Article
Mechanics
Ashwini Karmarkar, Jacqueline O'Connor
Summary: The study aims to analyze how increasing free-stream turbulence affects the flow response to longitudinal acoustic excitation. By studying the flow in the wake of a cylindrical bluff body under non-reacting and reacting conditions, we find that varying the level of free-stream turbulence can influence both the amplitude and symmetry of vortex shedding in the presence of longitudinal acoustic excitation.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
N. Swaminathan, N. Chakraborty
Summary: The dissipation rate of a scalar variance is related to the mean heat release rate in turbulent combustion. For non-premixed combustion, mixture fraction is the key scalar of interest, while a reaction progress variable is relevant for premixed combustion. The analysis shows a dependence on Karlovitz and Damkohler numbers in reactive scalar spectral density in premixed combustion.
Article
Thermodynamics
Fredrik Grovdal, Sigurd Sannan, Christoph Meraner, Tian Li, Terese Lovas
Summary: The study discusses a dimensional-decomposition approach for turbulent (reacting) flows by decomposing 3D into 3x1D. The research focuses on the Three-Dimensional Linear Eddy Model (LEM3D) and its recouplings, finding that the auxiliary coupling introduces large gradients leading to increased burning rates. Applications of LEM3D should be limited to areas where high-resolution treatment of scalar mixing and reaction is of particular interest.
FLOW TURBULENCE AND COMBUSTION
(2021)
Article
Thermodynamics
Ali Kord, Jesse Capecelatro
Summary: An adjoint-based framework is developed to measure exact sensitivity from high-fidelity simulations of turbulent reacting flows. It utilizes state-of-the-art numerical methods compatible with a discrete adjoint solver and employs a flamelet/progress variable approach for chemical reactions. The framework is demonstrated through gradient-based optimization on two configurations, showcasing its efficiency in manipulating large-scale space-time fields.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Mechanics
P. W. Agostinelli, B. Rochette, D. Laera, J. Dombard, B. Cuenot, L. Gicquel
Summary: The study proposes a static mesh refinement strategy based on flow physical quantities, detecting areas of interest for flow physics and recommending grid adaptation to enhance the accuracy of large eddy simulations. The strategy is detailed on two reacting-flow problems and shown to significantly improve predictions of flame stabilization.
Article
Computer Science, Interdisciplinary Applications
Ral Bielawski, Shivam Barwey, Supraj Prakash, Venkat Raman
Summary: Emerging supercomputing systems combine CPUs and GPUs to reach exascale capabilities with minimal energy footprint. This presents challenges for fluid solvers due to the differences in hardware architecture and operation between GPUs and CPUs. This work presents a general approach for efficient implementation of finite-volume based reacting flow solvers on heterogeneous systems. Specific algorithms are developed to handle compressible reacting flows, including chemical reactions, convection terms, and turbulence, ensuring GPU-based efficiency. The approach is demonstrated using the OpenFOAM software and shows excellent scalability on a large number of GPUs (> 3000) with constant throughput for a large number of control volumes.
COMPUTERS & FLUIDS
(2023)
Article
Mechanics
Francesco Pignatelli, Rixin Yu, Xue-Song Bai, Karl-Johan Nogenmyr
Summary: The study characterizes the propagation of premixed reacting waves using displacement speed S-d, which can be decomposed into three parts and has recently derived transport equations for better understanding. By analyzing four direct numerical simulation cases, it was found that surfaces propagating at large positive (negative) S-d tend to advance (retreat) faster, and the behavior is influenced by the density ratio between fresh and burned gases. Additionally, the distribution of curvature for the reaction-zone surface skews toward a negative value, i.e., the curvature center pointing to the burned product.
Article
Mechanics
Kaiwen Chen, Duo Xu, Baofang Song
Summary: In this study, we investigated the propagation of turbulent fronts in pipe flow at high Reynolds numbers by conducting direct numerical simulation. By using a combination of a moving frame of reference and an artificial damping technique, we were able to isolate the fronts in short periodic pipes and explore the bulk Reynolds number up to Re = 10(5). Our analysis revealed that the speed of the downstream front increases monotonically as the Reynolds number increases, whereas the speed of the upstream front agrees with previous studies. Based on our observations of the front dynamics, we proposed that both front speeds would continue to follow their respective monotonic trends as the Reynolds number increases further.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
S. F. Lewin, C. P. Caulfield
Summary: Motivated by the variation of local shear produced by internal waves in the ocean, this study investigates the effect of a time-dependent shear forcing on the evolution and mixing of turbulence produced by Kelvin-Helmholtz instability (KHI) through direct numerical simulations. The results demonstrate that turbulence produced by KHI with a decelerating shear mixes in a distinctly different way from the flow with constant background shear, with characteristics more in common with convectively driven flows.
