Use of the wave directional frequency response function (dFRF), which is composed of conventional frequency response functions, is proposed for identification of the forward and backward travelling wave modes of isotropic rotating disks. The driving point dFRF, which is a weighted sum of complex wave dFRFs defined in the complex wave coordinates, is also derived for separation of the forward and backward travelling wave modes in the frequency domain. Numerical examples of rotating disks are treated to demonstrate the analytical developments. Experiments with a laboratory rotating disk are also performed to verify the theoretical findings.
