Tim Colonius
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View article: Normality-based analysis of multiscale velocity gradients and energy transfer in direct and large-eddy simulations of isotropic turbulence
Normality-based analysis of multiscale velocity gradients and energy transfer in direct and large-eddy simulations of isotropic turbulence Open
Symmetry-based analyses of multiscale velocity gradients highlight that strain self-amplification (SS) and vortex stretching (VS) drive forward energy transfer in turbulent flows. By contrast, a strain–vorticity covariance mechanism produc…
View article: Nonlinear dynamics of vortex pairing in transitional jets
Nonlinear dynamics of vortex pairing in transitional jets Open
This study investigates the onset of linear instabilities and their later nonlinear interactions in the shear layer of an initially laminar jet using high-fidelity simulations. We present a quantitative analysis of the vortex-pairing pheno…
View article: Resolvent4py: A parallel Python package for analysis, model reduction and control of large-scale linear systems
Resolvent4py: A parallel Python package for analysis, model reduction and control of large-scale linear systems Open
In this paper, we present resolvent4py, a parallel Python package for the analysis, model reduction and control of large-scale linear systems with millions or billions of degrees of freedom. This package provides the user with a friendly P…
View article: Resolvent4py: a parallel Python package for analysis, model reduction and control of large-scale linear systems
Resolvent4py: a parallel Python package for analysis, model reduction and control of large-scale linear systems Open
In this paper, we present resolvent4py, a parallel Python package for the analysis, model reduction and control of large-scale linear systems with millions or billions of degrees of freedom. This package provides the user with a friendly P…
View article: Greedy recursion parameter selection for the One-Way Navier-Stokes (OWNS) equations
Greedy recursion parameter selection for the One-Way Navier-Stokes (OWNS) equations Open
The One-Way Navier-Stokes (OWNS) equations use recursive filtering to construct efficient, well-posed one-way approximations to linear hyperbolic systems. The recursion parameters are critical to the accuracy and stability of the method, a…
View article: Numerical methods for multiphase flows
Numerical methods for multiphase flows Open
View article: Spectral proper orthogonal decomposition of rapid snapshot pairs sampled at sub-Nyquist intervals
Spectral proper orthogonal decomposition of rapid snapshot pairs sampled at sub-Nyquist intervals Open
Modal decomposition methods are important for characterizing the low-dimensional dynamics of complex systems, including turbulent flows. Different methods have varying data requirements and produce modes with different properties. Spectral…
View article: Resolvent4py: A Parallel Python Package for Analysis, Model Reduction and Control of Large-Scale Linear Systems
Resolvent4py: A Parallel Python Package for Analysis, Model Reduction and Control of Large-Scale Linear Systems Open
View article: Velocity gradient partitioning in turbulent flows
Velocity gradient partitioning in turbulent flows Open
The velocity gradient tensor can be decomposed into normal straining, pure shearing and rigid rotation tensors, each with distinct symmetry and normality properties. We partition the strength of turbulent velocity gradients based on the re…
View article: Superresolution and analysis of three-dimensional velocity fields of underexpanded jets in different screech modes
Superresolution and analysis of three-dimensional velocity fields of underexpanded jets in different screech modes Open
Time-resolved (TR), three-dimensional (3D) velocity fields of screeching, underexpanded jets are estimated using non-time-resolved particle image velocimetry and simultaneous TR microphone measurements. Specifically, we aim to reconstruct …
View article: Boundary layer stability analysis using the nonlinear One-Way Navier-Stokes approach
Boundary layer stability analysis using the nonlinear One-Way Navier-Stokes approach Open
We extend the One-Way Navier Stokes (OWNS) approach to support nonlinear interactions between waves of different frequencies, which will enable nonlinear analysis of instability and transition. In OWNS, the linearized Navier-Stokes equatio…
View article: Velocity gradient partitioning in turbulent flows
Velocity gradient partitioning in turbulent flows Open
The velocity gradient tensor can be decomposed into normal straining, pure shearing and rigid rotation tensors, each with distinct symmetry and normality properties. We partition the strength of turbulent velocity gradients based on the re…
View article: Coherence Decay in Turbulent Jets by Stochastic Modelling Under Location Uncertanty
Coherence Decay in Turbulent Jets by Stochastic Modelling Under Location Uncertanty Open
International audience
View article: Acknowledgments
Acknowledgments Open
who significantly boosted the love I have always had for mathematics since elementary school, and have facilitated, even if unconsciously, the projection of this love into an all-consuming passion for applying mathematics to solve engineer…
View article: The effect of flight on a turbulent jet: coherent structure eduction and resolvent analysis
The effect of flight on a turbulent jet: coherent structure eduction and resolvent analysis Open
We study coherent structures in subsonic turbulent jets subject to a flight stream. A thorough characterisation of the effects of a flight stream on the turbulent field was recently performed by Maia et al. ( Phys. Rev. Fluids , vol. 8, 20…
View article: Fast and robust method for screened Poisson lattice Green's function using asymptotic expansion and Fast Fourier Transform
