| 摘 要： | Lighthill's theory of aerodynamic noise is re-examined,and an equivalent of his U~8-law derived interms of pressures.The total acoustic power of jet noise is expressed as W=8KD~2(p_1-P_0)~4/(σ_0c_0P_1~2)K being the Lighthill's constant,D the diameter of the nozzle,P_1,the plenum pressure and P_0 theatmospheric pressure.This formula applies to cold-air jet at low pressures.Further development,theformula is generalized to high pressures,working material of molecular weight M at temperature T.Soundpressure level in the direction perpendicular to the jet is seen more exact to describe the field,and this at lmeter from the nozzle is found as L=80+10 log(R-1)~4/(R~2-R+0.5)+20 log(TM_0)/(T_0M)+20 log dwhere R=P_1/P_0 and d=diameter in mm.The general formula reduces to the empirical formulae uponneglecting some small terms.
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