80 research outputs found
Development of a moment method to solve the three-dimensional boundary layer equations
Moment method for solving nonsimilar laminar boundary layer equations for three dimensional cross flo
On the calculation of three dimensional laminar boundary layer flows
An approximation which reduces the computation of three dimensional, laminar, compressible, boundary layer equations to the problem of solving two dimensional type boundary layer equations is presented. A comparison of this method with a fully three dimensional boundary layer calculation is provided
Finite difference solution to the three-dimensional, incompressible thermal energy boundary-layer equation
An implicit numerical method has been adopted for the solution to the three-dimensional, energy boundary-layer equation. The energy equation is written in terms of a dimensionless temperature function, the relative stagnation-enthalpy difference, and transformed by the introduction of a Blasius-type transformation of coordinates as well as dimensionless stream functions. The method is applied to the problem consisting of an infinite cylinder joined with its axis perpendicular to a thin, flat, heated plate. A Prandtl number equal to one is simply considered
A fast, low-memory, and stable algorithm for implementing multicomponent transport in direct numerical simulations
Implementing multicomponent diffusion models in reacting-flow simulations is
computationally expensive due to the challenges involved in calculating
diffusion coefficients. Instead, mixture-averaged diffusion treatments are
typically used to avoid these costs. However, to our knowledge, the accuracy
and appropriateness of the mixture-averaged diffusion models has not been
verified for three-dimensional turbulent premixed flames. In this study we
propose a fast,efficient, low-memory algorithm and use that to evaluate the
role of multicomponent mass diffusion in reacting-flow simulations. Direct
numerical simulation of these flames is performed by implementing the
Stefan-Maxwell equations in NGA. A semi-implicit algorithm decreases the
computational expense of inverting the full multicomponent ordinary diffusion
array while maintaining accuracy and fidelity. We first verify the method by
performing one-dimensional simulations of premixed hydrogen flames and compare
with matching cases in Cantera. We demonstrate the algorithm to be stable, and
its performance scales approximately with the number of species squared. Then,
as an initial study of multicomponent diffusion, we simulate premixed,
three-dimensional turbulent hydrogen flames, neglecting secondary Soret and
Dufour effects. Simulation conditions are carefully selected to match
previously published results and ensure valid comparison. Our results show that
using the mixture-averaged diffusion assumption leads to a 15% under-prediction
of the normalized turbulent flame speed for a premixed hydrogen-air flame. This
difference in the turbulent flame speed motivates further study into using the
mixture-averaged diffusion assumption for DNS of moderate-to-high Karlovitz
number flames.Comment: 36 pages, 14 figure
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Assessing Mass Diffusion Modeling in Premixed Flames
Implementing multicomponent diffusion in numerical combustion studies is computationally expensive due to the challenges involved in computing diffusion coefficients. As a result, mixture-averaged diffusion treatments or simpler methods are used to avoid these costs. However, the accuracy and appropriateness of the mixture-averaged diffusion model has not been verified for three-dimensional turbulent premixed flames. This study evaluates the role of multicomponent mass diffusion for a range of premixed, laminar and turbulent hydrogen, n-heptane, and toluene flames, representing a range of fuel Lewis numbers. Secondary Soret and Dufour effects are neglected to isolate the impact of mass diffusion from thermal diffusion effects. Direct numerical simulation (DNS) of these flames is performed by implementing the Stefan--Maxwell equations in the DNS code NGA. A low-memory, semi-implicit algorithm decreases the computational expense of inverting the full multicomponent ordinary diffusion array while maintaining simulation accuracy and stability. The algorithm is demonstrated to be stable, and verified against one-dimensional premixed hydrogen flames in Cantera. A priori analysis shows significant errors in the diffusion flux vectors for mixture-averaged diffusion in regions of high flame curvature. These errors seem to distort local transport, impacting viscous dissipation and altering global flame statistics such as the normalized turbulent flame speed by modifying the average internal flame structure. In general, these results demonstrate that mixture-averaged diffusion may not fully capture the complexity of full multicomponent diffusion
A Nonsteady Heat Conduction Code with Radiation Boundary Conditions* H
Abstract A heat-transfer model for studying the temperature build-up in graphite blankets for fusion reactors is presented. In essence, the computer code developed is for two-dimensional, nonsteady heat conduction in heterogeneous, anisotropic solids with nonuniform internal heating. Thermal radiation as well as bremsstrahlung radiation boundary conditions are included, numerical calculations are performed for two design options by varying the wall loading, bremsstrahlung, surface layer thickness and thermal conductivity, blanket dimensions, time step and grid size. Mfl\ 1 I introductio
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Nonsteady heat conduction code with radiation boundary conditions
A heat-transfer model for studying the temperature build-up in graphite blankets for fusion reactors is presented. In essence, the computer code developed is for two-dimensional, nonsteady heat conduction in heterogeneous, anisotropic solids with nonuniform internal heating. Thermal radiation as well as bremsstrahlung radiation boundary conditions are included. Numerical calculations are performed for two design options by varying the wall loading, bremsstrahlung, surface layer thickness and thermal conductivity, blanket dimensions, time step and grid size. (auth
The M-Machine Multicomputer
The M-Machine is an experimental multicomputer being developed to test architectural concepts motivated by the constraints of modern semiconductor technology and the demands of programming systems. The M- Machine computing nodes are connected with a 3-D mesh network; each node is a multithreaded processor incorporating 12 function units, on-chip cache, and local memory. The multiple function units are used to exploit both instruction-level and thread-level parallelism. A user accessible message passing system yields fast communication and synchronization between nodes. Rapid access to remote memory is provided transparently to the user with a combination of hardware and software mechanisms. This paper presents the architecture of the M-Machine and describes how its mechanisms maximize both single thread performance and overall system throughput
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