lee and Hyung Jin Sung and Tamer A Zaki},

doi = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Lee_JFM_2017.pdf},

year  = {2017},

date = {2017-01-01},

journal = {Journal of Fluid Mechanics},

volume = {819},

pages = {165-187},

keywords = {T/NT interface, Turbulence, Very-large-scale Motion},

pubstate = {published},

tppubtype = {article}

}

@article{hwang_jfm2016,

title = {Inner-outer interactions of large-scale structures in turbulent channel flow},

author = {Jinyul Hwang and Jin Lee and Hyung Jin Sung and Tamer A Zaki},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Hwang_JFM_2016.pdf},

year  = {2016},

date = {2016-01-01},

journal = {J. Fluid Mechanics},

volume = {790},

pages = {128-157},

keywords = {Channel, Conditional Sampling, Turbulence, Very-large-scale Motion},

pubstate = {published},

tppubtype = {article}

}

@article{cerizza_ftc2016,

title = {Reconstruction of scalar source intensity based on sensor signal in turbulent channel flow},

author = {Davide Cerizza and W Sekiguchi and T Tsukahara and Tamer A Zaki and Yosuke Hasegawa},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Cerizza_FTC_2016.pdf},

year  = {2016},

date = {2016-01-01},

journal = {Flow, Turbulence & Combustion},

volume = {97},

number = {4},

pages = {1211--1233},

keywords = {Adjoint, Dispersion, Infotaxis, Optimization, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{lee_ftc2015,

title = {Effect of Reynolds number on turbulent drag reduction by superhydrophobic surface textures},

author = {Jin Lee and Thomas O Jelly and Tamer A Zaki},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Lee_FTC_2015.pdf},

year  = {2015},

date = {2015-01-01},

journal = {Flow, Turbulence & Combustion},

volume = {95},

pages = {277 - 300},

keywords = {Channel, Conditional Sampling, Drag, Streaks, Superhydrophobic, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{jelly_pof2014,

title = {Turbulence and skin-friction modification in channel flow with streamwise-aligned superhydrophobic surface textures},

author = {Thomas O Jelly and Seo Yoon Jung and Tamer A Zaki},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Jelly_PoF_2014.pdf},

year  = {2014},

date = {2014-01-01},

journal = {Physics of Fluids},

volume = {26},

number = {095102},

keywords = {Channel, Drag, Superhydrophobic, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{lee_ijhff2014,

title = {Turbulent thermal boundary layers with temperature-dependent viscosity},

author = {Jin Lee and Seo Yoon Jung and Hyung Jin Sung and Tamer A Zaki},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Lee_IJHFF_2014.pdf},

year  = {2014},

date = {2014-01-01},

journal = {International Journal of Heat and Fluid Flow},

keywords = {Drag, Scalar, Shear, Stratification, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{cheung_jfm2014,

title = {An exact representation of the nonlinear triad interaction terms in spectral space},

author = {Lawrence C Cheung and Tamer A Zaki},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Cheung_JFM_2014.pdf},

year  = {2014},

date = {2014-01-01},

journal = {Journal of Fluid Mechanics},

volume = {748},

pages = {175-188},

keywords = {Triad, Turbulence},

pubstate = {published},

tppubtype = {article}

}

@article{lee_jfm2013,

title = {Effect of wall heating on turbulent boundary layers with temperature-dependent viscosity},

author = {Jin Lee and Seo Yoon Jung and Hyung Jin Sung and Tamer A Zaki},

url = {https://engineering.jhu.edu/zaki/wp-content/uploads/2018/12/Lee_JFM_2013.pdf},

year  = {2013},

date = {2013-01-01},

journal = {Journal of Fluid Mechanics},

volume = {726},

pages = {196-225},

keywords = {Drag, Shear, Stratification, Turbulence},

pubstate = {published},

tppubtype = {article}

}