The wings of birds and insects often create an unsteady flow by their flapping and dynamic stall is used actively for landing or in low-speed flight. The flapping motion of the wings of insects consists of a combination of heaving (vertical movement in a forward direction), lead-lag (back-and-forth movement in a forward direction) and feathering (rotational movement around a feathering axis). Heaving is a fundamental motion of insect flight because it generates thrust in the air flow caused by the forward motion. The aerodynamic characteristics at low Reynolds number such as insect wings are different from aircraft, and little research has been conducted on the subject. The steady aerodynamic characteristics of the wings at low Reynolds number (Re less than or equal to 10,000) have therefore been examined with wind tunnel tests and free-flight tests of gliders. This time the unsteady aerodynamic characteristics of the wings were studied by applying heaving and feathering motion to the test wings in the flow of wind tunnel. One of the problems with such unsteady experiments of the heaving motion is that the wing moves with a large inertial force. A measuring device was therefore contrived to reduce the inertial force to the greatest extent possible. Rectangular wings, with various sections made of balsa wood or thin carbon fiber plate to make the wings lighter, were then tested. The aerodynamic characteristics of the wings can be considered as two dimensions because the aspect ratio is 6. Reduced frequency is considered to be 0.3 or less and the Reynolds number is about 8,000. An experimental test of feathering motions for the thin flat plate wings was performed and compared with the result of the heaving motion. Experimental tests of combined heaving and feathering motions were also conducted. The two-dimensional unsteady aerodynamic characteristics of wings at low Reynolds number were examined through a series of experimental works.
低レイノルズ数における翼の2次元非定常空力特性の実験的研究
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