A Post-processing Algorithm for Cfd Dispersion Error Annihilation
A class of transient computational uid dynamics (CFD) solutions is especially prone to dispersion error yielding moderate to high distortion. Speciically, the universally intrinsic zero phase velocity for \22x" waves induces an error cascading to smaller wave number modes that appear as mesh scale solution oscillations. Artiicial viscosity and/or ux correction operators can diiuse this error mode, but may produce unacceptable amounts of dissipation in multidi-mensional embodiments. In this paper, a discrete solution reconstruction (RCN) procedure is developed and validated for monotonicity enhancement of dispersed (poor quality) 1-D, 2-D and 3-D solutions produced by nite diierence and nite element CFD algorithms. Reconstructed results for the veriication 1-D wave propagation, the benchmark 2-D rotating cone and the validation 3-D room species mass fraction contamination document that RCN can yield an absolutely dispersion-free reconstruction of any algorithm solution.
CFD experiment characterization of airborne contaminant transport for two practical 3-D room air flow fields
Abstract With the increasing concern for, and focus on, indoor air quality, determination of the distribution of airborne contaminants within rooms becomes of great interest. Computational fluid dynamics (CFD) techniques offer a means for simulation of contaminant transport processes, with quantitative richness of detail rarely possible in laboratory testing. Results of such “CFD experiments” are documented herein for two practical, low turbulence-level, thermal room air flow fields. The supply flow is tagged with a distinguishable species, and the resulting time-dependent concentration evolution throughout the room is predicted. The simulated full-scale room air flow field Reynolds numbers are 15,000 and 30,000, the Archimedes number ranges from 0.83 to 4.3, and simulation turbulent Schmidt number ranges an order of magnitude.
Numerical tools applied to power reactor noise analysis
In order to be able to calculate the space- and frequency-dependent neutron noise in real inhomogeneous systems in two-group theory, a code was developed for the calculation of the Green's function (dynamic transfer function) of such systems. This paper reports on the development as well as the test and application of the numerical tools employed. The code that was developed yields the space-dependence of the fluctuations of the neutron flux induced by fluctuating properties of the medium in the two-group diffusion approximation and in a two-dimensional representation of heterogeneous systems, for both critical systems and non-critical systems with an external source. Some applications of these tools to power reactor noise analysis are then described, including the unfolding of the parameters of the noise source from the induced neutron noise, measured at a few discrete locations throughout the core. Other concrete applications concern the study of the space-dependence of the Decay Ratio in Boiling Water Reactors, the noise-based estimation of the Moderator Temperature Coefficient of reactivity in Pressurized Water Reactors, the modeling of the beam- and shell-mode core-barrel vibrations in Pressurized Water Reactors, and the investigation of the validity of the point-kinetic approximation in subcritical systems driven by an external source. In most of these applications, calculations performed using the code are compared with at-power plant measurements. Power reactor noise analysis applications of the above type, i.e. core monitoring without disturbing plant operation, is of particular interest in the framework of the extensive program of power uprates worldwide.