Abstract
Aerodynamic torques about the vertical major axis of each of three rotating oblate spheroids (axis ratios 0.50, 0.67, and 0.79) with smooth surfaces were measured in a horizontal wind tunnel as a function of Reynolds number (4 × 104 < Re < 3 × 105) and rotation rate. Rotations were either about the vertical axis or the minor axis which was held inclined to the mean air flow at several fixed angles. Spin about a minor axis only shifted critical Reynolds numbers to lower values. Spin rates corresponding to Strouhal numbers less than 0.1 at Reynolds numbers less than 1.5 × 105 had no effect on the aerodynamic restoring torque. Each of the three spheroids autorotated at frequencies with Strouhal numbers of approximately 0.15. For rotations at Strouhal numbers less than 0.04, the average nonconservative torque was less than 10% of the maximum static torque. Hence, these experiments establish the range of applicability of a quasistatic approximation for the aerodynamic torques on smooth oblate spheroids. They also give necessary basic data for the general treatment of aerodynamic motions of this type of body in free fall.
Published Version
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