Abstract
In this talk, two topics related to turbulence intensity in compressible boundary layer and incompressible channel flow are presented. For the former topic, the turbulence amplification mechanism within a strong shock-wave/turbulent boundary layer interaction (SBLI) is investigated using direct numerical simulation (DNS) over a 24o compression ramp with a Mach 2.9 inflow. Two distinct turbulence kinetic energy (TKE) hotspots are identified. In contrast to previous studies, this study sheds light on shocklets, characterized by mid-frequency features, as a key factor contributing to the second TKE amplification, which occurs near the reattachment point. Streamline coordinate analysis reveals that the shear effects dominate the TKE production over the flow deceleration effect in the SBLI. The shear effect induced by the rolling up of the boundary layer initiates the first TKE amplification near the wall region at the separation point, followed by flow deceleration due to the main shock wave contributing to the TKE generation. The initial detachment of the shear layer enhances the shear contribution. While TKE decreases above the separation bubble due to the positive mean velocity gradient, TKE amplifies again due to the flow deceleration caused by the secondary shock wave. In addition, the intermittently spawning shocklets above the large-scale structures at boundary layer edge enhance the shear effect on the TKE production. Moreover, the generated TKE subsequently transfers to the local pressure minimum line, thereby establishing a spatially converged maximum TKE line. The second part of the talk discusses the near-wall vortical structures with extreme TKE dissipation rate events within a channel configuration across various Reynolds numbers. Statistical evidence confirms the presence of quasi-streamwise (QS) vortices near regions with extreme TKE dissipation rates, consistent with earlier experimental studies. The temporal behavior of QS vortices during extreme TKE dissipation events is investigated using the Connected Component Labeling and a temporal tracking algorithm based on the velocity of labeled regions. The lifecycle of QS vortices, including the stages of coupled counter-rotating streamwise vortices, tilting, and dissipation, are analyzed. A roll-up phenomenon is observed at the tail of QS vortices when the TKE dissipation rate peaks during the temporal evolution.
About the Speaker
Sang Lee is an assosciate professor at the Korea Advanced Institute of Science and Technology in the Aerospace Engineering department. He earned his bachelors degree in mechanical engineering at Yonsei University and his master’s degree at Stanford University in mechanical engineering in 2002. After completing his military service in the Korean Army in 2004, he then continued on with his doctorate program at the University of Illinois at Urbana-Champaign, earning his PhD in aerospace engineering in 2009. He was a Research Engineer III at the National Renewable Energy Laboratory (Golden, Colorado) until 2016, and moved to the University of New Mexico in the mechanical engineering department as an assistant professor until 2019.
Hosts: Professor Leonardo Chamorro and Professor Tonghun Lee