Noise Generated by a Centrifugal Fan without Scroll Casing : Effects of the distance between the leading edge of the blades and the wall of the mouthpiece, the geometry at the outlet of the bellmouth and the gap of the mouthpiece

Investigations of both noise and aerodynamic characteristics of a centrifugal fan without scroll casing were performed with respect to the effects of three parameters : (1) the distance between the leading edge of the blades and the inner wall of the mouthpiece, (2) the gap between the outer wall of the bellmouth and the inner wall of the mouthpiece and (3) the geometry at the outlet of the bellmouth. A formula was determined to predict the sound pressure level of turbulent noise from a centrifugal fan without scroll casing. It was shown that the total pressure and efficiency of the fan was reduced as the distance between the leading edge of the blades and the wall of the mouthpiece increased. If the geometry at the outlet of the bellmouth was straight, the sound pressure level appeared in the neighbourhood of 1.5 kHz and specific noise level was reduced as the gap between the outer wall of the bellmouth and the inner wall of the mouthpiece decreased. The agreement between the measured values and the predicted values of the sound pressure level of the turbulent noise was satisfactory.