湍流喷注噪声定律的发展

本文对流体动力噪声的Lighthill理论进行了讨论,并导出与其U⁸定律等值的压力定律,即噪声总功率为
$W = 8KD^2 frac{{(P _1 - P_0)^4}}{{rho 0c0P_1^2}}$
K即Lighthill常数,D喷口直径,P₁和P₀分别为气室和大气压力。这个式子适用于低压冷空气喷注。进一步推广,求得高压阻塞喷注的湍流噪声、温度不同、喷注媒质不同也都适用的定律,以90°方向、距离1米处的声压级表示（dB,0dB=20μPa）,得
$L = 80 + 10log $ frac{{(R - 1)^4}}{{R^2 - R + 0.5}}$+ 20log $frac{{TM_0}}{{T_0M}} + 20log d$
其中,R=P/P₀,d=直径（mm）,T,M为工作媒质的温度和分子量而T₀,M₀为室温及空气分子量。压力定律完全符合实验结果,它更便于在实际中应用。过去作者等提出的经验公式非常接近理论公式。

DEVELOPMENT OF THE LAW OF TURBULENT JET NOISE

Lighthill's theory of aerodynamic noise is re-examined,and an equivalent of his U8-law derived in terms of pressures. The total acoustic power of jet noise is expressed as
$W = 8KD^2 frac{{(P _1 - P_0)^4}}{{rho 0c0P_1^2}}$
K being the Lighthill's constant,D the diameter of the nozzle,P₁ the plenum pressure and P₀ the atmospheric pressure. This formula applies to cold-air jet at low pressures. Further development,the formula is generalized to high pressures,working material of molecular weight M at temperature T. Sound pressure level in the direction penpendicular to the jet is seen more exact to describe the field,and this at 1 meter from the nozzle is found as
$L = 80 + 10log $$ frac{{(R - 1)^4}}{{R^2 - R + 0.5}}$$+ 20log $$frac{{TM_0}}{{T_0M}} + 20log d$
where R=P₁/ P₀ and d=diameter in mm. The general formula reduces to the empirical formulae upon neglecting some small terms.