title: The connection between sound production and jet structure of the supersonic impinging jet.
abstract: An experimental investigation into the sound-producing characteristics of moderately and highly underexpanded supersonic impinging jets exhausting from a round convergent nozzle is presented. The production of large plate tones by impingement on a square plate with a side dimension equal to 12 nozzle exit diameters is studied using random and phase-locked shadowgraph photography. Discrete frequency sound is produced in the near-wall region of the jet when a Mach disk occurs upstream of the standoff shock wave. Tones cease when the plate distance is approximately 2.2 free-jet cell lengths and the first and second shock waves are located in the free-jet positions. The production of impulsive sound appears to be associated with the collapse of the standoff shock wave during a portion of the oscillation cycle. Results from unsteady plate-pressure measurements indicate that plane-wave motion occurs in the impingement region and a secondary pressure maximum is observed on the plate adjacent to the flow region where sound appears to originate.
authors.affiliation: Mechanical Engineering Department, Kettering University, Flint, Michigan 48504-4898, USA.
authors.forename: Brenda
authors.initials: B
authors.lastname: Henderson
mesh_terms: D000401:Aircraft; D011312:Pressure; D013016:Sound; D014465:Ultrasonics