1,721,232 research outputs found
HTR-1.2 solver: Hypersonic Task-based Research solver version 1.2
No full textWe present an updated version of the open-source Hypersonics Task-based Research (HTR) solver for hypersonic aerothermodynamics. The solver, whose first version was presented in Di Renzo et al. (2020), is designed for direct numerical simulation (DNS) of canonical hypersonic flows at high Reynolds numbers in which thermo-chemical effects induced by high temperatures are relevant. The solver relies on high-order spatial discretization on structured meshes and efficient time integrators for stiff systems within the Regent/Legion software stack, which makes the code highly portable and scalable in CPU and GPU-based supercomputers. The new version herein presented includes several optimizations and new tools for data analysis, along with novel user option for hybrid skew-symmetric/targeted essentially non-oscillatory numerics, to offer higher computational efficiency and lower numerical dissipation at moderate Mach numbers, inclusion of a new combustion mechanism for methane and oxygen, and new recycling–rescaling inlet boundary conditions targeted to the simulation of fully developed turbulent boundary layers. New version program summary: Program Title: Hypersonics Task-based Research solver CPC Library link to program files: http://dx.doi.org/10.17632/9zsxjtzfr7.2 Developer's repository link: https://github.com/stanfordhpccenter/HTR-solver.git Licensing provisions: BSD 2-clause Programming language: Regent, C++, and CUDA Journal Reference of previous version: Di Renzo, M., Fu, L., & Urzay, J. (2020). HTR solver: An open-source exascale-oriented task-based multi-GPU high-order code for hypersonic aerothermodynamics. Computer Physics Communications, 107262. Does the new version supersede the previous version?: Yes Reasons for the new version: Release of new features Summary of revisions: • New optional sixth-order hybrid scheme has been implemented (activated by the flag “hybridScheme” in the input file). The scheme combines the energy-preserving properties of a sixth-order skew-symmetric central difference scheme [1] in smooth flow regions with the shock-capturing properties of a sixth-order targeted essentially non-oscillatory (TENO) scheme at points where shocks are involved. The switch between the two schemes is controlled by a TENO sensor whose cutoff value is adapted based on the maximum value of a modified Ducros sensor [2] across the reconstruction stencil. If the flag “hybridScheme” is set to false, the numerical scheme will revert to the TENO6-A scheme released in the previous version of the solver [3]; • New recycling–rescaling inflow boundary conditions [4,5] for the simulation of turbulent compressible boundary layers are now available to the user; • Support for Legion tracing, which significantly improves the strong scalability of the solver, has been implemented; • A diagnostic tool to monitor the time evolution of the flow variables in a subvolume of the computational domain is now available; • A single-step chemistry mechanism for methane/oxygen combustion has been added to the mixtures handled by the HTR solver; • Sample scripts for strong scaling have been added to the “testcases” directory; • Unit test and regression test suites have been added to the repository; • The input file scheme has been modified in order to reduce verbosity and increase flexibility in specifying the boundary conditions and type of gas mixture; • Hyperbolic sine stretching functions have been made available to users during the grid generation process; • Computationally intensive tasks have been ported to C++ and CUDA in order to achieve higher efficiency on all hardware; • Several optimizations of the tasks body and mapper have been implemented in order to increase the computational efficiency and reduce the memory footprint. Nature of problem: This code solves the Navier–Stokes equations at hypersonic Mach numbers including finite-rate chemistry for dissociating air and multicomponent transport. The solver is designed for direct numerical simulations (DNS) of transitional and turbulent hypersonic turbulent flows under high-enthalpy conditions, and it accounts for thermochemical effects (vibrational excitation and chemical dissociation). Solution method: This code uses a low-dissipation sixth-order schemes for the spatial discretization of the conservation equations on Cartesian stretched meshes. Time advancement is carried out by either an explicit method if chemistry is slow, hence not introducing additional stiffness, or by an operator-splitting algorithm whereby chemical production rates are handled implicitly. Additional comments including restrictions and unusual features: The HTR solver builds on the runtime Legion [6,7] and is written in the programming language Regent [8,9] developed at Stanford University. Instructions for installation of the components are provided in the README file enclosed with the HTR solver and in the Legion repository [6]. References [1] S. Pirozzoli, Journal of Computational Physics 229 (2010) 