217 citations · 868 across the 46 of their papers we have counts for
48 papers
Beyond Score Accuracy: Examining the Diagnostic Quality of LLM-Generated Structured Assessment in Higher Education
Xi Zhao, Xinyue Jiao, Zhen Xu
As Large Language Models (LLMs) are increasingly adopted for automated grading and feedback in higher education, their structured outputs, including multi-dimensional rubric scores…
Assimilation of wall-pressure measurements in direct numerical simulations of high-speed flow over a cone-flare geometry
Pierluigi Morra, Brett Tillman, Stuart Laurence +1
Ensemble-variational (EnVar) assimilation of wall-pressure measurements in direct numerical simulations of Mach 6 flow over a cone-flare is performed. The experimental data include…
Latent-space variational data assimilation in two-dimensional turbulence
Andrew Cleary, Qi Wang, Tamer A. Zaki
Starting from limited measurements of a turbulent flow, data assimilation (DA) attempts to estimate all the spatio-temporal scales of motion. Success is dependent on whether the sy…
Lighthill's mechanism and vorticity cascade in the logarithmic layer of wall turbulence
Samvit Kumar, Simon Toedtli, Tamer A. Zaki +1
We investigate Lighthill's proposed turbulent mechanism for near-wall concentration of spanwise vorticity by calculating mean flows conditioned on motion away from or toward the wa…
Vorticity dynamics and drag for flows over a sphere and a prolate spheroid
Yifan Du, Tamer A. Zaki
The connection between the drag and vorticity dynamics for viscous flow over a bluff body is explored using the Josephson-Anderson (J-A) relation for classical fluids. The instanta…
Accelerating Hamiltonian Monte Carlo for Bayesian Inference in Neural Networks and Neural Operators
Ponkrshnan Thiagarajan, Tamer A. Zaki, Michael D. Shields
Hamiltonian Monte Carlo (HMC) is a powerful and accurate method to sample from the posterior distribution in Bayesian inference. However, HMC techniques are computationally demandi…
The origin of vorticity in viscous incompressible flows
Tianrui Xiang, Gregory L. Eyink, Tamer A. Zaki
In inviscid, incompressible flows, the evolution of vorticity is exactly equivalent to that of an infinitesimal material line-element, and hence vorticity can be traced forward or…
Variational data assimilation in wall turbulence: From outer observations to wall stress and pressure
Mengze Wang, Tamer A. Zaki
Estimation of near-wall turbulence in channel flow from outer observations is investigated using adjoint-variational data assimilation. We first consider fully resolved velocity da…
Multi evolutional deep neural networks (Multi-EDNN)
Hadden Kim, Tamer A. Zaki
Evolutional deep neural networks (EDNN) solve partial differential equations (PDEs) by marching the network representation of the solution fields, using the governing equations. Us…
Targeted computation of nonlocal closure operators via an adjoint-based macroscopic forcing method
Jessie Liu, Florian Schäfer, Spencer H. Bryngelson +2
Reynolds-averaged Navier--Stokes (RANS) closure must be sensitive to the flow physics, including nonlocality and anisotropy of the effective eddy viscosity. Recent approaches used…
Comparing local energy cascade rates in isotropic turbulence using structure function and filtering formulations
H. Yao, M. Schnaubelt, A. Szalay +2
Two common definitions of the spatially local rate of kinetic energy cascade at some scale in turbulent flows are (i) the cubic velocity difference term appearing in the gen…
Optimal two-dimensional roughness for transition delay in high-speed boundary layer
Reza Jahanbakhshi, Tamer A. Zaki
The influence of surface roughness on transition to turbulence in a Mach 4.5 boundary layer is studied using direct numerical simulations. Transition is initiated by the nonlinearl…
Entropy and fluctuation relations in isotropic turbulence
H. Yao, T. A. Zaki, C. Meneveau
Based on a generalized local Kolmogorov-Hill equation expressing the evolution of kinetic energy integrated over spheres of size in the inertial range of fluid turbulence, w…
Forward and inverse energy cascade and fluctuation relation in fluid turbulence adhere to Kolmogorov's refined similarity hypothesis
H. Yao, P. K. Yeung, T. A. Zaki +1
We study fluctuations of the local energy cascade rate in turbulent flows at scales () in the inertial range. According to the Kolmogorov refined similarity hypothes…
State estimation in minimal turbulent channel flow: A comparative study of 4DVar and PINN
Yifan Du, Mengze Wang, Tamer A. Zaki
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-…
Reconstructing velocity and pressure from sparse noisy particle tracks using Physics-Informed Neural Networks
Patricio Clark Di Leoni, Karuna Agarwal, Tamer Zaki +2
Volume-resolving imaging techniques are rapidly advancing progress in experimental fluid mechanics. However, reconstructing the full and structured Eulerian velocity and pressure f…
Assimilation of wall-pressure measurements in high-speed flow over a cone
David A. Buchta, Stuart J. Laurence, Tamer A. Zaki
A nonlinear ensemble-variational (EnVar) data assimilation is performed in order to estimate the unknown flow field over a slender cone at Mach-6, from isolated wall-pressure measu…
Spatio-temporal Signatures of Elasto-inertial Turbulence in Viscoelastic Planar Jets
Sami Yamani, Yashasvi Raj, Tamer A. Zaki +2
The interplay between viscoelasticity and inertia in dilute polymer solutions at high deformation rates can result in inertio-elastic instabilities. The nonlinear evolution of thes…
Origin of Enhanced Skin Friction at the Onset of Boundary-Layer Transition
Mengze Wang, Gregory L. Eyink, Tamer A. Zaki
Boundary-layer transition is accompanied by a significant increase in skin friction whose origin is rigorously explained using the stochastic Lagrangian formulation of the Navier-S…
Synchronization of turbulence in channel flow
Mengze Wang, Tamer A. Zaki
Synchronization of turbulence in channel flow is investigated using continuous data assimilation. The flow is unknown within a region of the channel. Beyond this region the velocit…
Simulations of turbulence over compliant walls
Amir Esteghamatian, Joseph Katz, Tamer A. Zaki
Direct numerical simulations of turbulent flow in a channel with one rigid and one viscoelastic wall are performed. An Eulerian-Eulerian model is adopted with a level-set approach…
Vorticity amplification in viscoelastic channel flows with long-wave surface distortions
Jacob Page, Tamer A. Zaki
Surface distortions to an otherwise planar channel flow introduce vorticity perturbations. We examine this scenario in viscoelastic fluids, and identify new mechanisms by which sig…
Ensemble-variational assimilation of statistical data in large eddy simulation
Vincent Mons, Yifan Du, Tamer A. Zaki
A non-intrusive data assimilation methodology is developed to improve the statistical predictions of large-eddy simulations (LES). The ensemble-variational (EnVar) approach aims to…
From limited observations to the state of turbulence: Fundamental difficulties of flow reconstruction
Tamer A. Zaki, Mengze Wang
Numerical simulations of turbulence provide non-intrusive access to all the resolved scales, although they often invoke idealizations that can compromise realism. In contrast, expe…