Non-intrusive support of ground vehicle wind tunnel models through superconducting magnetic levitation

Abstract

Wind tunnel testing of racing cars is performed with a moving ground plane to take into account the downforce generated by the low ground clearance of these vehicles. Struts and wheel stings, mounted from the roof and walls of the tunnel, are used to hold the vehicle in position within the test section. These supports disrupt the airflow around the model, thereby deviating from on-track conditions. Where the vehicle's aerodynamics are already highly refined, the effects of subtle shape changes such as those made in Formula 1, may be much smaller than the errors introduced by the supporting struts. Support interference can also lead to incorrect optimisation of aerodynamic elements. A magnet will stably levitate over a High Temperature Superconductor (HTS) cooled below its critical temperature. The magnetic flux of the magnet becomes pinned within the bulk HTS microstructure in the form of individual flux quanta, each of which is surrounded by a current vortex at sites of imperfection in the superconducting matrix. This mechanism formed the basis of the superconducting pod which achieved stable passive levitation. Finite element analysis simulation was used to optimise the effectiveness of the electromagnets providing a restoring force to the levitating magnets. To augment the superconducting levitation, without introducing excessive instability to the levitation, the magnetic rail was invented. Traverses of both the superconducting pod and the magnetic rail were performed to map the forces each produced. The feasibility of a non-intrusive method of supporting ground vehicle wind tunnel models has been investigated. The Superconducting Magnetic Levitation System combines the inherent stability and damping of superconducting levitation with the high ground clearance of magnet only levitation. Stable passive levitation has been achieved, with six degree of freedom control. The system uses a combination of type II high temperature superconductors, rare earth permanent magnets, and electromagnets to support a model under test. The final prototype of the superconducting magnetic levitation system was designed to support a 40% scale Formula 1 model. The system was capable of supporting 250N of downforce on top of- the weight of the model and 90N of drag at ground clearances comparable to 40% scale Formula 1 clearances. The Superconducting Magnetic Levitation System is the largest wind tunnel magnetic levitation system in the world and has been successfully tested at speeds of up to 20ms"' in the Durham 2m wind tunnel.