Fast and robust method for screened Poisson lattice Green's function using asymptotic expansion and Fast Fourier Transform Open
We study the lattice Green's function (LGF) of the screened Poisson equation on a two-dimensional rectangular lattice. This LGF arises in numerical analysis, random walks, solid-state physics, and other fields. Its defining characteristic …
View article: Filtering dynamical systems using observations of statistics
Filtering dynamical systems using observations of statistics Open
We consider the problem of filtering dynamical systems, possibly stochastic, using observations of statistics. Thus, the computational task is to estimate a time-evolving density ρ(v,t) given noisy observations of the true density ρ†; this…
View article: Optimal frequency resolution for spectral proper orthogonal decomposition
Optimal frequency resolution for spectral proper orthogonal decomposition Open
We demonstrate that accurate computation of the spectral proper orthogonal decomposition (SPOD) critically depends on the choice of frequency resolution. Using both artificially generated data and large-eddy simulation data of a turbulent …
View article: An adaptive lattice Green's function method for external flows with two unbounded and one homogeneous directions
An adaptive lattice Green's function method for external flows with two unbounded and one homogeneous directions Open
We solve the incompressible Navier-Stokes equations using a lattice Green's function (LGF) approach, including immersed boundaries (IB) and adaptive mesh refinement (AMR), for external flows with one homogeneous direction (e.g. infinite cy…
View article: The effect of flight on a turbulent jet: coherent structure eduction and resolvent analysis
The effect of flight on a turbulent jet: coherent structure eduction and resolvent analysis Open
We study coherent structures in subsonic turbulent jets subject to a flight stream. A thorough characterisation of the effects of a flight stream on the turbulent field was recently performed by Maia et al. (2023) and fluctuation energy at…
View article: Filtering Dynamical Systems Using Observations of Statistics
Filtering Dynamical Systems Using Observations of Statistics Open
We consider the problem of filtering dynamical systems, possibly stochastic, using observations of statistics. Thus, the computational task is to estimate a time-evolving density $ρ(v, t)$ given noisy observations of the true density $ρ^\d…
View article: Two-point measurements on the acoustic field of subsonic turbulent jets
Two-point measurements on the acoustic field of subsonic turbulent jets Open
International audience
View article: Velocity gradient analysis of a head-on vortex ring collision
Velocity gradient analysis of a head-on vortex ring collision Open
We simulate the head-on collision between vortex rings with circulation Reynolds numbers of 4000 using an adaptive, multiresolution solver based on the lattice Green's function. The simulation fidelity is established with integral metrics …
View article: Method for portable, scalable, and performant GPU-accelerated simulation of multiphase compressible flow
Method for portable, scalable, and performant GPU-accelerated simulation of multiphase compressible flow Open
Multiphase compressible flows are often characterized by a broad range of space and time scales. Thus entailing large grids and small time steps, simulations of these flows on CPU-based clusters can thus take several wall-clock days. Offlo…
View article: Spectral proper orthogonal decomposition of harmonically forced turbulent flows
Spectral proper orthogonal decomposition of harmonically forced turbulent flows Open
Many turbulent flows exhibit time-periodic statistics. These include turbomachinery flows, flows with external harmonic forcing, and the wakes of bluff bodies. Many existing techniques for identifying turbulent coherent structures, however…
View article: Linear Analysis of Boundary-Layer Instabilities on a Finned-Cone at Mach 6
Linear Analysis of Boundary-Layer Instabilities on a Finned-Cone at Mach 6 Open
Boundary-layer instabilities for a finned cone at Mach=6, $Re=8.4 \times 10^6$ [m$^{-1}$], and zero incidence angle are examined using linear stability methods of varying fidelity and maturity, following earlier analysis presented in [doi.…
View article: Method for Scalable and Performant Gpu-Accelerated Simulation of Multiphase Compressible Flow
Method for Scalable and Performant Gpu-Accelerated Simulation of Multiphase Compressible Flow Open
View article: Global receptivity analysis: physically realizable input-output analysis
Global receptivity analysis: physically realizable input-output analysis Open
In the context of transition analysis, linear input-output analysis determines worst-case disturbances to a laminar base flow based on a generic right-hand-side volumetric/boundary forcing term. The worst-case forcing is not physically rea…
View article: Efficient global resolvent analysis via the one-way Navier–Stokes equations
Efficient global resolvent analysis via the one-way Navier–Stokes equations Open
Resolvent analysis is a powerful tool for modelling and analysing transitional and turbulent flows and, in particular, for approximating coherent flow structures. Despite recent algorithmic advances, computing resolvent modes for flows wit…
View article: Hybrid quadrature moment method for accurate and stable representation of non-Gaussian processes applied to bubble dynamics
Hybrid quadrature moment method for accurate and stable representation of non-Gaussian processes applied to bubble dynamics Open
Solving the population balance equation (PBE) for the dynamics of a dispersed phase coupled to a continuous fluid is expensive. Still, one can reduce the cost by representing the evolving particle density function in terms of its moments. …