1,720,992 research outputs found
Block-structured Adaptive Mesh Refinement - Theory, Implementation and Application
No full textStructured adaptive mesh refinement (SAMR) techniques can enable cutting-edge simulations of problems governed by conservation laws. Focusing on the strictly hyperbolic case, these notes explain all algorithmic and mathematical details of a technically relevant implementation tailored for distributed memory computers. An overview of the background of commonly used finite volume discretizations for gas dynamics is included and typical benchmarks to quantify accuracy and performance of the dynamically adaptive code are discussed. Large-scale simulations of shock-induced realistic combustion in non-Cartesian geometry and shock-driven fluid-structure interaction with fully coupled dynamic boundary motion demonstrate the applicability of the discussed techniques for complex scenarios
Scalable adaptive lattice Boltzmann–LES Solver for high Reynolds number flows in porous media
No full textThe present study employs the adaptive lattice Boltzmann solver AMROC-LBM to numerically investigate turbulent flow through a wind tunnel containing porous media with a blockage ratio of 0.5. The porous structure comprises two interlaced cubic arrays, designed to emulate a configuration under concurrent experimental investigation. To resolve turbulence characteristics, a large eddy simulation (LES) framework is integrated into the lattice Boltzmann method (LBM), enabling accurate capture of large-scale flow structures while modelling subgrid-scale effects. Our in-house solver has been rigorously validated against established experimental and numerical benchmarks, with the results demonstrating close agreement, thereby confirming the reliability of the computational methodology. A scalability analysis confirms the solver’s computational efficiency on parallel architectures
Large-eddy simulation of Richtmyer-Meshkov instability in a converging geometry
Full text linkThe Richtmyer-Meshkov instability (RMI) refers to the baroclinic generation of vorticity at a perturbed density interface when impacted by a shock wave. It is often thought of as the impulsive limit of the Rayleigh-Taylor instability (RTI). The fluid dynamics video "large-eddy simulations (LES) of RMI in a converging geometry" shows the mixing of materials resulting from the interaction of an imploding cylindrical shock wave with a concentric perturbed interface that separates outside light gas from heavy gas (initially 5 times denser) inside a wedge. At the initial impact, the incident shock Mach number is either 1.3 or 2.0. The present canonical simulations support recent interests on compressible turbulent mixing in converging geometries relevant to both inertial confinement fusion and core-collapse supernovae dynamics.Subcontract no. B341492 of DoE contract W-7405-ENG-4
An adaptive high-order hybrid scheme for compressive, viscous flows with detailed chemistry
No full textA hybrid weighted essentially non-oscillatory (WENO)/centered-difference numerical method, with low numerical dissipation, high-order shock-capturing, and structured adaptive mesh refinement (SAMR), has been developed for the direct numerical simulation of the multicomponent, compressible, reactive Navier–Stokes equations. The method enables accurate resolution of diffusive processes within reaction zones. The approach combines time-split reactive source terms with a high-order, shock-capturing scheme specifically designed for diffusive flows. A description of the order-optimized, symmetric, finite difference, flux-based, hybrid WENO/centered-difference scheme is given, along with its implementation in a high-order SAMR framework. The implementation of new techniques for discontinuity flagging, scheme-switching, and high-order prolongation and restriction is described. In particular, the refined methodology does not require upwinded WENO at grid refinement interfaces for stability, allowing high-order prolongation and thereby eliminating a significant source of numerical diffusion within the overall code performance. A series of one-and two-dimensional test problems is used to verify the implementation, specifically the high-order accuracy of the diffusion terms. One-dimensional benchmarks include a viscous shock wave and a laminar flame. In two-space dimensions, a Lamb–Oseen vortex and an unstable diffusive detonation are considered, for which quantitative convergence is demonstrated. Further, a two-dimensional high-resolution simulation of a reactive Mach reflection phenomenon with diffusive multi-species mixing is presented
Parametric study of detonation initiation using a hot jet in supersonic combustible mixtures
