Numerical simulation of two-degree-of-freedom vortex induced vibration in a circular cylinder with OpenFOAM

• Author(s): Conceição, Pedro Daniel dos Santos
• Date: 2016
• Persistent ID: http://hdl.handle.net/10362/22139
• Origin: Repositório Institucional da UNL
• Subject(s): Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Mecânica
• Document Type: Master thesis
• Language: English
• Advisor(s): Conde, José
• Contributor(s): RUN

Description

Computational fluid dynamics tools are capable to simulate the influence of a fluid flow passing around an object. The ability to predict the impact of such flows on a specific product performance is time consuming and costly without some form of simulation tool. In fact, across a wide range of engineering areas, virtual development allows the reduction of the number of prototypes and less testing until a product is ready to the market. Therefore, it is important to provide computational fluid dynamics users with easy-to-use, robust, time-efficient and validated processes. Bearing this in mind, the current thesis studies the phenomenon of vortex induced vibrations simulating a flow around an oscillatory cylinder. A flow passing around a rhombic body originates dynamic forces which, consequently, induce a set of body movements that are well characterized in the literature. To perform the numerical investigation of this phenomenon was used the OpenFOAM, an opensource software which is numerically able to perform a detailed and accurate analysis of this complex phenomena. Given the few scientific studies about the vortex induced vibration phenomenon with two degrees of freedom, this thesis aims to validate the Open-FOAM software for this case study, providing the scientific community the validation of a new numerical tool for studies of this kind. With this goal, it was firstly performed a mesh independence study for a flow around a fixed cylinder where it was studied the influence of the mesh on the fundamental quantities, that is, the Strouhal number, St, the mean drag coefficient, CD,mean, and the root mean square of the drag, CD,rms, and lift, CL,rms, coefficients. Then, it was carried out the study of the flow around a cylinder with one degree of freedom. It was studied the response of the cylinder for two types of systems, mass-spring system and mass-spring-damper system for a mesh with a 2500D domain length. The obtained results where then compared with the data described in the literature for a 50D length mesh, allowing to infer which is the impact of the mesh size into the obtained results. Finally, it was studied the phenomena generated by a flow around a cylinder with two degrees of freedom. In order to validate this analysis, the obtained results for a 8D mesh were compared with the data described in the literature for a similar numeric study. The main difference obtained between both studies was the symmetry of the geometry of the cylinder’s oscillatory movement which was obtained by the current study whereas the comparative study showed an asymmetric movement of the cylinder. Given this data, it was hypothesised and proven that this fact was associated with the non-symmetry of the mesh used by the literature paper. Subsequently, it was studied the influence of the mesh refinement level in the response given by the cylinder with two degrees of freedom. It was also analysed how the size of the mesh domain influences the response given by the cylinder with two degrees of freedom. Particularly, it was compared the geometry of the oscillatory motion and the temporal evolution of the respective lift coefficient between meshes with 8D, 20D, 500D and 2500D size.