Home – Home – Jornals – Thermophysics and Aeromechanics 2004 number 4

Almost complete suppression of growth of the acoustic mode of disturbances in hypersonic boundary layers can be achieved by using special porous coatings absorbing sound. For testing conditions in hypersonic wind tunnels, rather smooth and thin coatings are required whose acoustic absorptivity is high in the high-frequency region and under low static pressure. In the present study, we examine acoustic properties of two types of coatings: with a regular pore structure and with chaotic porosity. By the acoustico-interferometric technique, we determined acoustic characteristics of both porous coatings in the region of audio frequencies and then calculated acoustic properties of the coatings in a broad range of frequencies. In performing the calculations, individual models for each type of materials were used. Direct measurements of acoustic absorptivity on aerodynamic models in the ultrasound range of frequencies under atmospheric pressure, and also the impedance of the coatings in the range of audio frequencies under reduced pressure well comply with model approximations.