Federico Alzamora Previtali
Ansys Employee

You can use a Dynamic Mesh to move the sphere. You can either set a defined motion or let the movement of the sphere be dictated by the forces of the flow (Six DOF model).

12.6. Using Dynamic Meshes (ansys.com)

Chapter 14: Using Overset and Dynamic Meshes (ansys.com)

What are your modeling objectives once the sphere reaches the building?