Roughness is added to the surface of a bluff body in a relative motion with respect to a fluid. The amount, size, and distribution of roughness on the body surface is controlled passively or actively to modify the flow around the body and subsequently the Vortex Induced Forces and Motion (VIFM). The added roughness, when designed and implemented appropriately, affects in a predetermined way the boundary layer, the separation of the boundary layer, the level of turbulence, the wake, the drag and lift forces, and consequently the Vortex Induced Motion (VIM), and the fluid-structure interaction. As such, the goal of surface roughness control is to decrease/suppress Vortex Induced Forces and Motion. Suppression is required when fluid-structure interaction becomes destructive as in VIM of flexible cylinders or rigid cylinders on elastic support, such as underwater pipelines, marine risers, tubes in heat exchangers, nuclear fuel rods, cooling towers, SPAR offshore platforms.
Researchers at the University of Michigan have developed a method to control VIM by introducing surface roughness control (SRC) on the structure with an overall goal to suppress VIFM. In particular, surface roughness is added to modify passively or actively the strength and 3-dimensional distribution of turbulence, which in turn affects vortex shedding, and subsequently vortex-induced forces and motion. The amount and distribution of turbulence in a flow past a structure is controlled by distributing the roughness on the surface of the body. Appropriate design of size and distribution of roughness reduces spanwise flow correlation length, as well as affects point of separation and turbulence shed into the wake. In addition, the system decreases the range of synchronization of VIFM of the structure in a relative flow.
Applications and Advantages
- Reduction of VIFM for various structure including underwater pipelines, marine risers, tubes in heat exchangers, nuclear fuel rods, cooling towers, SPAR offshore platforms.
- Composed of simple and readily available components.