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.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.