Self-excited oscillations of two opposing planar air jets

Abstract

This paper investigates the self-excited oscillations of two co-planar air jets impinging on each other, referred to, hereafter, by opposing planar jets. The study is performed for a single jet thickness of h = 2 mm and a span-wise aspect ratio of 50. The effects of flow velocity of the jets and the distance between them are examined. The opposing planar jets are found to produce strong acoustic tones over a wide range of jet Mach number and separation distance. Phase-locked averaged particle image velocity measurements showed that the tone is generated by out-of-phase flapping oscillations of the planar jets. These oscillations are sustained by two effects. The first is the high stagnation pressure at the impingement region, which deflects the jets laterally in opposite directions away from their common centerline, while the second effect is the cross stream oscillating velocity in the entrainment regions around the jet exits, which forces the jets back towards their common centerline.