arXiv subjects

Youhi Morii

Publications and source records attributed to Youhi Morii.

9 recordsLinked to original sources

arXiv2026

Quasi-DNS with chemical kinetics for near blow-out dynamics of a single multi-injection burner element for future gas turbine applications

Gas turbine combustors increasingly operate close to lean blow-out (LBO) limits, where small changes in fuel-air mixing or flow structure can destabilize the flame and alter near-blow-out dynamics. Conventional design practice relies mainly on Reynolds-averaged Navier-Stokes (RANS) simulations, which often overpredict turbulent mixing and cannot resolve unsteady flame anchoring and local extinction near burner hardware. We develop a Quasi-DNS workflow with detailed methane-air chemistry for a single element of a multiple-injection burner, modeled as a coaxial burner with a mixing tube and downstream combustion chamber, as a methodological basis for near-blow-out analysis. The workflow is implemented in OpenFOAM and comprises: (i) a simplified three-dimensional sector geometry with a 30-degree domain to capture circumferential vortices at the mixing tube outlet, (ii) boundary conditions and inlet profiles reproducing coaxial jet and preheated air conditions, (iii) a reduced Yang-Pope mechanism validated against GRI 3.0 using Cantera laminar flame speed, ignition delay, and counterflow diffusion flame calculations, (iv) grid generation and convergence checks based on flame structure and scalar dissipation rate, and (v) diagnostics including methane- and CO-based flame indices to classify local combustion modes. We demonstrate the workflow for a partially premixed methane flame at an overall equivalence ratio of phi = 0.45 and a perfectly premixed reference at the same phi. The Quasi-DNS results show limited mixing inside the mixing tube and strong vortical mixing at the outlet, leading to extended and structured heat-release regions that differ markedly from the smoother, more compact flames predicted by RANS. The methodology provides a reusable framework for analyzing flame structure, stabilization, and LBO-relevant dynamics in coaxial burners with mixing tubes.

physics.flu-dyn↗

arXiv2026

Duplicate-Aware Shift-and-Lift Carleman Linearization:Structure, Complexity, and Comparative Evaluation

The primary objective of this study is to remove duplicated monomial contributions that proliferate in Carleman linearization as state dimension and truncation order increase. To do so, we adopt a shift-and-lift architecture, since it exposes repeated exponent targets and allows duplicate-aware coefficient coalescing during lifted-operator assembly. This architecture also makes high-order truncation practical, but that regime intensifies local convergence and closure sensitivity for higher-order nonlinearities. We therefore pair shift-and-lift with a moving-center expansion so that shift and lift are updated jointly around evolving local centers, improving validity of the truncated model along the trajectory. The resulting workflow combines symmetry-reduced monomial bases, packed exponent-key indexing, and sparse triplet coalescing to preserve truncated affine dynamics while reducing index-resolution overhead and write-path irregularity. We analyze variable growth, preprocessing complexity, and truncation-induced error mechanisms, and we compare against Jacobian linearization through fixed-step error, admissible step size, and cost-at-target-accuracy criteria. Two benchmarks (bilinear driver and logistic interaction) show convergence under refinement for both approaches, with regime-dependent accuracy gains for the proposed method rather than universal superiority.

cs.CE↗

arXiv2026

Effects of Soret diffusion on the intrinsic instability of premixed hydrogen/air flames

Hydrogen flames exhibit multiple intrinsic instabilities. The low molar masses of H and H2 lead to significant Soret diffusion near the flame front; however, its influence on hydrogen flame instabilities remains to be quantified. This study investigates the effect of Soret diffusion on instability evolution dynamics via one-dimensional counterflow analysis and two-dimensional, high-fidelity direct numerical simulations covering both the linear growth regime and the fully developed nonlinear regime over a wide range of equivalence ratios (phi). In the linear regime, Soret diffusion increases the perturbation growth rate at phi < 1.7, especially under lean conditions, but reduces the growth rate at phi > 1.7. A similar sensitivity reversal is observed in the Markstein length near the peak equivalence ratio of unstretched laminar flame speed. In the nonlinear regime, Soret diffusion accelerates the formation of small-scale wrinkles in lean hydrogen flames and reduces the characteristic size of large-scale finger structure by one-third. An interesting observation is that, although Soret diffusion promotes preferential diffusion and increases the local flame displacement speed, the global fuel consumption rate decreases due to a reduction in the overall flame surface area. In addition, curvature-based flame segment analysis reveals a synergistic effect between Soret diffusion and Fickian diffusion that enhances/reduces the local equivalence ratio in positively/negatively curved regions of the flame front. The probability distributions of the Karlovitz number and the density-weighted displacement speed are also analyzed; results suggest that, for lean hydrogen flames, Soret diffusion broadens the distributions for both parameters, particularly on the positive side. These findings promise to advance the fundamental understanding of hydrogen flame dynamics under complex differential transport.

physics.flu-dyn↗

arXiv2025

GPU Benchmark through QPE Emulator with cuQuantum for Practical Quantum Applications

The quantum algorithm of Quantum Phase Estimation (QPE) was implemented to make the maximum use of GPU emulation with cuQuantum and CUDA Toolkit by NVIDIA. The input and output were handled by HDF5 to make the process as easy as possible. The computational time, VRAM usage, value error, and overhead was evaluated against the developed application. VRAM usage and the profiler analysis suggested that the developed application could make the maximum use of GPU capability.

quant-ph↗

arXiv2025

Weak Detonations Revisited: Uncovering Its General Nature Using Autoignitive Reaction Wave Concept