7180–7190. https://doi.org/10.1016/j.jcp.2010.06.006. F. Ducros, F. Laporte, T. Soulères, V. Guinot, P. Moinat, B. Caruelle, Journal of Computational Physics 161 (2000) 114–139. https://doi.org/10.1006/jcph.2000.6492. M. Di Renzo, L. Fu, J. Urzay, Computer Physics Communications 255 (2020) 107262. https://doi.org/10.1016/j.cpc.2020.107262. T. S. Lund, X. Wu, K. D. Squires, Journal of Computational Physics 140 (1996) 233–258. https://doi.org/10.1006/jcph.1998.5882. S. Pirozzoli, M. Bernardini, F. Grasso, Journal of Fluid Mechanics 657 (2010) 361–393. https://doi.org/10.1017/S0022112010001710. Legion web page, 2020. URL:https://legion.stanford.edu. M. Bauer, S. Treichler, E. Slaughter, A. Aiken, Legion: Expressing locality and independence with logical regions, International Conference for High Performance Computing, Networking, Storage and Analysis, SC (2012), IEEE. Regent web page, 2020. URL:http://regent-lang.org. E. Slaughter, W. Lee, S. Treichler, M. Bauer, A. Aiken, SC ’15: Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis (2015) 1–12,. https://doi.org/10.1145/2807591.2807629
Sostenere la relazione genitore-figlio nell'autismo. L'interpretazione tramite il triangolo di Losanna
No full textDirect numerical simulation of a hypersonic transitional boundary layer at suborbital enthalpies
No full textA Mach-10 hypersonic boundary layer of air overriding a cold, isothermal, non-catalytic flat wall, and with a stagnation enthalpy of 21.6 MJ kg(-1), is analysed using direct numerical simulations. The calculations include multicomponent transport, equilibrium vibrational excitation and chemical kinetics for air dissociation. The initially laminar boundary layer undergoes transition to turbulence by the resonance of a two-dimensional mode injected by a suction-and-blowing boundary condition imposed over a narrow spanwise porous strip. The ensuing turbulent boundary layer has a momentum Reynolds number of 3826 near the outflow of the computational domain. The relatively low temperature of the free stream renders the air chemically frozen there. However, the high temperatures generated within the boundary layer by viscous aerodynamic heating, peaking at a wall-normal distance y(star) similar or equal to 10-20 in semi-local viscous units, lead to air dissociation in under-equilibrium amounts equivalent to 4 %-7% on a molar basis of atomic oxygen, along with smaller concentrations of nitric oxide, which is mainly produced by the Zel'dovich mechanism, and of atomic nitrogen, the latter being mostly in steady state. A statistical analysis of the results is provided, including the streamwise evolution of (a) the skin friction coefficient and dimensionless wall heat flux; (b) the mean profiles of temperature, velocity, density, molar fractions, chemical production rates and chemical heat-release rate; (c) the Reynolds stresses and root-mean-squares of the fluctuations of temperature, density, pressure, molar fractions and chemical heat-release rate; and (d) the temperature/velocity and mass-fraction/velocity correlations
Publisher Correction: Aerodynamic generation of electric fields in turbulence laden with charged inertial particles (Nature Communications (2018) DOI: 10.1038/s41467-018-03958-7)
No full textThe original version of this Article contained an error in the last sentence of the second paragraph of the 'Atmospheric rarefaction effects' section of the Results, which incorrectly read 'The other one emulates the rarefied, CO2-rich Martian atmosphere (μ b = 1.3 × 10-5 N s m-2) at 6.9 mbar and 210 K, which gives ρ b = 1.6 × 10-12 kg m-3.' The correct version states ρ b = 1.6 × 10-2 kg m-3' in place of ρ b = 1.6 × 10-12 kg m-3'. This has been corrected in both the PDF and HTML versions of the Article
Direct numerical simulation of a hypersonic transitional boundary layer at suborbital enthalpies
Full text linkA Mach-10 hypersonic boundary layer of air overriding a cold, isothermal, non-catalytic flat wall, and with a stagnation enthalpy of 21.6 MJ kg−1, is analysed using direct numerical simulations. The calculations include multicomponent transport, equilibrium vibrational excitation and chemical kinetics for air dissociation. The initially laminar boundary layer undergoes transition to turbulence by the resonance of a two-dimensional mode injected by a suction-and-blowing boundary condition imposed over a narrow spanwise porous strip. The ensuing turbulent boundary layer has a momentum Reynolds number of 3826 near the outflow of the computational domain. The relatively low temperature of the free stream renders the air chemically frozen there. However, the high temperatures generated within the boundary layer by viscous aerodynamic heating, peaking at a wall-normal distance y⋆≃10--20 in semi-local viscous units, lead to air dissociation in under-equilibrium amounts equivalent to 4 %–7 % on a molar basis of atomic oxygen, along with smaller concentrations of nitric oxide, which is mainly produced by the Zel'dovich mechanism, and of atomic nitrogen, the latter being mostly in steady state. A statistical analysis of the results is provided, including the streamwise evolution of (a) the skin friction coefficient and dimensionless wall heat flux; (b) the mean profiles of temperature, velocity, density, molar fractions, chemical production rates and chemical heat-release rate; (c) the Reynolds stresses and root-mean-squares of the fluctuations of temperature, density, pressure, molar fractions and chemical heat-release rate; and (d) the temperature/velocity and mass-fraction/velocity correlations
