Aerodynamic sound generation caused by viscous processes

With the aim of resolving some questions arising from previous studies by Morfey, Kempton, Hardin, and Kambe and Minota, the effects of viscosity on aerodynamic sound generation by unheated, low Mach number flow are investigated theoretically. First, an analytical solution in terms of a multipole expansion is derived by means of the method of matched asymptotic expansions. This solution is especially well suited to compare the results obtained by the various authors mentioned above. Second, an estimation of the importance of viscous effects on aerodynamic sound generation is given by which one can show that viscous effects have been overestimated in the past.