Weak detonations have remained experimentally elusive since their theoretical prediction, with previous realization attempts requiring either pathological detonations or Zeldovich spontaneous waves. Here, we demonstrate that stable weak detonations are naturally achieved through supersonic autoignitive reaction waves a recently proposed concept describing inherently stable reaction waves determined by inflow velocity conditions and autoignition characteristics. We establish the mathematical equivalence between autoignitive reaction waves and classical Rayleigh flow, proving that supersonic autoignitive reaction waves are indeed weak detonations. The underlying thermodynamic structure reveals Legendre conjugate variables linking normalized enthalpy and fuel consumption. Unlike previous approaches, our universal realization conditions require only that inlet velocity exceed the Chapman-Jouguet velocity and autoignition criteria be met applicable to any reactive system without specialized chemistry. This framework transforms weak detonations from theoretical curiosities to practically achievable phenomena, opening new possibilities for applications in supersonic combustion systems and astrophysical phenomena.

physics.flu-dyn↗

arXiv2023

General concept for autoignitive reaction wave covering from subsonic to supersonic regimes

We consider a one-dimensional (1D) autoignitive reaction wave in reactive flow system comprising unburned premixed gas entering from the inlet boundary and burned gas exiting from the outlet boundary. In such a 1D system at given initial temperature, it is generally accepted that steady-state solutions can only exist if the inlet velocity matches either the velocity of deflagration wave, as determined by the burning rate eigenvalue in the subsonic regime or the velocity of detonation wave as dictated by the Chapman-Jouguet (CJ) condition in the supersonic regime. In this study, we developed the general concept of "autoignitive reaction wave" and theoretically demonstrate that two distinct regimes that can maintain steady-state solutions both in subsonic and supersonic conditions. Based on this theory, we selected inlet velocities that are predicted to yield either steady-state or flashback solutions, and conducted numerical simulations. This novel approach revealed that steady-state solutions are possible not only at the velocity of the deflagration wave in the subsonic regime and the velocity of the detonation wave in the supersonic regime, but also across a broad range of inlet velocities. Furthermore, we identify a highly stable "autoignitive reaction wave" that emerges when the inlet velocity surpasses the velocity of detonation wave, devoid of the typical shock wave commonly seen in detonation waves. This "supersonic autoignitive reaction wave" lacks the instability-inducing detonation cell structure, suggesting the potential for the development of novel combustor concepts.

physics.flu-dyn↗

arXiv2023

What connects ignition and deflagration? -- On explosive transition of deflagration

The general relation between ignition and deflagration analyses was studied theoretically and computationally. Simple analysis showed that the temporal evolutions of normalized fuel mass fraction and the normalized temperature in a 0D homogeneous ignition are equivalent to the spatial evolutions of those in a 1D laminar premixed flame at Lewis number of unity if a spatio-temporal transformation of the flame is applied. Furthermore, computations showed that the degree of reduction in normalized fuel mass fraction in the preheat zone was found to be in the following order: when the Lewis number is less than unity, when the Lewis number is unity (= ignition), and when the Lewis number is greater than unity. This suggested that ignition in the preheat zone near the explosive transition can only occur for 1D laminar premixed flames with Lewis number greater than unity. In summary, the characteristic times of ignition and flame propagation can be of the same order of magnitude in premixed gases compressed by piston in engines or shock waves, and thus the Lewis number determines the existence of premixed flame structure under such conditions.

physics.flu-dyn↗

arXiv2022

Carleman linearization approach for chemical kinetics integration toward quantum computation

The Harrow, Hassidim, Lloyd (HHL) algorithm is a quantum algorithm expected to accelerate solving large-scale linear ordinary differential equations (ODEs). To apply the HHL to non-linear problems such as chemical reactions, the system must be linearized. In this study, Carleman linearization was utilized to transform nonlinear first-order ODEs of chemical reactions into linear ODEs. Although this linearization theoretically requires the generation of an infinite matrix, the original nonlinear equations can be reconstructed. For the practical use, the linearized system should be truncated with finite size and analysis precision can be determined by the extent of the truncation. Matrix should be sufficiently large so that the precision is satisfied because quantum computers can treat. Our method was applied to a one-variable nonlinear dy/dt = -y^2 system to investigate the effect of truncation orders in Carleman linearization and time step size on the absolute error. Subsequently, two zero-dimensional homogeneous ignition problems for H2/air and CH4/air gas mixtures were solved. The results revealed that the proposed method could accurately reproduce reference data. Furthermore, an increase in the truncation order in Carleman linearization improved accuracy even with a large time-step size. Thus, our approach can provide accurate numerical simulations rapidly for complex combustion systems.

math.NA↗

arXiv2019

Optimization of One-parameter Family of Integration Formulae for Solving Stiff Chemical-kinetic ODEs

A fast and robust Jacobian-free time-integration method - called Minimum-error Adaptation of a Chemical-Kinetic ODE Solver (MACKS) - for solving stiff ODEs pertaining to chemical-kinetics is proposed herein. The MACKS formulation is based on optimization of the one-parameter family of integration formulae coupled with a dual time-stepping method to facilitate error minimization. The proposed method demonstrates higher accuracy compared to the method - Extended Robustness-enhanced numerical algorithm (ERENA) - previously proposed by the authors. Additionally, when this method is employed in homogeneous-ignition simulations, it facilitates realization of faster performance compared to the Variable-coefficient ODE solver (VODE).

physics.flu-dyn↗