Aerodynamic generation of electric fields in turbulence laden with charged inertial particles
No full textSelf-induced electricity, including lightning, is often observed in dusty atmospheres. However, the physical mechanisms leading to this phenomenon remain elusive as they are remarkably challenging to determine due to the high complexity of the multi-phase turbulent flows involved. Using a fast multi-pole method in direct numerical simulations of homogeneous turbulence laden with hundreds of millions of inertial particles, here we show that mesoscopic electric fields can be aerodynamically created in bi-disperse suspensions of oppositely charged particles. The generation mechanism is self-regulating and relies on turbulence preferentially concentrating particles of one sign in clouds while dispersing the others more uniformly. The resulting electric field varies over much larger length scales than both the mean inter-particle spacing and the size of the smallest eddies. Scaling analyses suggest that low ambient pressures, such as those prevailing in the atmosphere of Mars, increase the dynamical relevance of this aerodynamic mechanism for electrical breakdown
A mixture fraction space model for counterflow diffusion flames with incident electric field
No full textApplying an external electric field is a well-known strategy to control combustion processes. However, the high computational complexity of the numerical approaches formulated so far often forestalls the study of configurations of practical and scientific interest. This work proposes a reduced order model for predicting the behaviour of diffusion flames impinged by an external electric field that is based on the classic mixture fraction space formulation. The model takes into account differential diffusion effects as wells as the electric drift of ions in order to predict the species distribution in the mixing layer. The results obtained with the proposed model are in good agreement with those of the two-dimensional calculations presented by Di Renzo et al. (2018) for the case of a methane/air laminar counterflow diffusion flames impinged by sub-breakdown DC electric fields. The reduction of the computational cost associated with the prediction of each flame by a factor one million has allowed the authors to perform a preliminary exploration of the diffusion flame phase-space, in particular defining the variation of the ion-current produced by the reacting layer along its S-curve
HTR-1.3 solver: Predicting electrified combustion using the hypersonic task-based research solver
No full textThis manuscript presents an updated open-source version of the Hypersonics Task-based Research (HTR) solver. The solver, whose main features are presented in Di Renzo et al. (2020) [9] and Di Renzo & Pirozzoli (2021) [10], is designed for direct numerical simulation of reacting flows at high Reynolds numbers. This new version extends the applications of the HTR solver to turbulent combustion in the presence of external electric fields. In particular, a new distributed Poisson solver compatible with heterogeneous architectures has been incorporated in the algorithm to compute the electric potential distribution in bi-periodic configurations. The drift fluxes of the electrically charged species are now included in the transport equations using a targeted essentially non-oscillatory scheme. A verification of these new features of the solver is provided using one-dimensional burner stabilized flames, whereas a three dimensional turbulent flame is utilized to discuss the scalability of the proposed numerical tool. (C) 2021 Elsevier B.V. All rights reserved
LoS MIMO-Arrays vs. LoS MIMO-Surfaces
No full textThe wireless research community has expressed major interest in the sub-terahertz band for enabling mobile communications in future wireless networks. The sub-terahertz band offers a large amount of available bandwidth and, therefore, the promise to realize wireless communications at optical speeds. At such high frequency bands, the transceivers need to have larger apertures and need to be deployed more densely than at lower frequency bands. These factors proportionally increase the far-field limit and the spherical curvature of the electromagnetic waves cannot be ignored anymore. This offers the opportunity to realize spatial multiplexing even in line-of-sight channels. In this paper, we overview and compare existing design options to realize spatial multiplexing in line-of-sight multi-antenna channel
Bit Error Rate and Outage Analysis for Differential UWB Receivers in Log-Normal Fading Channels
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