Prediction of laminar-turbulent transition is a critical part of the design of hypersonic vehicles because of the large increase in skin-friction drag and surface heating associated with the onset of transition. Conventional high-speed facilities cannot reliably duplicate in-flight transition behavior due to high levels of acoustic noise that dominates the facility disturbances. To enable better use of transition data from conventional facilities and more accurate extrapolation of wind-tunnel results to flight, it is essential to develop an in-depth knowledge of the broadband disturbance environment in those facilities as well as the interaction between the freestream disturbances with laminar boundary layers. Direct numerical simulations (DNS) are now offering new insights into this problem.
In this talk, I will first present our DNS effort to simulate the full-scale axisymmetric nozzle of the Sandia Hypersonic Wind Tunnel at Mach 8 (HWT-8) to obtain a suitable representation of the radiated noise from the tunnel wall. The talk will then discuss our effort of passing the wind tunnel DNS noise field over a sharp 7-degree cone to mimic the disturbance evolution over a cone model in a virtual wind tunnel. All the stages of the transition to turbulence in the cone boundary layer caused by freestream noise are studied, including the generation of second-mode waves through receptivity mechanisms, their linear and nonlinear growth to saturation, their laminar breakdown, and the wall-bounded fully turbulent flow. Finally, I will introduce the ongoing effort of simulating a Mach 8 flow over a blunt cone in the axisymmetric nozzle of the Sandia HWT-8 facility to study the nonmodal growth of traveling disturbances within the entropy layer and to assess the nonmodal optimal growth theory.
Dr. Lian Duan is an associate professor and holder of Honda endowed chair in transportation in the Department of Mechanical and Aerospace Engineering at The Ohio State University (OSU). Before he joined OSU in September 2019, he was an assistant professor at Missouri University of Science and Technology from 2013 to 2019 and worked as a research scientist at the National Institute of Aerospace from 2010 to 2013. He received his Ph.D. in Mechanical and Aerospace Engineering from Princeton University in 2011.
Duan has held research grants with NSF, AFOSR, ONR, NASA, Sandia National Laboratory, and Honda R&D Americas on topics including (but not limited to) compressible turbulence, flow instability and transition, turbulence modeling and control, high-performance and data-driven computing, and automotive aerodynamics.
The significance of his research has been recognized with several accolades including the 2017 Henry J. E. Reid Award, 2014 AFOSR Young Investigator Award, 2015 AIAA St. Louis Section Young Professional Engineer Award, and multiple mentions in the annual highlights of Fluid Dynamics research in Aerospace America.