Experiments on effective source locations and velocity dependence of the broad band noise from a rotating rod

Effective acoustic source positions (observed from the far field) have been located for the broad band noise from a cylindrical rod rotated about its mid-point by measuring the cross spectral density function of two microphone signals on the axis of rotation. Local source position Strouhal numbers could thereby be calculated. On the basis of acoustic power measurements it was demonstrated that the noise may be normalized on a rod tip Strouhal number basis, and that the velocity exponent is nearly constant when plotted against this parameter. The results indicate that vortex shedding like that for stationary cylinders in a cross flow (occurring along the outer $\text{1}\text{3}$ of the rod for a rotational speed of 1000 rpm) is responsible for the high levels of broad band noise in a major peak region. Sources influenced by harmonics of the rod passing frequency were found for frequencies lower than the vortex shedding ones. At higher frequencies broad band noise was found to be emitted from the rod tip area.