Design of a Magnetic Suspension and Balance System for the Princeton/ONR High Reynolds Number Testing Facility

Princeton University is currently constructing a specialized wind tunnel, the Princeton/ONR High Reynolds number Testing Facility (HRTF) to be used for aero/hydrodynamic testing of submersible shapes. The facility will operate at very high pressures, up to 230 atmospheres, and relatively low velocities. Old Dominion University is responsible for the design and commissioning of a Magnetic Suspension and Balance System (MSBS) for use with the HRTF. The HRTF design and operational characteristics will be briefly described, then the paper will concentrate on the design challenges faced by the MSBS. The most unusual problems are related to the fact that the electromagnets will be located outside the wind tunnel pressure shell, with position sensing and other hardware inside. The test section is constructed of stainless steel, so eddy currents generated by unsteady magnetic fields are a serious concern. It is shown by analysis and confirmed by measurements that the system is practical, provided the eddy current effects are properly modeled and accounted for in the control system design. Due to restricted access to the interior of the tunnel, the position sensing and control systems must be configured so as to reliably suspend models for long periods of time, with a variety of aero/hydrodynamic tests conducted in sequence. This leads to a relatively conservative choice of system configuration and hardware. The general design of the MSBS will be presented and plans for completion, commissioning, calibration and operation of the facility will be reviewed.