UNSTEADY-FLOW IN DIFFUSERS

The flow in a diffuser is unsteady in the range of optimum pressure re covery; diffusers can therefore be a major source of noise in pipework systems. A theory is developed to predict the frequency of this noise and good agreement with experimental results, for both conical and re ctangular diffusers, is demonstrated. The acoustics of the duct to whi ch a diffuser is connected are found to have a crucial effect on the u nsteady flow within the diffuser, a point which has been overlooked pr eviously in the literature. Once this is recognized, it is possible to reconcile experimental results for air and water diffusers.