High-Speed Shadowgraph Flow Visualization Studies on the Mechanism of the Onset of Screech and Its Attenuation in a Model Afterburner Test Rig

Abstract

Screech combustion instabilities continue to be one of the most detrimental and, in fact, fatal issues for the development of a high-performance afterburner. It is essential to study the underlying flow-physics related to the crucial thermo-acoustic coupling to acquire a predictive capability and to evolve a methodology for the attenuation of screech. A versatile test facility using a single V-gutter flame holder was used to generate the predetermined screech frequency of 2000 Hz in a controlled and sustained manner. The test facility had the capability to run the afterburner model under simulated inlet conditions of pressure and temperatures. The critical zone of flame stabilization near the V-gutter flame holder had complete optical access with quartz glass windows to study the vortex shedding phenomena during the afterburner operation. The critical operating parameters of the test rig were measured using a high-speed NI-based data acquisition system. Flow visualization studies using a high-speed shadowgraph technique was effectively used to understand the onset of screech. A FASTCAM SA-4 Photron high-speed camera was used in this experimental investigation. It was found that the cause for the onset of screech was the vortex shedding frequency from the flame holder locking on to the duct transverse acoustic resonant mode frequency.