JOURNAL OF FLUID MECHANICS
(2022)
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
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
Mechanics
J. G. Esler
Summary: It is well established that Lagrangian particle dispersion models for inhomogeneous turbulent flows must satisfy the 'well-mixed condition' in order to produce physically reasonable results. However, the well-mixed condition alone is not sufficient to uniquely define the dispersion model in more than one dimension, leading to the introduction of a spin condition to constrain the models. Models defined by the spin condition result in particles having the correct angular speed in turbulent flow.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Thermodynamics
Nikolaos Perakis, Oskar J. Haidn, Matthias Ihme
Summary: This study investigated a reacting boundary layer flow at elevated pressures, focusing on the effects of wall temperatures on chemical reactions. The results showed significant changes in reaction locations and heat loads caused by wall temperatures, as well as notable deviations in gas composition. Secondary reaction zones were identified, and their impact on heat release was discussed.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2021)
Review
Physics, Multidisciplinary
Amsini Sadiki, Senda Agrebi, Florian Ries
Summary: This paper provides a comprehensive review of the different contributions to entropy generation analysis (EGA) in turbulent combustion systems. It covers various parametric studies, experimental and numerical modeling works, and practical applications. The difficulties of performing comprehensive experiments and the lumped approach to calculating total entropy generation rate are discussed. Different modeling degrees of the entropy production terms are presented and exemplary investigations and validation cases are reported. The importance of EGA for optimizing combustion systems is highlighted and areas for future research are identified.
Article
Engineering, Marine
Taiji Tanaka, Yoshihiko Oishi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Chiharu Kawakita
Summary: The study demonstrated that air lubrication with repetitive bubble injection achieved superior efficiency in drag reduction compared to continuous bubble injection.
Article
Thermodynamics
Matthew Bonanni, Matthias Ihme
Summary: This study investigates the effects of preferential evaporation on the combustion behavior of multi-component spray flames. It is found that the preferential evaporation of more volatile components leads to changes in gas-phase composition and affects the combustion performance and reaction zones. Therefore, considering preferential evaporation behavior is necessary when constructing models for multi-component spray combustion.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Thermodynamics
Wai Tong Chung, Nguyen Ly, Matthias Ihme
Summary: This study assesses the utility of large eddy simulations (LES) for predicting HCCI combustion in a 3-D configuration. The simulation results show reasonable agreement with experimental data in terms of temperature fluctuations and ignition delay, and the predicted flame propagation modes also match the experimental observations. The findings demonstrate the practicality of FRC-LES for investigating multimode combustion regimes of HCCI combustion.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Energy & Fuels
Nguyen Ly, Arijit Majumdar, Matthias Ihme
Summary: The objective of this paper is to examine the fundamental mechanisms responsible for the transition between subcritical evaporation and supercritical dense-fluid-mixing in the absence of convection effects, specifically focusing on the liquid-vapor interfacial dynamics. The study characterizes the different physical behaviors exhibited by an n-dodecane nanoscale droplet placed in different nitrogen ambient conditions across the fuel's critical point and explores the underlying phase-exchange mechanisms. The findings show four regimes of evaporation/mixing behaviors and the distinction in the phase-exchange mechanisms in these four regimes are brought about by the different thermodynamic phases the droplet center can exhibit during the evaporation/mixing process.
Article
Thermodynamics
Jack Guo, Davy Brouzet, Wai Tong Chung, Matthias Ihme
Summary: Ducted fuel injection (DFI) is a proposed concept for reducing emissions by improving fuel-air mixing and reducing the formation of soot and other unwanted combustion products. This study uses large-eddy simulations to investigate the physical mechanisms and combustion processes of DFI, with a focus on the mixing process and the impact of fuel-ducting on combustion and pollutant emissions.
INTERNATIONAL JOURNAL OF ENGINE RESEARCH
(2023)
Article
Chemistry, Physical
Priyanka Muhunthan, Oscar Paredes Mellone, Thomas Kroll, Dimosthenis Sokaras, Matthias Ihme
Summary: This study combines X-ray Raman spectroscopy, molecular dynamics simulations, and density functional theory calculations to characterize the local electronic structure of supercritical CO2. It finds that X-ray Raman spectroscopy is a sensitive tool for studying the electronic properties of CO2 under challenging experimental conditions and provides unique insights into the electronic structure of supercritical fluids.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2023)
Article
Multidisciplinary Sciences
Filip Simeski, Matthias Ihme
Summary: Supercritical fluids, which have important implications in various scientific and engineering applications, exhibit complex network dynamics associated with localized molecular clusters. This structural and dynamical behavior can be accurately described by a hidden-variable network model, providing a basis to relate fluid microstructure to thermodynamic response functions.
