Steady (DC) flow resistance measurements are performed to determine the “effective porosity” of the perforated face sheet of a single or double layer, resonator type acoustic liner after the completion of all manufacturing processes. Such measurements are specified to ensure that manufactured acoustic liners shall meet the acoustic design intent. Thus, the data obtained from DC flow tests establish the capability of the manufacturing processes in regard to the acoustic design of the face sheet. It has been established that there is a strong correlation between the discharge coefficient and the porosity of a perforated sheet. Previous correlation between the porosity and the discharge coefficient was based only on data measured with “punched” metallic perforated sheets. No attempt was made to investigate the effects of the additional processes that are involved in the fabrication of the liner panel. There are numerous items in the manufacturing process which affect the discharge coefficient. Therefore, it is very important to understand and to accurately determine the effects of these processes on the discharge coefficient of a perforated sheet during the different stages of manufacture of the liner panel. This paper will present the results of research, sponsored by NASA, on this subject.
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