The effect of grazing mean flow on acoustical character of micro-perforated panel absorber

There are three effects of grazing mean flow on acoustical character of micro-perforated panel absorber(1) on radiation impedance of orifice,(2) on acoustical impedance of construction at sound wave angle incident,(3) on sound propagation property in duct lined construction.Based on acoustical fundamental principle,these effects were analyzed respectively,and relative formulas were derived.Some qualitative tendencies were shown that radiation impedance of orifice,value ofξin function coth(ξ) which estimates cavity impedance,and transmission loss in lined duct all will decrease with flow speed increases as well as the resonant frequency will move to lower frequency caused Doppler effect, when sound wave propagation direction is same with flow direction.The discussion was also supported by a relative experimental study.