Wind machines are commonly used in vineyards in New Zealand during a radiation frost to draw warm air from above a crop and blow it over the crop to prevent frost damage. The primary source of noise produced by the wind machine has been identified as being aero-acoustic noise from the rotor. This paper describes a theoretical method for predicting both the broadband and tonal rotor noise. An empirical model that accounts for the effects of different blade tip geometries is derived from an experimental investigation and is combined with previously developed empirical methods to predict the broadband noise of the rotors. Several purely theoretical models are developed and used to predict the tone noise which is produced by rotating steady loading and thickness sources on the rotor blades as well as the interaction of the blades with the flow disturbance caused by the tower. The model is validated against measurements. As the method can calculate the noise level produced by a wind machine rotor very quickly, it is well suited for use in an optimization method where many different rotor designs are evaluated.
