The Near Noise Field of Static Jets and Some Model Studies of Devices for Noise Reduction

Choked operation of model jets with unheated air indicates the appearence of a discrete-frequency component of very large magnitude. Shadowgraph records of the flow show that this condtion is associated with the appearance of flow formations suggestive of partly formed toroidal vortices in the vicinity of the shocks. Elimination of these formations is found to eliminate the discrete component and thereby to reduce the overall noise level.