To study the hydrodynamic characteristics of cylinders with different forms, numerical simulations of uniform flow around a four-arc smooth cylinder under typical subcritical condition Reynolds number RE = 3900 were carried out. The simulations were using SST-IDDES method. Comparisons between the four-arc cylinder and circular cylinder were investigated through the values of drag and lift coefficient, and Strouhal number. Wake flow of the four-arc cylinder is also analyzed. The results show that:
The average drag coefficient (Equation) of the four-arc cylinder is about 1.93 and the root mean square lift coefficient CLrms is about 1.19, which is larger than that of circular cylinder under the same Reynolds number;
The drag coefficient frequency is about 3 times of the lift coefficient frequency, and the fluctuation of drag coefficient and lift coefficient are not "regular". The reason was considered as superposition of shedding frequency of different vortex.
The Strouhal number ST is 0.167, which is smaller than circular cylinder flow, which means that the four-arc cylinder has a lower motion frequency in the cross-flow direction at the same Reynolds number.
Therefore, the increase of the drag coefficient and the decrease of the ST number of the four-arc cylinder contribute to its good stability and provide reference for underwater structures design, such as cables, chains and risers.
In ship and marine engineering structures design, there are many types of structures with arcs, such as risers, columns of tension leg platforms, and there are also some complex structures with multiple arcs, such as cables and chains, etc. Among them, these multi-circular arc structures have the characteristics of large scale and small feature length, which means even when the structures encounters a low Reynolds number, it can reach a high flow rate, and its hydrodynamic performance is significantly different from that of a cylinder.
