AME Seminar: David Borgmann

Abstract: Boundary layer separation occurs in many low Reynolds number flows, such as Unmanned Aerial Vehicles (UAVs), leading edges of thin airfoils and turbomachinery blades. Instabilities in the shear layer between the free-stream and separated region cause transition, increase mixing, and result in turbulent reattachment. The displacement effect associated with the region of recirculating fluid and the turbulent boundary layer downstream can drastically reduce aerodynamic performance and efficiency in practical applications and the resulting highly unsteady flow field may increase noise emissions. This seminar will focus on experimental studies of pressure-induced laminar separation bubbles (LSBs) in incompressible flow. Examination of the baseline case is in excellent agreement with direct numerical simulations and stability analysis performed in the UArizona CFD Laboratory. Active Flow Control using ac-DBD plasma actuators is used to amplify the dominant, primary shear layer instability to delay the transition process in the LSB. Results show significant amplification of the primary instability, developing into two-dimensional, coherent vortices in the LSB shear layer suggesting a delay of transition within the LSB. However, a secondary instability resulting from the new time-periodic flow eventually causes a breakdown to turbulence, which is accelerated by the presence of free-stream turbulence

Bio: David Borgmann is a Ph.D. candidate in aerospace engineering at the University of Arizona (UArizona), working in the Turbulence and Flow Control Laboratory under professor Jesse Little. He received his B.S. and M.S. degrees from the Technical University of Berlin in 2014 and 2017, respectively. During his M.S. Thesis, he spent a year in the AME Department at UArizona as a visiting scholar studying active control of turbulent boundary layer separation using fluidic oscillators. His current research is focused on experimental studies of laminar to turbulent transition in separation bubbles, including active flow control.