CAREER: Nonlinear stability, input-output analysis, and control of time-varying wall-bounded shear flows

Many engineering systems involve fluid flows that change over time, such as the flow around accelerating transport vehicles, flow control to reduce drag, and flows that remove heat in electronic devices. Time-dependent flows affect drag, heat transfer, and system reliability; however, the analysis of these situations is often limited to steady flow or flow that varies slowly in time. This project will develop new analysis tools that can accurately characterize and predict time-varying flow behavior beyond these limitations. The methods will be applied to flow scenarios with complex time dependence relevant to transport vehicles and thermal management systems. The outcomes will help enable safer aircraft operations during takeoff and landing, improve the fuel efficiency of transport vehicles, and enhance the cooling efficiency of electronic devices and data centers. Research outcomes will be integrated into multi-level education and outreach activities designed to inspire students at all levels to pursue STEM careers. This project will support the advanced manufacturing of transport vehicles. The objective of this project is to develop a suite of nonlinear analysis frameworks for time-varying wall-bounded shear flows, including nonlinear stability analysis, input-output analysis, and feedback control. These new nonlinear analysis tools are tailored to time-varying shear flows for which existing methods based on linearization or steady base flow assumptions fail to capture essential transient and nonlinear effects. The tools will enable rigorous characterization of nonlinear stability and input-output properties in time-varying shear flows based on Lyapunov theory, which will be applied in channel flows with increasing complexity of time dependence, ranging from periodic to non-periodic, and ultimately to unknown time dependence. The nonlinear frameworks will be employed to study (1) drag reduction by wall oscillations, (2) transition to turbulence in accelerating and decelerating channels relevant to aircraft takeoff and landing, and (3) liquid cooling control of electronics by designing the time-dependence of inflow velocity to enhance cooling efficiency. The research will be tightly coupled to a Fluid Learning, Outreach, and Transition education program to inspire students' interest in STEM careers through conducting outreach to a Boat Camp for 5-6th grade students, advising the undergraduate Electric Boat Club in its participation in the Promoting Electric Propulsion boat racing, mentoring high school researchers, and developing graduate course modules. 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. NSF Award ID: 2542711 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Chang Liu | Institution: University of Connecticut, STORRS, CT | Award Amount: $529,999 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2542711 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2542711.html