Transverse Jet Shear Layer Instabilities and their Control

Professor Karagozian, Mechanical and Aerospace Engineering, UCLA

This talk will describe studies on the actively controlled gas jet injected transversely into crossflow, also known as the transverse jet. The transverse jet has widespread technological applications, ranging from dilution and fuel jet injection in gas turbine engines to thrust vector control systems for high speed aerospace vehicles. In our experimental studies, the dynamics of the jet actuation system are measured, characterized, and modeled, allowing a dynamic compensator or feedforward controller to be developed which permits the jet to be forced in a more precisely prescribed manner. Use of the controller allows for straightforward comparisons to be made among different conditions for jet excitation. Clear identification can be made of specific excitation frequencies and characteristic temporal pulse widths which optimize transverse jet penetration and spread through the formation of distinct, deeply-penetrating vortex structures. Exploration of these optimal forcing conditions has led to a fundamental examination of the transverse jet's nearfield shear layer instabilities. Unusual features of these instabilities are observed, whereby transition from convective to potentially absolute instability can occur under specific flow conditions. An understanding of these fundamental instabilities will allow us in the future to perform strategic control of the transverse jet for a wide range of flow conditions.