Research
Research
We will research several beyond the state-of-the-art methodologies for the adoption of LH2 in turbofan engines, evaluating their performance under operative conditions of civil aviation to achieve an acceptable life of the system. We will research the innovative inclusion of hydrogen into jet engine components. Within the spectrum of technologies considered, there are several permutations of possible systems and approaches Our work will enable us to rank such approaches and inform their introduction by our colleagues in future LH2-powered vehicles. This over-arching aim will set the context of our work and keep the partners focussed on delivering real system benefits.
Combustion Dynamics
Hydrogen has exceptionally low density, high flame speed, high diffusivity (compared to kerosene) and has exhibited increased propensity to thermoacoustic instability. Over the past 70 years, aero-engines combustors have been optimised to use liquid-based fuels which are both incompressible and supplied isothermally. LH2 is compressible with properties that depend strongly on temperature. Transients in fuel system (e.g. in the heat exchanger) are predicted to lead to significant changes in temperature which will impact combustion system performance. Within this phenomenology we will use state of the art facilities (NCCAT) and custom developed numerical tools to delineate the architecture of LH2-based combustors of future engines.
Photo courtesy of University of Loughborough.
Hydrogen Uptake and Thermal Stresses Understanding
Existing rocket engines – such as the Ariane series – are fuelled by LH2 but operate at essentially one power setting and have very limited life. To be commercially viable, civil aircraft engines must operate for thousands of hours (typically 20,000) before being overhauled. Hydrogen can accelerate microstructural damages typical of turbofan engines, and the interactions with the alloys commonly used for engine’s part are still unexplored and uncharacterised. We will then tackle a new highly complex problem that cannot be assessed via current practices, and we will develop a modelling framework capable of capturing the complex stress-temperature-hydrogen uptake interactions with metal alloys.
Image courtesy of Mechanics of Materials Lab, University of Oxford
Fundamental Flow and Heat Transfer Physics
A key challenge is to predict re-laminarization zones that result from large density changes near the critical point. The influence of tube entry effects, surface roughness, curvature and turbulators on steady and transient heat transfer characteristics will be studied and appropriate models developed to aid heat exchanger design and support numerical modelling validation. Our approach will study both normal and para hydrogen. and incorporate the influence of the highly coupled velocity and thermal fields that occur under super-critical flow conditions.
Numerical Modelling of Fluid and Structure
The LH2 fuel system combines high pressure, low mass-flow and low viscosity to present unique turbomachinery challenges. The design of cryogenic hydrogen pumps for civil aviation offers unique challenges. Most modern applications use centrifugal pumps, but pumping of hydrogen with centrifugal machines is difficult because of its low density and low temperatures, which can lead to undesired phenomena like cavitation and thermal stresses. We will address fundamental and applied research issues on the modelling of fuel systems, as well as lay the foundations of a technical community of methods experts knowledgeable on LH2 fuel system science. The aim is the development of numerical codes to model fluid flow and wall stress for hydrogen subject to phase changes and supercritical conditions typical of those encountered in H2-fuelled turbofans.
Science to industry translation and advocacy
Heat exchangers installed into engines will in general be subject to non-uniform, unsteady boundary conditions from the heat providing flow. Significant interaction effects can affect the heat transfer, frosting and thermal stress; such system integration issues represent a key hurdle when translating the fundamental studies to industry. We will develop a methodology for predicting the fuel system temperatures and combustor output during transients for the whole system. The approach will account for system temperature changes as the operating point of the engine changes- specifically as the hydrogen flow rate is modulated for different engine powers. The challenge of validating specific, key sections of the subsystem will also be addressed using National facilities at NCCAT and an NWTF wind tunnel.