‘Carousel’ goes automatic

Abstract

Some theoretical results are presented for the mixing of coaxial streams of fluid boundede by a tube of finite length. From these it is possible to make an estimate, based on dimensional analysis, of the proportion of (broad-band) aerodynamic noise generated relative to that from the unmodified primary stream. This approach is applied to the mixing of flows in an ejector system, when a circular nozzle discharges into a set of cylindrical shrouds under a range of operating conditions. The estimated attenuations are compared with the actual figures obtained by experiment on a model rig. The situation has been made more complex by the proven existence of several noise sources, both for subsonic and supersonic flow within the ejector. It is concluded that the optimum length of ejector to act as noise suppressor with a plain primary nozzle is of the order of 20 times the diameter of the latter. An experimental investigation into the aerodynamic behaviour of these ejectors has been undertaken by Reid -xb[1], and the majority of the acoustical measurements have been given elsewhere by the present author -xb[2].