Noise and Efficiency of Axial-Flow Fans

A test apparatus was constructed and instrumented for testing tractor engine cooling fans in an environment simulating actual operating conditions. Tests were conducted to investigate the influence of the blade pitch angle, blade camber and fan rotational speed on the air delivery performance, the input power requirements, and the sound power radiated.

Prediction equations for the pressure coefficient and the power coefficient as functions of the flow coefficient and the blade pitch angle were developed for each level of blade camber. Prediction equations for the overall acoustic parameter as functions of the flow coefficient, Reynolds number and the blade pitch angle were also developed.

A comparison of the prediction equations for the pressure coefficient, the power coefficient and the overall acoustic parameter indicated that the efficiency and the range of efficiency decreased as the blade pitch angle increased. High values of the overall acoustic parameter were associated with higher Reynolds numbers and higher blade pitch angles. The comparison procedure should make possible the selection of a tractor radiator cooling fan based on noise production as well as air movement and efficiency.