Fundamental Non-Equilibrium Experiments for Hypersonic Flight

This project falls within the EPSRC Engineering - Fluid Dynamics and Aerodynamics research area.

Context

The project focuses on studying the chemical reaction rates of processes occurring in the shock layer and expansion regions of a vehicle during a low-speed Earth return mission. Speeds between 5-9 km/s will be considered. As atmospheric gases pass through the shockwave at the front of the vehicle, the large kinetic energy is converted into internal energy, resulting in a significant temperature increase. This leads to excitation of different internal degrees of freedom of the shock layer gas and a variety of chemical reactions, each with different associated time scales. Radiation is emitted as a result of high energy molecules dropping to lower energy states and emitting photons at a characteristic frequency. Conditions can be replicated transiently at ground level and the radiation detected, to then determine the chemical species present and the rates of the chemical processes occurring.

Around the aft of an entry vehicle, the inverse process occurs in the form of expansion waves. In both cases, due to the high speed of the vehicle and the relatively small shock and expansion regions, the residence time of a given molecule in each region is very small and thus leaves little time for the chemical processes to reach equilibrium. Without being sure of the extent of the chemical reactions, the surface heat flux experienced by the vehicle, aerodynamic characteristics in the surrounding air and the intensity of different wavelengths of radiation emitted can not be predicted accurately. Uncertainty in the amount of heat release brings uncertainty in the amount of heat shielding required for a vehicle to survive earth re-entry. Improved understanding of non-equilibrium phenomena allows a reduction in heat shielding and thus mass, allowing more equipment to be carried on space exploration missions.

Aims & Objectives

1.Provide data for equilibrium and non-equilibrium regions for a range of radiation wavelengths to investigate the rates of thermochemical processes for low-speed Earth return missions.
2.Apply unsteady expansion technology to capture radiation pre- and post-expansion in a ground test facility and use an analogy to compare to different parts of the expansion waves around the aft of a vehicle.
3.Compare radiation data to well tested compressing flow conditions to enable a cross-comparison of performance between facilities.

Novelty of research methodology

The low-speed compression non-equilibrium data and unsteady expansion analogy will be the first of their kind and therefore make a significant contribution to current literature. Testing has already begun in a new aluminium shock tube, gathering data for UV and near infrared wavelengths. The large 225mm diameter tube produces a high signal to noise ratio for flows where the pressure is low and non-equilibrium is most prominent.

Personnel and Collaboration

The greater project will be a collaborative project involving Prof Matthew McGilvray (Principal Investigator), Dr Tobias Hermann (Optical Diagnostics, lead Postdoc) Prof Benjamin Williams (Laser Diagnostics) and Prof Luca Di Mare (Numerical methods) from the Oxford Hypersonics Group. International collaboration will be undertaken with Prof Ronald Hanson (Stanford University) which will increase capability on absorption spectroscopy. Dr Aaron Brandis and Dr Brett Cruden (NASA Ames) will add further diagnostic and experimental capability by providing equipment for additional infrared and vacuum ultraviolet emission spectroscopy. Prof Richard Morgan (University of Queensland) will undertake equivalent macro-scale experiments. Dr Rowan Gollan (University of Queensland) will bring expertise on the non-equilibrium absorption and emission modelling.