09-24-2018 | Antonio Di Giovanni: DNS of Roughness-Induced Transition in the Boundary Layer of a Hypersonic Spherical Forebody

106th NIA CFD Seminar: DNS of Roughness-Induced Transition in the Boundary Layer of a Hypersonic Spherical Forebody

Date: Monday, September 24, 2018

Time: 11am-noon (EDT)

Room: NIA, Rm 137

Speaker: Antonio Di Giovanni

Abstract: The laminar-turbulent transition of the boundary layer on spherical forebodies at hypersonic speeds is a fundamental and yet not fully understood problem. Laminar-turbulent transition significantly impacts on skin friction and heat-transfer rates at the wall and, thus, its understanding is related to reliability and costs of re-entry vehicles.

Numerous experimental investigations have been conducted on capsule models with roughness in the last decades. However, further numerical investigations based on new computational methods are still needed. Compared to stability analysis (e.g. linear stability theory and parabolized stability equations), Direct Numerical Simulations allow for a more complete insight into non-linear instability mechanisms. Furthermore, as wind-tunnel experiments at realistic re-entry conditions matching all relevant dimensionless parameters, including the Damköhler number, are extremely difficult to realize, numerical simulations represent an important and often non-substitutable investigation tool.

In this talk, I will present the instability mechanisms in the boundary layer of a capsule-like geometry in the presence of a patch of (pseudo-)random distributed roughness. A set of different simulations are conducted for freestream conditions matching both wind-tunnel (Ma=6) and realistic re-entry (Ma=20) scenarios. In the case of re-entry conditions, the gradual inclusion of chemical and thermal non-equilibrium in the gas modeling will show the influence of the high temperature on the stability properties of the reacting boundary layer in the roughness wake.

Speaker Bio: Antonio Di Giovanni is a PhD student at the Technical University of Munich, Germany. His research includes stability investigations on high-enthalpy hypersonic boundary layers. Current research projects comprehend studies of roughness-induced transition on capsule geometries and Görtler instabilities under consideration of non-equilibrium effects.