The accurate prediction of the laminar-to-turbulent transition process is one of the most challenging problems in fluid dynamics. Even after many decades of research in this area it still is not clear what causes transition in free flight. While there has been a lot of progress on understanding the dominant instability mechanisms the disturbance sources responsible for triggering these instability mechanisms are not well characterized. Various candidates have been discussed in the literature, but no clear evidence points towards one dominant disturbance source. This presentation explores the relevance of atmospheric particles on hypersonic transition in free flight. The presentation gives an overview of all relevant aspects that need to be considered to determine whether atmospheric particles can cause transition to turbulence in free flight. The talk starts by considering the particle properties, concentration of particles in the atmosphere, the receptivity mechanisms and, finally, the modeling fidelity required to predict particle-induced transition. The entire discussion is purely based on theoretical and computational results as there have been no experiments performed so far. To ensure the accuracy of the analysis the final discussion is centered around the modeling fidelity of the numerical simulation approaches used to study the particle-induced transition process.
About the speaker:
Dr. Brehm is an Associate Professor in the Aerospace Engineering Department of the University of Maryland. Previously, he was employed at the University of Kentucky (2012-2016) and before that he was a senior research scientist for the Science Technology Corporation at the Advanced Supercomputing Division at NASA Ames Research Center from 2012 to 2016. He was one of the main developers of the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework and has employed LAVA to study a wide range of unsteady fluid dynamics problems, such as rocket launch site, contra-rotating open rotor, jet impingement, etc. His current research is at the intersection of fundamental numerical methods development and large-scale multi-physics applications. His most recent research efforts have focused on simulating and analyzing transitional and turbulent flows in low and high-speed regimes for fundamental studies in laminar-turbulent transition, turbulence, relaminarization, acoustics, and fluid-structure interaction. He is a member of the NATO Task Force on hypersonic turbulence, several AIAA working groups, and is the co-organizer of the LES AIAA Workshop 2022, the co-chair of the 2022 International Conference on Computational Fluid Dynamics (ICCFD) and the co-organizer of a symposium on high-speed boundary layer transition at the 9th U.S. National Congress on Theoretical and Applied Mechanics 2022.