Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
Linear stability analysis of closure models for the 1D Two-Fluid Model: a focus on the velocity shape factor
Submission Author:
Rodrigo Luís Formosinho Castello Branco , RJ , Brazil
Co-Authors:
Rodrigo Luís Formosinho Castello Branco, Joao Carneiro, Angela Nieckele
Presenter: Rodrigo Luís Formosinho Castello Branco
doi://10.26678/ABCM.ENCIT2022.CIT22-0086
Abstract
The 1D Two-Fluid model is based on averaging processes to render the model tractable for industrial scale problems, resulting in information loss, which may render the standard model ill-posed. For vertical geometries, the model is unconditionally ill-posed, and closure relations play a key role, since they reintroduce missing physical parameters that may stabilize the flow and ensure well-posedness. The present work employs a new formulation for the liquid velocity shape factor CL for vertical annular flows based on the local velocity distribution. A liquid film velocity profile model is devised and integrated to obtain the CL formulation. Linear Stability Theory (LST) can be used to assess the hyperbolicity of a model by imposing small wavelength perturbations to the linearized version of the equation system and quantifying their growth. The novel model can be assessed in terms of its ability to induce damping of these disturbances. The viscous Kelvin-Helmholtz and the von Neumann stability analyses are performed to evaluate commonly employed closure models and the novel proposed formulation for the velocity shape factor. Results show that the novel model can guarantee well posedness of the linear system by introducing a growth rate plateau, blocking the unbounded growth of instabilities.
Keywords
1D Two-Fluid Model, Vertical Annular Flows, Momentum Flux Parameters, stability analysis, Assessment of closure models
