Graduate Thesis Or Dissertation
 

Stability improvement of the one-dimensional two-fluid model for horizontal two-phase flow with model unification

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qz20sw77t

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  • The next generation of nuclear safety analysis computer codes will require detailed modeling of two-phase fluid flow. The most complete and fundamental model used for these calculations is known as the two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links the two phases together with six conservation equations. A major drawback is that the current two-fluid model, when area-averaged to create a one-dimensional model, becomes ill-posed as an initial value problem when the gas and liquid velocities are not equal. The importance of this research lies in obtaining a model that overcomes this difficulty. It is desired to develop a modified one-dimensional two-fluid model for horizontal flow that accounts for the pressure difference between the two phases, due to hydrostatic head, with the implementation of a void fraction distribution parameter. With proper improvement of the one-dimensional two-fluid model, the next generation of nuclear safety analysis computer codes will be able to predict, with greater precision, the key safety parameters of an accident scenario. As part of this research, an improved version of the one-dimensional two-fluid model for horizontal flows was developed. The model was developed from a theoretical point of view with the three original distribution parameters simplified down to a single parameter. The model was found to greatly enhance the numerical stability (hyperbolicity) of the solution method. With proper modeling of the phase distribution parameter, a wide range of flow regimes can be modeled. This parameter could also be used in the future to eliminate the more subjective flow regime maps that are currently implemented in today's multiphase computer codes. By incorporating the distribution parameter and eliminating the flow regime maps, a hyperbolic model is formed with smooth transitions between various flow regimes, eliminating the unphysical oscillations that may occur near transition boundaries in today's multiphase computer codes.
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