The discrete noise is an important component in aerodynamic noise of contra-rotating axial flow fans (CRAFF), which is caused by the contra-rotating of the two rotors. In the paper the turbulent flow field of a CRAFF has first been numerically simulated based on the unsteady 3D Reynolds-averaged Navier-Stokes equations, from which the fluctuating wall pressure with discrete spectrum were extracted and used as noise sources to calculate the sound field. Then the sound pressure level (SPL) of the discrete noise was obtained by solving the Ffowcs Williams-Hawkings (FW-H) equation, which was validated by experiments. It means that the presented method of numerical prediction of discrete noise radiated by a CRAFF is successful.
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