Study on aerodynamic force acting on a sphere with and without boundary layer trips around the critical Reynolds number with a magnetic suspension and balance system |
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Authors: | Hideo Sawada Shinichi Suda |
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Institution: | (1) Low-Turbulence Wind Tunnel Laboratory Liaison Office, Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan;(2) Technological Planning Group, InterDesign Technologies, Inc., 3-43-16, Shiba, Minato-ku, Tokyo 105-0014, Japan |
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Abstract: | Aerodynamic force acting on a sphere for five kinds of boundary layer trips around the critical Reynolds number, together
with the force on a smooth sphere, was successfully measured. This was achieved using JAXA’s 60-cm Magnetic Suspension and
Balance System after performing detailed simulations and adjusting the sphere mass and its control parameters. The minimum
drag coefficient of a smooth sphere was evaluated around 0.19 in the support-interference-free condition. No hysteresis was
observed for the drag coefficient in the critical range for tested sphere with boundary layer trips. Using three serially
connected 2nd-order Butterworth low-pass filters, an inertia force oscillating at less than 15 Hz was evaluated from the measured
model position, and the unsteady aerodynamic force acting on the sphere was also evaluated with reasonable accuracy. Two kinds
of oscillatory aerodynamic forces appeared in the critical range depending on the sphere surface condition: a force rotating
around an axis parallel to the uniform flow for both a smooth sphere and a sphere with axially symmetric 0.17-mm-high backward
step, and an oscillating force in the plane including the axis parallel to the flow for a sphere with axially symmetric step
implemented with 0.35–mm-thick tape with wrinkles acting as small vortex generators. There was also observed a force irregularly
rotating through less than 180° in the range about a sphere axis parallel to the flow for a smooth sphere in the supercritical
range. |
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Keywords: | |
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