The Development of a Passive Magnetic Levitation System for Wind Tunnel Models

Rolling road testing at model scale is most often done using a wide-belt to provide a good simulation of the relative movement between the vehicle and the road. This generally requires the use of struts to hold the model under test in position, and the aerodynamic interference of these struts can be significant. A non-intrusive method of model testing would therefore be desirable. Many alternatives for reducing or eliminating the strut interference have been considered; of these magnetic levitation has been identified as the approach with the greatest ultimate potential. Previous attempts at magnetic levitation within the aerospace community have been restricted to small scale due to the large magnetic air gap required between the model and the tunnel walls. For ground vehicles, however, the gap between the underside of the model and the tunnel floor is relatively small, providing an opportunity for magnetic levitation on a practical scale. This paper documents the design and development of a magnetic levitation system to support ground vehicle models in a wind tunnel over a rolling road at up to 40% scale. The system uses a combination of permanent magnets, electromagnets and bulk type II high temperature superconductors (HTS). The superconductors provide intrinsic damping in order to make the system robust with respect to power / computer failure which could otherwise cause a sudden loss of levitation stability.