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Virtual Seminar: Fall 2020

Speaker: Prof. Christoph Brehm (University of Kentucky)
Title: "Simulations of Particulate-Induced Transition in High-Speed Boundary-Layer Flows"
Hosted By:
Tamer Zaki (MechE)

Date: Friday, October 16, 2020
Time: 3:00 p.m.
Location: Virtual Zoom Online Presentation

Abstract

Various types of particulates with different origins are present in the stratosphere and the role they play in the free-flight boundary layer transition process is not well understood. Atmospheric particulates impinging on the surface of high-speed vehicles trigger disturbances inside the boundary layer which evolve into wavepackets and through exponential growth can provide a path to turbulence. This talk will present particulate-induced transition simulation results for flow conditions relevant to high-speed flight through the atmosphere.
In the first part of the presentation, a newly developed wavepacket tracking strategy coupled with a particle model will be presented. The wavepacket tracking approach, namely AMR-WPT (adaptive mesh refinement wavepacket tracking), relies on (1) the nonlinear disturbance flow formulation of the compressible Navier-Stokes equations, (2) a dual mesh overset approach, and (3) adaptive mesh refinement. The accuracy and efficiency of the AMR-WPT approach has been demonstrated for a wide range of transition mechanisms, e.g., receptivity, first and second mode, and cross-flow instabilities for 2-D and 3-D baseflows. To model particulate-induced transition, AMR-WPT was initially coupled with a particle solver based on the particle-in-cell approach. The second part of this talk will present a higher-fidelity simulation approach where the particle flow is fully-resolved utilizing an immersed boundary method in conjunction with the AMR-WPT method. Both methods are compared for first and second-mode dominated hypersonic transition prediction test cases. A detailed analysis of the simulation results provide insight into the relevant physical mechanisms involved in particle-induced transition. Finally, bi-orthogonal decomposition based on the continuous and discrete eigenmodes of the compressible boundary layer flow is employed to study the receptivity process.

Bio

Dr. Brehm joined the Mechanical Engineering Department of the University of Kentucky (UK) as an Assistant Professor in 2016. Previously, he has worked as 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 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. Dr. Brehm has authored over 60 archival peer-reviewed journal and conference publications. His research is supported by NSF, NASA, ONR, AFOSR, HVSI, and industry partners in close collaboration with several US and international research institutions, such as the University of Oxford, TU Delft, NASA ARC/LaRC/JSC, JPL, HVSI, etc. Dr. Brehm is currently supervising 8 PhD students and 2 post-docs. 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 2021 as well as the co-chair of the 2020 International Conference on Computational Fluid Dynamics (ICCFD).



Upcoming Seminar

Speaker: Prof. Christoph Brehm (University of Kentucky)
Title: "Simulations of Particulate-Induced Transition in High-Speed Boundary-Layer Flows"

Date: Friday, October 16, 2020
Time: 3:00 p.m.
Location: Zoom Virtual Meeting

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