Fluid-structure interactions

Fluid-Structure Interactions (FSI) constitute a broad range of problems where fluid loading results in structural response, which in turn affects flow development. For example, VIV discussed above constitute a special case of FSI. Our group is interested in FSI problems from the perspective of energy harvesting from fluid flows as well as cases where FSI can lead to the degradation of system performance. Small scale energy harvesting is of interest for powering sensors used in remote locations. For simplicity, robustness, and low cost, such an energy harvesting device can consist simply of a cantilevered strip of electroactive material which generates a voltage under applied deformation from fluid flow. We are using combined numerical and experimental approaches to analyze the interactions of coherent structures with compliant materials and determine the effect of flow and material characteristics on the energy transfer. Figures 7a and 7b show a numerical simulation of a vortex dipole interaction with a cantilevered plate, and figures 7c and 7d are the corresponding experimental visualizations.

7a.

Vortex dipole before engaging with cantilever plate

7b.

Vortex dipole after engaging with cantilever plate

 

7c.

Vortex dipole before engaging with cantilever plate

7d.

Vortex dipole after engaging with cantilever plate

 

Figure 7. Simulations (a) and b)), and flow visualization (c) and d)) of a vortex dipole approaching (a) and c)) and impacting (b) and d)) the tip of a deformable cantilevered plate.

A practical example of detrimental effect of FSI on system operation is that of a foreign object stuck in-between tubes within a steam generator. Here, flow induced vibration of such object can lead to local tube wear leading to costly shutdowns and repairs. Since the occurrence of such foreign objects in practical applications cannot be eliminated, it is of interest to know how the shape and size of the foreign object effect the wear rate at different flow conditions. This will help prioritize the retrieval of certain object types during Foreign Object Search and Retrieval Activities. Video 5 is a recording of a wire like object vibrating within the tube bundle.

 

Video 5. Experimentally recorded three-dimensional dynamic response of wire type foreign object inside peripheral tubes of normal triangular tube bundle.