Experimental testing and modeling of a tethered spherical aerostat in an outdoor environment

This paper focuses on an investigation of the dynamic characteristics of a spherical aerostat on a single tether. A test facility was constructed to gather experimental data required to characterize the system. Our experiments were all in the supercritical range at Reynolds numbers greater than 3.7×105. The balloonʹs drag coefficient was extracted from position measurements. We find that the balloonʹs large oscillations and surface roughness, combined with the wind turbulence, result in a substantial increase in the drag coefficient. To further study the system, a numerical simulation was developed. The aerostat was modeled as a single rigid body attached to a tether, and subject to buoyancy, aerodynamic drag and gravity. The tether was modeled using a lumped-mass approach, which includes internal stiffness and damping. The dynamic simulation of the aerostat was obtained by setting up the equations of motion in 3D space and integrating them numerically. Finally, the model was validated through comparison with experimental data and a modal analysis was performed.