Turbulent superstructures

Abstract

At moderate to high Reynolds numbers, the separation between the smallest and largest spatial/temporal scales in turbulent boundary layers (TBLs) can be several orders of magnitude. Streamwise elongated regions of high- and low-momentum in the log law layer that can extend up to several boundary layer thicknesses, often referred to as turbulent superstructures, effectively make this scale separation even larger. These superstructures strongly meander in the spanwise direction and carry a relatively large portion of the layer’s turbulent kinetic energy, especially at large Reynolds numbers. Furthermore, an interaction between superstructures and the near-wall dynamics has been observed. Therefore, measurements capable of resolving the small and large scales are important for understanding the overall scaling and dynamics of TBLs. Due to the large range of scales, especially when considering superstructures, these kinds of measurements are challenging. Often, measurement approaches using multiple type of instrumentation or embedded systems are required. In this talk, novel measurement approaches using particle image velocimetry and tracking (PIV/PTV) aimed at resolving and characterizing the largest scales, i.e. superstructures, and the smallest scales near the wall will be discussed.

About the speaker

Dr. Matthew Bross joined Penn State ARL as an assistant research professor in 2022. Prior his current position, he worked as a research scientist and group leader for turbulence research at the Institute of Aerodynamics and Fluid Mechanics at the Universität der Bundeswehr München (UniBw) from 2015 to 2022. He graduated with a Ph.D. in Mechanical Engineering from Lehigh University in 2015. His dissertation, titled “Flow Structure on Unsteady Maneuvering Wings,” was prepared under the supervision of Dr. Donald Rockwell. In the last 10 years, he has focused his professional expertise on fluid mechanics. More specifically, his research topics have studied unsteady maneuvering bio-inspired wings, the structural topology and scaling of high-Reynolds number turbulent wall-bounded flows, and the development and improvement state-of-the-art 2D and 3D digital particle image and tracking velocimetry (PIV/PTV) techniques. Due to his focus on experimental fluid mechanics, he has managed, designed, implemented, and evaluated data for dozens of wind/water tunnel experiments. His research has led to more than 40 high-quality journal publications, refereed proceedings and technical memorandums, with a focus on turbulence research and the development of novel PIV and PTV methods applied to high-speed incompressible and compressible flows.