and the ratio of the wake generated field (9.24) to the field (9.23) 

 which would exist in the absence of the wake is (since q > k ) roughly 



it) 



(9.25) 



This shows that if the plate wave travels at speed w/q between the flow 

 speed and the sound speed, the wake contribution to the far-field is 

 negligible. If, on the other hand, the plate wave travels sore slowly 

 than the flow speed, Mq/k exceeds unity and the sound field when the 

 Kutta condition is imposed exceeds that in the absence of any wake. 



This is not to be regarded as a general conclusion, for in other 

 problems the wake sound very nearly cancels the primary edge field. That 

 in fact happens here, for when q becomes close to k /M it can be seen 

 that the fields (9.23) and (9. 24) have small but equal and opposite 

 values. Whether the extra wake field domiuates, or mainly cancels 

 the primary edge sound field thus depends very much on details of the 

 basic excitation. 



70 



