Fundamental interaction mechanisms for separation control using tunable flexible materials

University Of Akron, Akron OH

Investigators

Abstract

The flow of air over aircraft wings or turbine blades under certain conditions may not follow a path along the solid surface, but, instead, may ‘separate’ from the surface, resulting in a recirculation region. This ‘flow separation’ can cause an undesirable loss of lift and lead to large fluctuations in pressure and flow speeds. Small triangular protrusions called vortex generators are commonly used to mitigate flow separation by creating regions of swirling flow to re-energize the flow near the wall. Flexible materials, especially those with tunable properties, provide new opportunities to enhance flow control. Potential applications encompass energy, transportation, and national security systems, including improving the safety and performance of aircraft and unmanned aerial vehicle operations in gusty conditions. This project will use experiments and computer simulations to advance understanding of the mechanisms underlying tunable vortex generators. The project will also enhance outreach programs through new laboratory activities, increase undergraduate participation in research, and develop a new graduate course on advanced flow control. Developing tunable flexible vortex generators for a range of critical applications requires the understanding and prediction of (a) fluid-structure interactions between the disturbances naturally present in the flow and the vibration of the flexible vortex generators; (b) generation of unsteady streamwise vortices resulting from this interaction; and (c) the effect of the resulting unsteady vortices on the dynamics of the separating flow. This project will address these requirements using high-fidelity simulations and closely matched water tunnel and wind tunnel experiments. Specific tasks include: (i) performing large eddy simulations and analysis of backward-facing steps with specified inflow forcing; (ii) utilizing scaling analysis to design and study the effect of flexible vortex generators using water tunnel experiments matched fluid-structure-interaction simulations; and (iii) developing reduced order models and evaluating suitable designs for airfoil stall mitigation in a wind-tunnel. This work will advance the fundamental understanding of vorticity dynamics and interplay between the multiple instability mechanisms in a separated shear flow. In addition to aircraft stall mitigation, the detailed study of flexible vortex generators could benefit heat transfer and energy harvesting in other technological applications. 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.