No full textThe effects of various flow or geometry parameters on detonation initiation in supersonic combustible mixtures using a hot jet were investigated, including the free stream Mach number Ma?, the hot jet Mach number Maj, the free stream pressure P?, the hot jet pressure Pj, the diameter of the hot jet Dj, and the height of the free stream channel Hc. The results show that there exists a free stream Mach number range (Ma?min, Ma?max) for the successful initiation. When Ma? is beyond that range, the hot jet is not able to initiate the detonation and the flow field maintains a stable shock wave or shock reflection induced by the hot jet. For the other parameters, including the hot jet Mach number, the free stream pressure, the hot jet pressure, the diameter of the hot jet, and the height of the free stream channel Hc, there exists a critical value for the detonation initiation. For the hot jet Mach number Maj, the hot jet pressure Pj, the diameter of the hot jet Dj, when they are larger than the critical values, the initiation can be realized eventually and the larger the parameters the faster the initiation. Otherwise, the flow field will maintain the final stable state as the shock wave or shock reflection. For the free stream pressure P? and the height of the free stream channel Hc, when they are larger than the critical values, the flow field will also maintain the final stable state. Otherwise, the detonation initiation can be realized eventually and the smaller the parameters the faster the initiation
A reliable split-step Fourier method for the propagation equation of ultra-fast pulses in single-mode optical fibers
No full textThe extension to the split-step Fourier method (SSFM) for Schro?dinger-type pulse propagation equations that we propose in this article is designed with the accurate simulation of pulses in the femtosecond regime in single-mode communication fibers in mind. We show that via an appropriate operator splitting scheme, Kerr nonlinearity and the self-steepening and stimulated Raman scattering terms can be combined into a single sub-step consisting of an inhomogeneous quasilinear first-order hyperbolic system for the real-valued quantities intensity and phase. First- and second-order accurate shock-capturing upwind schemes have been developed specifically for this nonlinear sub-step, which enables the accurate and oscillation-free simulation of signals under the influence of Raman scattering and extreme self-steepening with the SSFM. Benchmark computations of ultra-fast Gaussian pulses in fibers with strong nonlinearity demonstrate the superior approximation properties of the proposed approach
Hydrodynamic instabilities in gaseous detonations: comparison of Euler, Navier–Stokes, and large-eddy simulation
Full text linkA large-eddy simulation is conducted to investigate the transient structure of an unstable detonation wave in two dimensions and the evolution of intrinsic hydrodynamic instabilities. The dependency of the detonation structure on the grid resolution is investigated, and the structures obtained by large-eddy simulation are compared with the predictions from solving the Euler and Navier–Stokes equations directly. The results indicate that to predict irregular detonation structures in agreement with experimental observations the vorticity generation and dissipation in small scale structures should be taken into account. Thus, large-eddy simulation with high grid resolution is required. In a low grid resolution scenario, in which numerical diffusion dominates, the structures obtained by solving the Euler or Navier–Stokes equations and large-eddy simulation are qualitatively similar. When high grid resolution is employed, the detonation structures obtained by solving the Euler or Navier–Stokes equations directly are roughly similar yet equally in disagreement with the experimental results. For high grid resolution, only the large-eddy simulation predicts detonation substructures correctly, a fact that is attributed to the increased dissipation provided by the subgrid scale model. Specific to the investigated configuration, major differences are observed in the occurrence of unreacted gas pockets in the high-resolution Euler and Navier–Stokes computations, which appear to be fully combusted when large-eddy simulation is employed
Effects of hot jet on detonation initiation and propagation in supersonic combustible mixtures
No full textThe effects of a hot jet on detonation initiation and propagation in supersonic combustible mixtures has been studied with two-dimensional numerical simulations with the open-source program AMROC that uses a block-structured adaptive mesh refinement method. Results indicate that the hot jet could ignite the detonation effectively in supersonic combustible mixtures like a pneumatic ramp. After the realization of the detonation initiation, the hot jet can still play an important role on the detonation propagation during its continuous ejection. For a hot jet with certain diameter, it can result in an overdriven detonation with almost constant overdrive degree. After the shutdown of the hot jet, the stable CJ detonation combustion was realized finally in the supersonic combustible mixtures. With the re-ejection of the hot jet, the failed detonation could be reinitiated quickly. Through the control of the re-ejection of the hot jet, it plays a key role not only in the initiation process, but also in the subsequent continuous detonation combustion period
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
