抄録
Two support-interference-free measurements of aerodynamic forces exerted on an archery arrow (A/C/E) are described. The first measurement is conducted in a wind tunnel with JAXA's 60 cm Magnetic Suspension and Balance System (MSBS). The boundary layer of the arrow remains laminar in the measured Re number range (4.0 x 10^3 < Re < 1.5 x 10^4), and the drag coefficient is about 1.5 for Re > 1.0 x 10^4. The second measurement is performed by a free flight experiment. Using two high-speed video cameras, we record the trajectory of an archery arrow and analyze its velocity decay rate, from which the drag coefficient is determined. In order to investigate Re number dependence of the drag coefficient in a wider range (9.0 x 10^3 < Re < 2.4 x 10^4), we have developed an arrow-shooting system using compressed air as a power source. We attach two points (piles) of different type (streamlined and bullet) to the arrow-head and two kinds of vanes ('SPIN-WING-VANE' and 'GAS PRO') to the arrow-tail. The boundary layer is laminar for any combination, if Re is less than about 1.2 x 10^4. It becomes turbulent for Re larger than 1.2 x 10^4 and the drag coefficient increases to about 2.6, when the bullet point and 'SPIN-WING-VANE' are attached. In the same Re range, two values of drag coefficient are found for the streamlined point, of which the lower value is about 1.6 (laminar boundary layer) and the larger value is about 2.6 (turbulent boundary layer). In contrast, for 'GAS PRO' vanes, the boundary layer remains laminar at any Re considered. These findings confirm that both the point- and vane-shapes have a crucial influence on the laminar to turbulent transition of the boundary layer.
