‘Butterfly acoustical skin’ – new method of reducing aero acoustical noise for a quiet propeller
An experimental investigation was conducted on the effect ‘butterfly acoustical skin’ (metallic version of the lepidopterans scale coverage) on the acoustic performances of two - bladed propeller (diameter of 1200 mm, airfoil sections of NACA 2415, rotating speed of 1780 rpm, Re ≈ 2 × 105) in a low – speed straight through a wind tunnel. Attention was initially directed to this problem by observation of the porous scales and porous scale coverage of lepidopterans as well as other studies indicating the noise suppression of flying lepidopterans by wing appendages. The property of the moth coverage allows these insects to overcome bat attacks at night. These appendages are very small (size: 30 – 200 μm) and have a various porous structures. I discuss both many different micro – and nanostructures of the porous scales, and many differences in details among various structures of the porous scale coverage of lepidonterans. I consider here only porous scales of butterflies Papilio nireus, Nieris rapae, Deelias nigrina, male Callophrys rubi, male Polyommatus daphnis, butterfly Papilio palinurus as well as porous scale coverage of cabbage moth, moth of Saturniidae family and moth of Noctuoidea family. The evolutionary history of lepidopterans and the properties of lepidopterans scale coverage is briefly discussed as well as different methods of reducing aero acoustic noise of aircrafts.
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