The purpose of this work was to validate and apply a commercial computational fluid dynamics code with a hybrid RANS/LES turbulence computational model for a flow past a bluff body ultimately to help in the design of the caisson anchoring system during construction of a new adjacent span of the Tacoma Narrows Bridge.
The newly constructed Tacoma Narrows Bridge Piers represent large concrete floating caissons during their construction. For designing their mooring system the current force applied on the caissons in the Narrows must be known. The flow field around the caisson is highly complex and the calculation of the current load on the caisson by analytical means is difficult. On the other hand, model tests suffer from the distortion in the Reynolds number. Therefore, a two-prong approach was undertaken. Besides the fixed model test of the caissons for current forces, a CFD analysis of the flow around the caisson is chosen. A three-dimensional CFD approach is considered more appropriate than a two-dimensional one, since the bottom contour at the site is irregular and water depth is rather shallow. This paper discusses the CFD method and the results obtained from such analysis. The numerical analysis was carried out in both ebb and flood flow of the tidal current in the basin. One of the difficulties of the computational method is the very high Reynolds number encountered by the large current and large size of the caisson. The analysis is performed in both model and full scales so that the difference in the results may be investigated. Also, since the model test data are available, comparisons are made between the CFD and model test results on the drag and lift forces on the caisson.
The Columbia River in Washington State is threatened by the radioactive legacy of the cold war. Two hundred thousand cubic meters (fifty-three million US gallons) of radioactive waste is stored in 177 underground tanks (60% of the Nation’s radioactive waste). A vast complex of waste treatment facilities is being built to convert this waste into stable glass (vitrification). The waste in these underground tanks is a combination of sludge, slurry, and liquid. The waste will be transported to a pre-treatment facility where it will be processed before vitrification. It is necessary to keep the solids in suspension during processing. The mixing devices selected for this task are known as pulse-jet mixers (PJMs). PJMs cyclically empty and refill with the contents of the vessel to keep it mixed. The transient operation of the PJMs has been proven successful in a number of applications, but needs additional evaluation to be proven effective for the slurries and requirements at the Waste Treatment Plant (WTP). Computational fluid dynamic (CFD) models of mixing vessels have been developed to demonstrate the ability of the PJMs to meet mixing criteria. Experimental studies have been performed to validate these models. These tests show good agreement with the transient multiphase CFD models developed for this engineering challenge.
Transport and processing of nuclear waste for treatment and storage can involve unique and complex thermal and fluid dynamic conditions that pose potential for safety risk and/or design uncertainty and also are likely to be subjected to more precise performance requirements than in other industries. From an engineering analysis perspective, certainty of outcome is essential. Advanced robust methods for engineering analysis and simulation of critical processes can help reduce risk of design uncertainty and help mitigate or reduce the amount of expensive full-scale demonstration testing. This paper will discuss experience gained in applying computational fluid dynamics models to key processes for mixing, transporting, and thermal treatment of nuclear waste as part of designing a massive vitrification process plant that will convert high and low level nuclear waste into glass for permanent storage. Examples from industrial scale simulations will be presented. The computational models have shown promise in replicating several complex physical processes such as solid-liquid flows in suspension, blending of slurries, and cooling of materials at extremely high temperature. Knowledge gained from applying simulation has provided detailed insight into determining the most critical aspects of these complex processes that can ultimately be used to help guide the optimum design of waste handling equipment based on credible calculations while ensuring risk of design uncertainty is minimized.
A method to assess computational fluid dynamics (CFD) models for polydisperse granular solids in a multifluid flow is developed. The proposed method evaluates a consistency constraint, or a condition that an Eulerian multiphase solution for a monodisperse material in a single carrier fluid is invariant to an arbitrary decomposition into a pseudo-polydisperse mixture of multiple, identical fluid phases. The intent of this condition is to develop tests to assist model development and testing for multiphase fluid flows. When applied to two common momentum exchange models, the constraint highlights model failures for polydisperse solids interacting with a multifluid flow. It is found that when inconsistency occurs at the algebraic level, model failure clearly extends to application. When the models are reformulated to satisfy the consistency constraint, simple tests and application-scale simulations no longer display consistency failure.
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