Numerical modelling of hypersonic shock tunnels in thermochemical non-equilibrium

Thesis

Shock tube experiments allow interrogation of non-equilibrium thermochemistry relevant to hypersonic flow conditions. Previous works have shown that due to shot-to-shot variability, a priori numerical methods are unsuitable for modelling these experiments. Prior to this work, the predominant a posteriori numerical method assumed equivalence between a blunt body stagnation line and the core flow in a shock tube. Therefore, the primary aim of this thesis is to develop computationally efficient, reacting gas numerical methods capable of modelling the physical behaviour present in shock tubes.

This work develops analytical approaches to transform results from existing reacting gas numerical methods, to more physical results for appropriate comparison to shock tube data. The transformation provides a simple improvement for legacy methods to implement, and has been applied to rate optimisation activities for the Dragonfly mission to Titan.

A specialised quasi-one-dimensional numerical method is developed to determine the core flow in a shock tube. This is the first a posteriori viscous shock tube method, allowing the effect of the shock layer to be evaluated. The work shows both significant changes to the non-equilibrium region and the charged species number densities away from the shock. A boundary layer model removes mass from the core flow, improving agreement with the physical behaviour present in a shock tube.

The final method derives and implements the first two-dimensional method for conducting a posteriori, viscous, steady, reacting gas analysis of shock tube flows, removing the requirement for boundary layer correlations. This is facilitated by an additional constraint equation, fixing the shock in a desired location via a variable ambient pressure boundary condition.

Two-dimensional effects such as shock curvature and boundary layer properties, including the effect of surface catalycity on the boundary layer, are found to influence shock tube measurements. This results in up to 50% change in expected radiance emissions in wavelength regions dependent on radial property variation.

Authors: Clarke, J

• DOI: 10.5287/ora-xoom0wx8z
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: high temperature gas dynamics; absorption spectroscopy; planetary entry; computational fluid dynamics; emission spectroscopy; aerospace engineering; thermochemistry; hypersonics; shock tube
• Subjects: Aerospace engineering