Experimental study of aerodynamic noise from a double shaft fan

Noise pollution from wind turbines and blowers operating in the vicinity of residential buildings has in recent years been the focus of intensive research. This paper reports on the outcome of an experimental investigation to reduce the noise pollution through design, build and testing of a counter-rotating- double-row-fan with variable spacing. A single-row fan was selected as the benchmark fan. The mechanical noise and the background ambient noise were measured using the system operating with no-blades. The aerodynamic noise from the fan was then focused and air velocity, shaft-revolution, input-electric-power to fan, amplitude (dB) and Center Frequency (CF) in Hz of noise were measured using frequency-weighting of both "A" and "Linear". Coefficients of performance (COP), dB, CF, Tip speed ratio (TSR) were plotted for a range of spacing between two-blade-rows. It was noticed that double-shaft-fan relative to the benchmark single shaft fan has operated a) At a lower TSR due to division of the motor power between two shafts. b) At a higher COP of up to 18% due to a higher air velocity generated at the same motor power. c) Quieter at a lower dB (of up to 10 dB). d) At the minimum noise levels (80 dB) at the spacing of 15mm-to-25mm, using the "Lin"- weighting e) At the minimum noise levels (20 dB) at the spacing of 12mm-to 50 mm when measured at the "A"-weighting f) With no significant change in frequency of noise when operate at the same TSR. Copyright © 2012 by ASME