Supersonic turbojet noise reduction

Observations and Large Eddy Simulations are presented of a supersonic jet from a nozzle representative of high-performance military aircraft such as the Saab Gripen. The nozzle has a design Mach number of 1.56 and is examined at its design condition with a surrounding secondary flow at Mach numbers of 0.0, 0.1 and 0.3. The nozzle is investigated in its unmodified state and also with the addition of chevrons and microjets. Detailed flow-field velocity measurements of the jets and far-field noise measurements are presented and the noise results are scaled to represent the effects of the chevrons and microjets on airport neighbors. Chevrons and internal fluidic injection by microjets each reduce the noise generated by the main jet. And substantially reduce the noise footprint around the airport. The numerical simulation technique, correctly predicts the flow and noise not only the baseline case, but also the noise reduction by both chevrons and microjects