NATURE COMMUNICATIONS
(2023)
Article
Physics, Fluids & Plasmas
Fangbo Li, Jack Guo, Bofeng Bai, Matthias Ihme
Summary: In this study, the authors analyze the turbulent energy transport in high-pressure transcritical flows and propose scaling laws for the turbulent length scales and turbulent kinetic energy budgets. The results show that the dissipation rate of turbulent kinetic energy is dominated by the enstrophy in the logarithmic layer and that the fluctuating viscosity attenuates the dissipation rate by reducing the shear strain and the enstrophy production. Real-fluid thermodynamic effects significantly change the turbulent heat flux and alter the density-fluctuation-related momentum-fluctuation statistics.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Thermodynamics
Guilherme C. Fraga, Bifen Wu, Matthias Ihme, Xinyu Zhao
Summary: This article presents an analytical approach for calculating radiative self-absorption in flames, aiming to provide an effective and computationally inexpensive tool for selecting radiation models in combustion applications. The one-dimensional non-local model approximates the flame structure as an infinitely long cylinder with properties varying only along the radial direction. The model is validated for different flame types and applied to study the radiation characteristics in high-pressure combustion, fire suppression, and hydrogen combustion.
COMBUSTION AND FLAME
(2023)
Article
Thermodynamics
Thorsten Zirwes, Guillaume Vignat, Edna R. Toro, Emeric Boigne, Khaled Younes, Dimosthenis Trimis, Matthias Ihme
Summary: Porous media combustion relies on internal heat recirculation to enhance flame speed. However, the accuracy of volume-averaged simulations is controversial. In this study, an open-source modeling framework is proposed to accurately simulate PMC using first-principles methods and X-ray computed microtomography. The framework shows significant improvements compared to empirical models.
COMBUSTION AND FLAME
(2023)
Article
Chemistry, Physical
Filip Simeski, Jiyue Wu, Sheng Hu, Theodore T. Tsotsis, Kristian Jessen, Matthias Ihme
Summary: This study investigates the impact of pore wall proximity, pore size, and temperature on the structure of nanoconfined ethane through experimental adsorption measurements and molecular dynamics simulations. The findings reveal an energetically favorable rearrangement of ethane molecules in the adsorption layer, which is significant for accurate estimation of gas-in-place and efficient design of gas separation membranes.
JOURNAL OF PHYSICAL CHEMISTRY C
(2023)
Article
Meteorology & Atmospheric Sciences
Sheide Chammas, Qing Wang, Tapio Schneider, Matthias Ihme, Yi-fan Chen, John Anderson
Summary: This study demonstrates the use of tensor processing units (TPUs) to simulate low clouds, providing valuable insights into their role in climate. The simulations conducted using TPUs show unprecedented speed and scalability, allowing for the generation of large datasets for training climate models.
JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS
(2023)
Article
Nanoscience & Nanotechnology
Philipp Rosenberger, Ritika Dagar, Wenbin Zhang, Arijit Majumdar, Marcel Neuhaus, Matthias Ihme, Boris Bergues, Matthias F. Kling
Summary: Droplets provide a unique platform for investigating laser-induced surface chemistry. This study demonstrates the application of reaction nanoscopy technique to propanediol nanodroplets and reveals the sensitivity of the technique to droplet size, charge, and surface chemistry. The results show enhanced production of methyl cations from 1,2-PDO droplets compared to 1,3-PDO droplets, highlighting the role of surface alignment in chemical reactions on droplets. These findings open up opportunities for spatio-temporal observations of charge dynamics and surface reactions on droplets.
Article
Thermodynamics
Emeric Boigne, Thorsten Zirwes, Dilworth Y. Parkinson, Guillaume Vignat, Priyanka Muhunthan, Harold S. Barnard, Alastair A. MacDowell, Matthias Ihme
Summary: Porous media combustion is a promising technology for efficient and clean combustion. However, the lack of understanding of interstitial combustion processes hinders its practical application and the development of predictive models. This study presents an integrated experimental and computational approach to examine porous media combustion, providing insights into the characteristics of the combustion process and suggesting potential improvements in modeling techniques.
COMBUSTION AND FLAME
(2024)
Article
Materials Science, Multidisciplinary
Laura Froute, Emeric Boigne, Isabelle C. Jolivet, Eric Chaput, Patrice Creux, Matthias Ihme, Anthony R. Kovscek
Summary: This study evaluates the capabilities of electron tomography (ET) for thin sections of shale, a complex nanoporous medium, and identifies the limited projection range and reconstruction as the main experimental bottlenecks.
MICROSCOPY AND MICROANALYSIS
(2023)
Article
Instruments & Instrumentation
Khaled Younes, Michael Poli, Priyanka Muhunthan, Ivan Rajkovic, Stefano Ermon, Thomas M. Weiss, Matthias Ihme
Summary: The advent of modern, ultrafast X-ray experiments has led to excessive data generation, which poses challenges for storage and hardware capabilities. This paper proposes using Bayesian optimization to tackle this problem, and demonstrates its versatility, robustness, and computational efficiency through experiments.
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT
(2023)