Kinetic Investigation of High-Speed Flows: Non-Equilibrium, Thermochemistry, and Stability Considerations
Date: March 6, 2026 (Friday)
Time: 13:30
Venue: EA-101
ABSTRACT
This talk presents a comprehensive kinetic analysis of high-speed flows at high altitudes and emphasizes the critical role of high-fidelity numerical methods in capturing non-equilibrium phenomena and flow instabilities. The presentation consists of two main parts: non-equilibrium thermochemistry and stability investigations, in order to demonstrate the scope within which kinetic methods can be used as effective tools.
The first part focuses on the investigation of nitric oxide (NO) ultraviolet (UV) emissions in hypersonic flows. These emissions serve as a rigorous validation tool for high-fidelity thermochemical models used in laser measurements in ground-test facilities and flight tests of hypersonic vehicles. Collisional-radiative models have been constructed using quasi-steady-state (QSS) and overlay mass transport (MassTR) approaches applied to Direct Simulation Monte Carlo (DSMC) flow fields in order to predict the electronic quantum state populations that are critical for determining the UV radiation properties of N2 and NO. The results show that the coupled treatment of electronic quantum state formation and flow transport, a feature often simplified in lower-fidelity models, leads to significantly higher populations and therefore stronger radiation in expansion and wake regions. In addition, the study reveals the sensitivity of NO emission profiles to oxygen dissociation models and vibrational preference mechanisms, emphasizing the necessity of detailed kinetic descriptions for the accurate prediction of radiation signatures. The accurate prediction of these radiation signatures is critical for the design of thermal protection systems on spacecraft re-entering the atmosphere and for reducing communication blackout.
The second part examines flow irregularities and stability in high-speed compression-ramp flows, a common geometry in supersonic and hypersonic vehicles. These flows involve complex interactions among shocks, shear layers, and large separation regions, and they can trigger transition to turbulence, affecting heat transfer and structural integrity. The particle-kinetic DSMC method is used together with data-driven methods such as Spectral Proper Orthogonal Decomposition (SPOD) and continuum-based BiGlobal linear stability analysis. DSMC is particularly effective because it can resolve the internal structure of shock layers in detail and capture non-equilibrium effects that continuum approaches may miss. This approach reveals key instability mechanisms such as reattachment shock oscillations and Kelvin–Helmholtz instabilities. Notably, a previously unknown traveling global mode at the leading edge has been discovered, which can only be resolved through kinetic simulations that capture internal shock structures. The talk will also discuss the nonlinear evolution of these instabilities and present the formation of lambda vortices, which are distinctive indicators of the transition process, as a finding observed for the first time in a kinetic simulation. Understanding these instability mechanisms is critical for predicting when the flow will transition to turbulence, which can lead to significant increases in surface heating and aerodynamic drag on hypersonic vehicles.
ABOUT THE SPEAKER
Irmak Taylan Karpuzcu is pursuing doctoral studies in the Department of Aerospace Engineering under the supervision of Prof. Deborah Levin. He received his master’s degree in 2019 and his bachelor’s degree in 2015 from the Department of Mechanical Engineering, and conducted his graduate research under the supervision of Prof. Cüneyt Sert. He is a certified graduate teaching instructor and holds the title of MAVIS Future Faculty Fellow.
His research focuses on the numerical simulation of high-speed flows and makes use of high-performance computing techniques. His master’s work focused on turbulence modeling in supersonic flows using large eddy simulation. In the first stage of his doctoral studies, he worked on the non-equilibrium thermochemistry of hypersonic flows. He is currently investigating the stability of high-speed laminar flows at high altitudes using kinetic theory, linear stability analysis, and data-driven methods.
CONTACT
Ela Baycan, Department of Mechanical Engineering, Bilkent University
Email: ela@bilkent.edu.tr