Isom's thickness noise for axial and centrifugal subsonic fans

The thickness noise predicted by the Ffowcs Williams and Hawkings (FW&H) equation depends on the normal velocity vnvn which is very sensitive to the meshing size. Isom showed that in a far field a monopolar source is equivalent to a dipolar source induced by a uniform distribution of the load on the entire moving surface. Consequently, the calculation of the thickness noise becomes completely independent of the normal velocity vnvn. Its expression, as suggested by Farassat, is for any moving surface. The main objective of this work is to determine a specific expression of Isom's thickness noise in time and frequency domains for axial and centrifugal subsonic fans. The proposed form of the thickness noise enables to highlight the effect of each geometrical parameter of the fan on the overall thickness noise, on the one hand, and presents a fast computational mean and low memory storage capability since the acoustic pressure in the frequency domain is calculated for only one blade, on the other.