Abstract:

ESDU 00012 introduces a computerized method for estimating the sound power attenuation of absorbent linings in constant section straight circular ducts with axial flow. The method is based on a theoretical model that takes the velocity profile across the duct, assumed constant axially, into consideration. The program permits the user to output results in various degrees of detail. It also allows the user to perform calculations for a variety of modal pressure distributions including one which is thought to approximate the tonal fan noise due to rotor-stator interaction. The format of the input file is explained and a second ESDUpac, B0012, facilitates its construction. The input requires values for the normalized acoustic impedance for each lined section and, for low Mach numbers, values may be taken from ESDU 74003 and ESDU 74004, while for higher Mach numbers the liner manufacturer will need to be consulted. A worked example illustrates the various features of the program.