Evaluation of the influence of the number of blades and diameter on propeller noise

The article presents the results of computational and experimental research of the effect of the number of blades and the diameter on the noise of the propeller operating at Reynolds numbers of more than 106. It is shown that an increase in the number of blades while maintaining the aerodynamic and geometric similarity of the propellers and constant Mach number of the circumferential velocity leads to significant reduction of aerodynamic load noise. At the same time the displacement noise and the broadband noise increase insignificantly. Expressions are proposed that can be used to assess the effect of the diameter and the number of blades on the tonal noise and the noise of the trailing edge of the propeller provided the propeller thrust is constant. Measurements of the acoustic characteristics of light aircraft Yak-18T with two- and three-bladed propellers, MAI-223M and the F30, performed at the local aerodrome in static conditions qualitatively confirmed the estimates of the effect of the diameter and number of blades on the propeller noise. Increasing the number of blades leads to a noticeable decrease in the acoustic efficiency of engine-propeller power plants