Title: Axially collapsing instability mode

Description: Shadowgraph images captured at 1,000,000 frames per second show an underexpanded impinging jet of air with a nozzle pressure ratio (nozzle stagnation pressure divided by ambient pressure) of NPR=3.5, and a non-dimensional impingement distance of Z/D=3 (Where Z is the impingement distance and D is the nozzle diameter). At this ratio the jet is influenced by a an axially collapsing instability mode which causes second, third and fourth normal shockwaves to collapse on top of one another. This mode is accompanied by an extremely loud, discrete tone.

Credits: Adam Risborg - Laboratory for Turbulence Research in Aerospace and Combustion, Department of Aerospace and Mechanical Engineering, Monash University

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Contributed By: Adam Risborg adam.risborg@gmail.com