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A hybrid model based on functional decomposition for vortex shedding simulations

Li, Q. (2017). A hybrid model based on functional decomposition for vortex shedding simulations. (Unpublished Doctoral thesis, City, Universtiy of London)

Abstract

Vortex-Induced Vibration (VIV) is one of the significant physics that encounter in the engineering practice. The good understanding of the structure response and technologies to suppress the significant vibration and undesirable forces induced by VIV is of vital importance for the entire design/planning procedure. However, for both the single-phase and multiphase flow, the main challenge is how to significantly improve the simulation efficiency and meanwhile maintain the accuracy.

This research aims to develop a hybrid model which can simulate VIV significantly more efficiently. A novel framework for a hybrid model which is based on the functional decomposition is proposed. The theoretical hypothesis of the hybrid model is that the viscous effect is only significant near the offshore structures or breaking waves, and may be ignored in other areas. In this model, all physical variables are split into two parts. One part is solved by a quasi-turbulent model in whole domain and the other part solved by using a residual turbulent model in a smaller domain. The two models are implemented simultaneously based on their respective meshes and time steps. Due to this feature, the techniques such as the sub-cycle strategy are employed for the improvement of the efficiency without the deterioration of the accuracy.

In this work, the equations and boundary conditions of the hybrid model for single phase and multiphase flow are derived. Corresponding algorithms and codes are developed using the open-source platform of OpenFOAM. The method is validated by simulating representative cases of flows past stationary and oscillating circular cylinder under various combinations of (Re, A/D, Fr) for single phase and of flows past stationary circular cylinder underneath an air-water interface for multiphase. It is demonstrated that the results of the hybrid model agree well with experimental data and with those obtained by using the original OpenFOAM. The investigation is also carried out on the efficiency of the hybrid model and indicate that the computational time of the hybrid model is significantly less than that of original OpenFOAM to obtain the similar results for the same cases. The investigation also indicates that the higher the Reynolds number, the larger the oscillation amplitude, the more computational time can be saved by using the new hybrid model. In some case, the hybrid model can save 80% of the computational time than using the original OpenFOAM solver.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TJ Mechanical engineering and machinery
Departments: Doctoral Theses
School of Mathematics, Computer Science & Engineering > Engineering
Doctoral Theses > School of Mathematics, Computer Science and Engineering
URI: http://openaccess.city.ac.uk/id/eprint/19667
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