**Measurement of the 3D flow dynamics and associated fluid forcing in the wake of a stationary and tethered sphere in a uniform flow**

Flow around bluff bodies occurs frequently in industrial as well as environmental applications and remains one of the more complex flow types especially at higher Reynolds numbers. A general prototype of a bluff body is a sphere, the subject of interest in the present proposal. The flow around spheres has many interests both from the perspective of fluid- structure interactions as well as in the basic understanding of particle-turbulence interactions . When a sphere is immersed in a fluid with a relative velocity between the two, vortex shedding occurs beyond a certain threshold value of the Reynolds number, Re_{D} = *UD*/ν, where U is the relative velocity in the streamwise direction, *D* the sphere diameter and ν is the fluid kinematic viscosity. The vortex shedding frequency is characterized by the Strouhal number, St = *fD*/*U*, where *f* is the vortex shedding frequency. Little quantitative data is available on the intrinsically three-dimensional (3D) wake characteristics of a stationary sphere.

The research objectives:

- Measurement of the 3D wake structure of a stationary and a tethered sphere over a range of Reynolds numbers and mass parameters (tethered sphere only).
- Determination of the fluid forcing acting on the tethered sphere using the measured 3D flow fields. The results will be compared to direct measurements of the forcing on the sphere. This will provide insight into the relevant energy transfer mechanisms between fluid and sphere.

Students currently working on project: Tom David (MSc), Daniel Kovalev (MSc), Lior Eshbal (PhD)

Funding: Israel Science Foundation grant no.: 1596/14