Truncated method for propeller noise prediction up to low supersonic helical tip Mach numbers

The present paper addresses a simple truncation technique applied to cope with the sonic singularity so that noise from propellers can be computed in the subsonic as well as transonic and low supersonic domain at low numerical cost. Based on Farassat's 1A formulation of the Ffowcs Williams-Hawkings (FW-H) acoustic analogy, the present method computes the pressure signal for loading and thickness noise from steady RANS computations for arbitrary observer locations, by a retarded-time approach in the time-domain. For cases where the sonic singularity does not occur, the method consists of Farassat's 1A formulation; in cases where the sonic singularity occurs, it switches to an approximate prediction. The results obtained with this truncated method are compared with a series of experimental results over a wide range of operating conditions for two advanced propfan blade designs. The comparisons state on the validity of the method for the relative assess- ment of different designs. Being inexpensive and reliable, though approximate, it is suited for propeller optimization in a multi-disciplinary environment.