Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Validation and Analysis of Turbulence Modeling in Secondary Flow Conditions using OpenFOAM
Submission Author:
Ana Cristina Neves Carloni , SP , Brazil
Co-Authors:
Ana Cristina Neves Carloni, Kevin de Conde, ALUISIO PANTALEAO
Presenter: Ana Cristina Neves Carloni
doi://10.26678/ABCM.COBEM2021.COB2021-0086
Abstract
As a solution to the closure problem, turbulence models were developed to propose approximations for the unknown correlations by associating them with the flow’s known properties, to equal the number of equations and the unknown terms. Despite the known limitations, eddy-viscosity models are usually used in industrial applications, once they do not spend substantial computational resources compared to LES and DNS approaches. The present work proposes to analyze five RANS turbulence model’s performance in predicting an internal single-phase incompressible turbulent flow through a 90-degree-bent pipe with a circular cross-section, using the software OpenFOAM. The flow is characterized by Reynolds number Re = 24000, Dean number De = 13500 and bend ratio Rc/D = 1.58. Such geometry and flow regime, although simple, aim to present challenging phenomena from a turbulence modeling standpoint, such as the presence of adverse pressure gradients, high streamline curvature, and secondary flow. The purpose is to determine the most appropriate among the proposed RANS turbulence models envisioning further application in multiphase flows. Validation of the simulations’ setup was performed by comparison with log-law results and, additionally, the results arising from these computational simulations were compared with LES and experimental results from literature. Based on their formulations, it was analyzed the proposed turbulence models’ performance, which are standard k−ε, realizable k-ε, RNG k-ε, k-ω SST and Shih’s nonlinear k-ε. Results show that the mean velocity profile downstream of the bend predicted by the k-ω SST model oscillates and tends to the standard k-ε velocity profile above y+=394.5. Quantitative analysis of the blending function F1 shows that the k−ω SST model also applies exclusively the standard k-ε model from y+=394.5 ahead, which may support its behavior tendency. Besides, all of the flow phenomena are not fully reproduced by a unique turbulence model, hence, a RANS turbulence model should be chosen based on both the envisioned application and the prediction priority of physical phenomena. Envisioning to determine the characteristic force of fluids interaction in multiphase turbulent internal flow in a pipe elbow, one concludes that, among the proposed models, the k-ω SST model is the most appropriate one to predict the velocity profile in the region of streamline curvature, whereas in the presence of high adverse pressure gradient the most appropriate turbulence model is the realizable k-ε. Results suggest that the unsteadiness of turbulence may be more relevant than the anisotropy to describe the flow’s dynamic.
Keywords
Turbulence Models, Secondary-flow, 90-degree bent elbow, Pipe bend
