Alec Linot: Stability analysis of unsteady fluid flows

Title: Stability analysis of unsteady fluid flows

 

Abstract: When studying fluid flow problems, we often wish to know if the flow will remain laminar or transition to turbulence. Understanding this transition is useful for finding the regimes where analytical or easily computable laminar solutions can be used over expensive high-resolution turbulence simulations.  Furthermore, knowing the mechanisms by which a flow transitions to turbulence can inform methods to avoid or promote turbulent transition. While much is known about the stability of stationary flows (e.g., laminar pipe flow), far less is known about the stability of laminar flows that are time-varying and aperiodic. In this seminar, I present our recent work on using nonmodal stability analysis to investigate the stability of flows undergoing acceleration and deceleration. First, I show how perturbations to flows undergoing deceleration can grow orders of magnitude larger than perturbations to stationary or acceleration flows. Then, I present an optimization approach to find the deceleration profile that best avoids this growth. Finally, I end by investigating the stability of a gust impacting an airfoil — a flow undergoing both acceleration and deceleration.