Control of Instability Transition in Transverse Jets

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Jets injected perpendicularly into a cross-stream, or transverse jets, exist both in nature and in a wide range of engineering applications. For example, transverse jets are used to control fuel-air mixing and cooling of turbine blades in gas turbine engines for aircraft as well as in stationary power plants. Such jets are also used for fluid injection in liquid rocket engine pre-burners and in environmental control systems. A volcanic plume may also behave like a transverse jet in a windy environment. Controlling and optimizing transverse jet behavior can improve fuel efficiency, control vehicle performance, and potentially reduce environmental impact, all of which are important economic, energy and national security goals. Recent experimental studies have demonstrated the value of actively controlling transverse jets, or controlling the flow immediately exterior to the jets, in order to improve performance for a range of flow regimes and applications. The proposed experimental studies in this project are designed to focus, in greater detail, on the fundamental physics of transverse jet instabilities. This include studying their dynamical character, how they arise, and hence how they may be actively controlled in a robust manner. The broader impacts of the proposed studies will expand beyond practical applications and graduate level research. It will include undergraduate research training, community outreach, and summer laboratory experiences for local high school and community college students and potentially undergraduates at other universities. The proposed experimental research activities will examine shear layer instabilities and asymmetries that naturally form in the transverse jet flow field, and how different approaches for excitation can control jet behavior tailored to different classes of applications. In addition to fundamental exploration for the single, nozzle-generated transverse jet, it is proposed to examine an alternative configuration, a coaxial jet in crossflow. This will determine the effects of a new modality for control of shear layer instabilities via creation of counter-current shear using suction or blowing in the outer annular section of the coaxial jet. The studies will also build on recent discoveries of dynamical lock-in, quasi-periodicity, and regular patterns in modes associated with proper orthogonal decomposition from laser-based imaging of the single transverse jet. Corresponding studies involving linear stability theory applied to transverse jet shear layer dynamics are expected to be pursued via an international collaboration with researchers at the Universidade Federal Fluminense (UFF) in Brazil. The proposed studies have the potential to yield unprecedented understanding and identification of control methodologies for future innovations in propulsion and energy generation systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.