Model position sensing method for low fineness ratio models in a magnetic suspension and balance system.

ABSTRACT

A new model-position-sensing method for the levitation of models with a low fineness ratio (ratio of the longitudinal length to the diameter) in a magnetic suspension and balance system (MSBS) is proposed. MSBS is an ideal model-support device for wind-tunnel testing, which enables the study of flow fields around blunt bodies without flow disturbances introduced by mechanical support devices, with the aerodynamic forces determined from the magnetic forces using a pre-calibrated relationship. The new method allows wind tunnel experiments without mechanical supports with a low fineness ratio model. This method adopts two line sensors placed parallel to the central axis of the model image and measures the position with a resolution finer than 0.06 mm or deg even for thin model geometries. In addition, measurement errors were reduced by correcting a second-order term in the depth direction of the camera. A low fineness ratio circular cylinder model was levitated following sensor calibration. The model was supported in conditions with and without freestream flow. This position measurement method was also applied to a reentry capsule model. The model was levitated while keeping its position and attitude stabilized near the origin.