Estimating surface pressure on flexible structures subjected to flow-induced vibrations

A conventional flag is placed downstream of the inverted half cylinder to study pressure over the flag's surface due to fluid-flexible body interaction between the flag and the vortices generated by the half cylinder. An immersed boundary method provides a reliable and fast solution to the fluid-structure interaction problems, albeit with limitation. One such limitation is the accurate pressure profile over the Lagrangian grid, i.e., the structure boundary. A pressure prediction algorithm is proposed which couples with the improved immersed boundary method to predict pressure over flag's surface. The effect of flow patterns on flag's surface pressure is studied by varying flag's distance from the bluff body. The pressure results are analyzed as negative and positive pressure fluctuations from the assigned reference pressure in the far field. Results show high flag surface pressure at a smaller stream-wise distance. A subsequent decrease in flow pressure is observed, when the stream-wise distance is increased. Changing span-distance shows that the highest pressure occurs at Gy = 0.25 with a significant drop at span positions of 0 and 0.5. The average pressure over the flag's surface is also affected by the vibration modes and the vortex shedding from the surface of the flag. The deflected mode appears at a smaller stream-wise distance accompanied by additional vortex shedding from the flag surface resulting in a high average pressure. Whereas biased and conventional flapping modes appear as stream-wise distance is progressively decreased resulting in reduced average pressure. Hydrodynamic analysis shows that the vortices originating from the bluff body and their subsequent interaction with the flag serve as the primary source of pressure fluctuations resulting in a change in the pressure profile over the surface of the flag.