280 Lecture 15 
It is impossible to describe here all the investigations of interest to naval 
research workers. Therefore discussion will be confined to three aspects of our 
work at Southampton University, viz: 
1. The nature of boundary-layer pressure fluctuations and the effect of 
single roughnesses 
2. The radiated sound from a small flat plate 
3. The modes of oscillation of structures, the acoustic damping achieved, 
and the reradiated noise problem 
In addition, the significance of the investigations to the field of underwater noise 
will be illustrated by some simple calculations of radiated and self- noise based 
on the above and other investigations. 
15,2, BOUNDARY-LAYER PRESSURE FLUCTUATIONS 
We are interested in measuring the pressure fluctuations on the surface of an 
aircraft both at subsonic and supersonic speeds in order to ascertain the fluctu- 
ating loads occurring on it and in order to obtain the information necessary to 
calculate the noise radiated from the surface as a result of these fluctuating 
forces. It has been necessary to measure not only the rms pressure at the skin, 
but also the areas over which these pressures are correlated and the power 
spectrum of the fluctuating pressures relativetoaconvected frame of reference. 
Fig. 15.1. Boundary-layer wind tunnel. 
