Thesis
Shock interaction patterns in carbon dioxide nonequilibrium flows over double-wedges
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2024
- Thesis identifier
- T17184
- Person Identifier (Local)
- 201868855
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Shock interactions in nonequilibrium hypersonic CO2-N2 flows over double-wedge geometries are investigated in detail. Flow patterns resulting from shock interactions typically lead to shock impingement phenomena, which is characterized by localised high heating and pressure loads acting on the surface. Accurately predicting the flow physics involved in shock wave interference and associated surface loads is key to ensure the robust aerodynamic design of high-speed vehicles. While extensive research on shock interactions in air flows can be found in the literature, investigation of carbon-dioxide flows is scarce. This thesis aims to address the need for a thorough understanding of nonequilibrium shock interaction physics in the Martian atmosphere, driven by the growing interest of the aerospace community in exploring the planet. Hypersonic vehicles operate in unique flow environments that are dominated by chemical and thermodynamic phenomena not observed at lower Mach numbers. Accurate simulation of these environments requires complex physical and numerical models to capture physical processes occurring the atomic scale that have a significant impact on surface flow properties. In this work, shock interaction patterns in nonequilibrium CO2-N2 flows are investigated by means of computational fluid dynamics. A coupled framework for simulating nonequilibrium hypersonic flows with any gas mixture is implemented by linking the SU2-NEMO software, a hypersonic CFD code, to the Mutation++ library, that provides thermodynamic, transport, chemistry, and energy transfer models, data, and algorithms allowing for the closure of the Navier-Stokes flow equations implemented in the CFD code. Park’s two-temperature model is considered to model vibrational relaxation and finite-rate chemistry. Patterns of shock interaction are characterised on the basis of Edney’s pioneer classification. Results show that vibrational relaxation plays an active role in the mechanisms of shock interference for carbon-dioxide dominated flows, since the assumptions of simplified models (perfect ideal and thermally perfect gas models) resulted in significant differences in terms of qualitative flow patterns as well as distributions of surface aerothermal loads. It is shown that the effect of decreasing the freestream Mach number on the pattern of shock interaction and surface properties follows the same trend resulting from increasing the angle of the second wedge and from simulating the flow with a gas model where less energy is absorbed by vibrational excitation, and contrary to the trend resulting from increasing the freestream temperature: flow separation regions and shock angles become larger, leading to more complex and stronger mechanisms of interaction. Results indicate there is a threshold of the Mach number and aft wedge angle below which, and above which, respectively, the flow becomes unsteady due to a strong coupling between the separated flow region and the entire shock system. Accounting for vibrational relaxation effects shows to stabilize the entire shock system, by delaying the threshold for which the mechanism of interaction would become unsteady if vibrational excitation were to be neglected. Conversely, the opposite trend is seen for when thermal equilibrium is assumed.
- Advisor / supervisor
- Fossati, Marco
- Resource Type
- DOI
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PDF of T17184 | 2025-02-28 | Public | Download |