Excellence in Research: Co-axial Flow Mixing and Control using Ultra-High Frequency Actuators

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Innovative fuel-air mixing technologies are essential to the continual advancement of faster and more reliable aircrafts for both national defense and air transportation. This project will focus on a novel fuel injection scheme to enhance and control mixing of a fluid (fuel) with a fast moving air. The proposed scheme consists of two co-axial nozzles: a central nozzle surrounded by an annular one, through which air and fluid are injected simultaneously. While the fluid is supplied through the annular nozzle in a steady stream, the central nozzle injects air in a pulsed manner to enhance mixing. The innovative concept for the proposed injection system is in its ability to pulse the central air jet at very high frequencies (20,000-30,000 pulses per second). It is anticipated that the fluid (fuel) and the high frequency pulsed air will be mixed more effectively in this manner. To investigate this, an experimental fluid mechanics research lab will be equipped with new capabilities utilizing the state-of-the-art, advanced laser-based flow diagnostics that are required for this study. The project will also use educational plans that have been developed based upon established learning theories to provide more effective research experience to underrepresented students in engineering.Major goals of this project include design, development, and characterization through fundamental studies of an active co-flow injection system for enhanced fuel-air mixing at high speeds. The proposed system consists of a supersonic actuation air jet at the inner core that provides large mean and fluctuating velocity profiles in the shear layer of a steadily-injected annular fluid, where the fluctuations occur at a designated and controllable ultra-high frequency. It is expected that the mixing of air with the co-flowing fluid can be improved and controlled using resulting stream-wise vortices that are tailored to the mean flow in this manner. The specific tasks include quantitative characterization of mixing through measurement of seed particle density distribution using planar laser-induced florescence (PLIF) and velocity and vorticity field measurement using particle image velocimetry (PIV). Using these data, the diffusive mixing characteristics of the system (e.g., the timescales of evolution, interfacial area generation and mixing efficiency) will be studied and correlated to the relevant non-dimensional parameters involved. Specific educational activities include targeted infusion of advanced topics useful in research to an undergraduate level fluid mechanics course which provides additional support, and access to students whose pre-college situations may otherwise preclude success in engineering research.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.