Seminar: On the Crackle Noise of Heated Supersonic Jets

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with "N-shaped" waveforms involving a shock-like compression, and thus is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent full scale testing has shown that the addition of chevrons to the nozzle lip can
significantly reduce crackle. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle, and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular,
shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this talk, we test this hypothesis through high-fidelity Large- Eddy Simulation (LES) of a hot supersonic jet of Mach number 1.56 and total temperature temperature ratio of 3.65.

About the Speaker

Dr. John T. Spyropoulos is an Aerospace Engineer at NAVAIR/Research & Development/Propulsion & Power Dept/Performance & Structures  (AIR 4.4.7), Patuxent River, MD; (1999-Present). He works on performance and operability analyses of propulsion systems and modeling and simulation technologies for inlets, nozzles and turbomachinery components. He has contributed on the development and execution of a USN-wide program on exhaust jet noise reduction for tactical aircraft; (2004-2012). He has also worked for the Joint Strike Fighter Program Office (JPO)/ Propulsion IPT and Air Vehicle IPT; (2002-2014) as Computational Fluid Dynamics (CFD) subject matter expert; inlet/engine integration; steam ingestion and Hot Gas Ingestion (HGI) operability; Lift Fan aeromechanics and operability. He is AIAA Senior Member and a ASME International Gas Turbine Institute Member. Education: PhD Aeronautics & Astronautics, 1999 ;MSc Applied Mathematics ,1994; MSc, Mechanical Engineering, 1983; BSc, Mechanical Engineering, 1981 all from Purdue University, W. Lafayette, IN.

Hosted by Professor Datta Gaitonde