Noise Reduction of a Vacuum-Assisted Toilet

Flushing of an aircraft vacuum-assisted toilet generates high noise levels that can be disturbing to both users and those seated near lavatories. This paper describes the results of an investigation into reducing the aeroacoustically-generated noise. Three stages of noise can be correlated with three flush valve conditions during the flush cycle: an initial noise level peak associated with the flush valve opening, an intermediate noise level plateau associated with the valve being fully opened, and a final noise level peak associated with the flush valve closing. It was hypothesized that increasing the distance between the flush valve and the bowl and increasing the bend radius of the attachment at the bowl exit reduces overall noise levels. These modifications resulted in a 13 to 16 dB reduction in the noise radiated from the bowl during the valve opening and closing in addition to a 5 to 10 dB reduction in the noise radiated from the bowl during the open valve condition. The paper also discusses intermediate results that show the effects of varying tube length and bend radius on the radiated sound levels which gives insight into the noise generation mechanisms.