Parametric studies on porosity and aspect ratio of ultrasonically absorptive coating are performed using a theoretical model. The fluctuation of reflection coefficient is caused by the reinforcement and cancellation of bottom reflection. At altitude H* =30km, the reflection coefficient decreases clearly with increasing porosity. The fluctuation of reflection coefficient decreases with decreasing aspect ratio. This phenomenon reveals that the bottom reflection attenuates due to the high viscous dissipation for low aspect ratio ultrasonically absorptive coating. The linear stability theory is employed to analyze the growth rates of Mack mode developing on flat plate and ultrasonically absorptive coating. The growth rates from present method agree well with the existing data. In contrast to the UAC of n = 16, the fluctuations of pressure and vertical velocity for the UAC of n = 8 are less concentrated, which corresponds to a lower growth rate. A computational aeroacoustics method is implemented based on a 2-2 MacCormack scheme to explore the reflection phenomenon of acoustic wave. The acoustic wave reflections for flat plate and ultrasonically absorptive coating are successfully captured by current computational aeroacoustics method.
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