Self-Excitation of Small Plate Impingement Tones from Flat Plates with and without Coaxial Hole

摘要

Experiments are carried out to study the self-excitation of axisymmetric underexpanded sonic impinging jets on flat plates with and without coaxial hole. Feedback studies indicate that the self-excitation of secondary small plate impingement tones (S_2) involves an acoustic feedback to the nozzle. The role of an acoustic feedback to the nozzle in the self-excitation of primary small plate impingement tone (S_1) depends on the impinging plate diameter. The frequency of small plate tones (both S_1 and S_2) from plate with coaxial hole of diameter 0.5D_e is less than the plate without hole for the same nozzle pressure ratio (NPR) and nozzle-plate spacing. Small plate impingement tones (S_1 and S_2) are suppressed in the case of plate with coaxial hole of diameter 1.0D_e.