高次스펙트럼을 利用한 機關 排氣系의 非線型 脈動壓力 解釋에 관한 硏究

The engine exhaust noise is mainly made of the pulsating gas flow and pulsating pressure at a very high pressure level. Frequently, this pulsating pressure level is out of the pressure level range which the linear acoustic theory is applicable. The conventional prediction method which is based on the linear acoustic theory gives an overestimate in comparison with results measured in operating engines. This paper, as the first step for solving this problem, proposes a non linear effect of pulsating pressure waves. The phenomenon proposed here is identified by using of higher order spectrum(bicoherence),