Introduction of 1-m MSBS in Tohoku University, New Device for Aerodynamics Measurements of the Sports Equipment

Abstract

Support interference in wind tunnel testing is an unavoidable effect. It is difficult to measure the aerodynamic force acting on a model such as a ball owing to this effect [1]. A magnetic suspension and balance system (MSBS) suspends the model without any mechanical supports by using magnetic force, and at the same time, can measure the aerodynamic force acting on the model. The 1-m MSBS, located at the Institute of Fluid Science, Tohoku University, is the world's largest MSBS. It has a 1-m-wide octagonal cross section. A sphere is taken as the experimental object, and the results of the aerodynamic force acting on it are presented. The diameter of the sphere is 150 mm, and its blockage ratio is 2.1%. The experiment was conducted at Reynolds numbers ranging from 0.5 × 10 5 to 4.7 × 10 5 . It clearly shows the drag crisis at approximately Re = 3.7 × 10 5 , and the fluctuation of the sphere abruptly increase around this region.

Measurement of aerodynamic force and moment acting on a javelin using a magnetic suspension and balance system

“…For example, the two donut-like air core coils (#0 and #9) in the flow direction work to counterbalance the drag. The other eight coils are iron core coils, which efficiently generate a magnetic field by connecting coils # 1 to # 4 and # 5 to # 8 with the yoke to form a magnetic circuit 11 . A power amplifier is attached to each coil, each of which can pass a current of up to 150 A.…”

The Oxford Magnetic Suspension and Balance System: a Brief History & Development Status

“…Calibration of the drag coils related the required current in the coils to a known load applied to a suspended model. Although typical for MSBSs [22][23][24], this relation is in contrast with the method used on the first generation balance whereby the magnetic flux gradient was independently measured and calibrated [4]. It is unclear which method is superior.…”

Reaction Force-Based Position Sensing for Magnetic Levitation Platform with Exceptionally Large Hovering Distance

“…The second type of MLP features a large air gap [12][13][14][15][16][17][18] and is applied, for example, in wind tunnels, where large distances between the object under test (or mover) and the surrounding levitating system are required. The largest structure of this kind offers a cylindrical space with a diameter of 1 m [19], where the levitated object under test is equipped with permanent magnets on the inside, and electromagnets (EMs) are placed around it, enabling contactless magnetic suspension and balance with the help of optical sensors for position control [20]. Accordingly, any other mechanical structure needed to hold the object under test in place can be omitted, avoiding changes in the airflow around it.…”