A comparison of immersed boundary and body-fitted methods: Transient vortex shedding in elaborate bio-mimetic cylinders

Abstract

In this study, two contrasting computational fluid dynamics (CFD) methods are used to simulate flow around bio-mimetic cylinders. Cylindrical shapes are proposed to represent a cross-sectional view of complex geometries, such as cylinders with biofouling or cylinders with helical strakes. The non-conformal Cartesian immersed boundary method (IBM) and conformal curvilinear body-fitted method (BFM) are applied to solve the governing equations. A critical assessment of the accuracy and efficiency of IBM is presented by employing an open-source solver with similar discretization, algorithms, and properties. It has been found that IBM can reduce computation time by up to 49% for protrusions with different numbers of sides. Results show that IBM can reduce required computation time up to an outstanding 71% for protrusions with different heights. Results also indicate that transient duration doesn't significantly change the reduction trend in required computation time. For this reason, the onset of vortex shedding and eventually fully-developed flow takes place substantially sooner in IBM simulation than in BFM. It is also found that the height and shape of protrusions affect BFM performance but have no effect on IBM performance. This study proves that non-conformal IBM is a robust numerical approach when simulating vortex shedding in complex geometries.